Author name code: kundu ADS astronomy entries on 2022-09-14 author:"Kundu, M.R." ------------------------------------------------------------------------ Title: Microflares and the Statistics of X-ray Flares Authors: Hannah, I. G.; Hudson, H. S.; Battaglia, M.; Christe, S.; Kašparová, J.; Krucker, S.; Kundu, M. R.; Veronig, A. Bibcode: 2011SSRv..159..263H Altcode: 2011SSRv..tmp..262H; 2011SSRv..tmp...87H; 2011arXiv1108.6203H; 2011SSRv..tmp..243H; 2011SSRv..tmp..163H This review surveys the statistics of solar X-ray flares, emphasising the new views that RHESSI has given us of the weaker events (the microflares). The new data reveal that these microflares strongly resemble more energetic events in most respects; they occur solely within active regions and exhibit high-temperature/nonthermal emissions in approximately the same proportion as major events. We discuss the distributions of flare parameters (e.g., peak flux) and how these parameters correlate, for instance via the Neupert effect. We also highlight the systematic biases involved in intercomparing data representing many decades of event magnitude. The intermittency of the flare/microflare occurrence, both in space and in time, argues that these discrete events do not explain general coronal heating, either in active regions or in the quiet Sun. Title: The Relationship Between Solar Radio and Hard X-ray Emission Authors: White, S. M.; Benz, A. O.; Christe, S.; Fárník, F.; Kundu, M. R.; Mann, G.; Ning, Z.; Raulin, J. -P.; Silva-Válio, A. V. R.; Saint-Hilaire, P.; Vilmer, N.; Warmuth, A. Bibcode: 2011SSRv..159..225W Altcode: 2011SSRv..tmp..263W; 2011SSRv..tmp..244W; 2011SSRv..tmp..164W; 2011arXiv1109.6629W; 2011SSRv..tmp...88W This review discusses the complementary relationship between radio and hard X-ray observations of the Sun using primarily results from the era of the Reuven Ramaty High Energy Solar Spectroscopic Imager satellite. A primary focus of joint radio and hard X-ray studies of solar flares uses observations of nonthermal gyrosynchrotron emission at radio wavelengths and bremsstrahlung hard X-rays to study the properties of electrons accelerated in the main flare site, since it is well established that these two emissions show very similar temporal behavior. A quantitative prescription is given for comparing the electron energy distributions derived separately from the two wavelength ranges: this is an important application with the potential for measuring the magnetic field strength in the flaring region, and reveals significant differences between the electrons in different energy ranges. Examples of the use of simultaneous data from the two wavelength ranges to derive physical conditions are then discussed, including the case of microflares, and the comparison of images at radio and hard X-ray wavelengths is presented. There have been puzzling results obtained from observations of solar flares at millimeter and submillimeter wavelengths, and the comparison of these results with corresponding hard X-ray data is presented. Finally, the review discusses the association of hard X-ray releases with radio emission at decimeter and meter wavelengths, which is dominated by plasma emission (at lower frequencies) and electron cyclotron maser emission (at higher frequencies), both coherent emission mechanisms that require small numbers of energetic electrons. These comparisons show broad general associations but detailed correspondence remains more elusive. Title: Sunspots at centimeter wavelengths Authors: Kundu, Mukul R.; Lee, Jeongwoo Bibcode: 2011IAUS..273..265K Altcode: The early solar observations of Covington (1947) established a good relation between 10.7 cm solar flux and the presence of sunspots on solar disk. The first spatially resolved observation with a two-element interferometer at arc min resolution by Kundu (1959) found that the radio source at 3 cm has a core-halo structure; the core is highly polarized and corresponds to the umbra of a sunspot with magnetic fields of several hundred gauss, and the halo corresponds to the diffuse penumbra or plage region. The coronal temperature of the core was interpreted as due to gyroresonance opacity produced by acceleration of electrons gyrating in a magnetic field. Since the opacity is produced at resonant layers where the frequency matches harmonics of the gyrofrequency, the radio observation could be utilized to measure the coronal magnetic field. Since this simple interferometric observation, the next step for solar astronomers was to use arc second resolution offered by large arrays at cm wavelengths such as Westerbrock Synthesis Radio Telescope and the Very Large Array, which were primarily built for cosmic radio research. Currently, the Owens Valley Solar Array operating in the range 1-18 GHz and the Nobeyama Radio Heliograph at 17 and 34 GHz are the only solar dedicated radio telescopes. Using these telescopes at multiple wavelengths it is now possible to explore three dimensional structure of sunspot associated radio sources and therefore of coronal magnetic fields. We shall present these measurements at wavelengths ranging from 1.7 cm to 90 cm and associated theoretical developments. Title: The IAU Early French Radio Astronomy Project Authors: Orchiston, Wayne; Boischot, A.; Delannoy, J.; Kundu, M.; Lequeux, J.; Pick, M.; Steinberg, J. Bibcode: 2011AAS...21714608O Altcode: 2011BAAS...4314608O In 2006 an ambitious project was launched under the auspices of the IAU Working Group on Historic Radio Astronomy to document important developments in French radio astronomy from 1901 through to the 1960s, in a series of papers published, in English, in the Journal of Astronomical History and Heritage. This successful project has now come to an end with the sixth and final paper in the series about to be published (and a new WG project, on the history of early Japanese radio astronomy, has just been launched).

In this paper we discuss Nordmann's abortive attempt to detect solar radio emission in 1901, and the important roles played by staff from the École Normale Supérieure and the Institut d'Astrophysique in Paris during the 1940s through 60s in developing new radio astronomy instrumentation and pursuing a range of solar and non-solar research projects in Paris itself and at field stations established at Marcoussis, Nançay and the Haute Provence Observatory. Title: High-Energy Emission from a Solar Flare in Hard X-rays and Microwaves Authors: Kundu, M. R.; Grechnev, V. V.; White, S. M.; Schmahl, E. J.; Meshalkina, N. S.; Kashapova, L. K. Bibcode: 2009SoPh..260..135K Altcode: 2009arXiv0908.0385K We investigate accelerated electron energy spectra for different sources in a large flare using simultaneous observations obtained with two instruments, the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz, and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) at hard X-rays. This flare is one of the few in which emission up to energies exceeding 200 keV can be imaged in hard X-rays. Furthermore, we can investigate the spectra of individual sources up to this energy. We discuss and compare the HXR and microwave spectra and morphology. Although the event overall appears to correspond to the standard scenario with magnetic reconnection under an eruptive filament, several of its features do not seem to be consistent with popular flare models. In particular we find that (1) microwave emissions might be optically thick at high frequencies despite a low peak frequency in the total flux radio spectrum, presumably due to the inhomogeneity of the emitting source; (2) magnetic fields in high-frequency radio sources might be stronger than sometimes assumed; (3) sources spread over a very large volume can show matching evolution in their hard X-ray spectra that may provide a challenge to acceleration models. Our results emphasize the importance of studies of sunspot-associated flares and total flux measurements of radio bursts in the millimeter range. Title: Highlighting the history of French radio astronomy. 4: Early solar research at the École Normale Supérieure, Narcoussis and Nançay Authors: Orchiston, Wayne; Steinberg, Jean-Louis; Kundu, Mukul; Arsac, Jacques; Blum, Émile-Jacques; Boischot, André Bibcode: 2009JAHH...12..175O Altcode: The first tentative steps in solar radio astronomy took place during the 1940s and early 1950s as physicists and engineers in a number of countries used recycled World War II equipment to investigate the flux levels and polarisation of solar bursts and emission from the quiet Sun, and sought to understand the connection between this emission and optical features in the solar photosphere and chromosphere. There was also an abiding interest in the terrestrial effects of this solar radio emission. Among these solar pioneers were French radio astronomers from the École Normale Supérieure in Paris. In this paper we review the early solar observations made by them from Paris, Marcoussis and Nançay prior to the construction of a number of innovative multi-element solar interferometers at the Nançay field station in the mid-1950s. Title: Mitigation of geogenic arsenic bearing groundwaters: Assessing the importance of risk substitution arising from waterborne pathogens Authors: Mondal, Debapriya; Polya, David A.; Giri, A. K.; Banerjee, M.; Hegan, A.; Rodriguez-Lado, L.; Bradford, W.; Banerjee, N.; Kundu, M.; Ganguli, B. Bibcode: 2009GeCAS..73Q.893M Altcode: No abstract at ADS Title: High-Energy Emission from a Solar Flare in Hard X-Rays and Microwaves Authors: Kundu, Mukul R.; Grechnev, V. V.; White, S. M.; Schmahl, E. J.; Meshalkina, N. S.; Kashapova, L. K. Bibcode: 2009SPD....40.1920K Altcode: We investigate accelerated electron energy spectra for different sources in a large flare using simultaneous observations obtained with two instruments, the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz, and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) at hard X-rays. This flare is one of the few in which emission up to energies exceeding 200 keV can be imaged in hard X-rays. Furthermore, we can investigate the spectra of individual sources up to this energy. We discuss and compare the HXR and microwave spectra and morphology. Although the event overall appears to correspond to the standard scenario with magnetic reconnection under an eruptive filament, several of its features do not seem to be consistent with popular flare models. In particular we find that (1) microwave emissions might be optically thick at high frequencies despite a low peak frequency in the total flux radio spectrum, presumably due to the inhomogeneity of the emitting source; (2) magnetic fields in high-frequency radio sources might be stronger than sometimes assumed; (3) sources spread over a very large volume can show matching evolution in their hard X-ray spectra that may provide a challenge to acceleration models. Our results emphasize the importance of studies of sunspot-associated flares and total flux measurements of radio bursts in the millimeter range. Title: Advances in Solar Radio Astronomy Authors: Kundu, Mukul R. Bibcode: 2007AAS...210.3801K Altcode: 2007BAAS...39..152K The development of research in Solar Radio Astronomy over the years will be presented. Starting with the early years of solar radio research when discoveries were frequently made,we discuss the evolution of solar radio research into an integral component of solar physics research. We continue with a discussion of contributions made by radio instruments to those made by space solar missions and show that the combined observations are complementary as well as fundamental in nature, especially when it applies to high energy solar phenomena. Title: The Morphology of Decimetric Emission from Solar Flares: GMRT Observations Authors: Kundu, M. R.; White, S. M.; Garaimov, V. I.; Subramanian, P.; Ananthakrishnan, S.; Janardhan, P. Bibcode: 2006SoPh..236..369K Altcode: 2006SoPh..tmp....7K Observations of a solar flare at 617 MHz with the Giant Meter-wave Radio Telescope (GMRT) are used to study the morphology of flare radio emission at decimetric wavelengths. There has been very little imaging in the 500 - 1000 MHz frequency range, but it is of great interest, since it corresponds to densities at which energy is believed to be released in solar flares. This event has a very distinctive morphology at 617 MHz: the radio emission is clearly resolved by the 30″ beam into arc-shaped sources seeming to lie at the tops of long loops, anchored at one end in the active region in which the flare occurs, with the other end lying some 200 000 km away in a region of quiet solar atmosphere. Microwave images show fairly conventional behaviour for the flare in the active region: it consists of two compact sources overlying regions of opposite magnetic polarity in the photosphere. The decimetric emission is confined to the period leading up to the impulsive phase of the flare, and does not extend over a wide frequency range. This fact suggests a flare mechanism in which the magnetic field at considerable height in the corona is destabilized a few minutes prior to the main energy release lower in the corona. The radio morphology also suggests that the radiating electrons are trapped near the tops of magnetic loops, and therefore may have pitch angles near 90˚. Title: Microwave and Hard X-ray Imaging Observations of Energetic Electrons in Solar Flares: Event of 2003 June 17 Authors: Kundu, Mukul R.; Schmahl, E. J.; White, S. M. Bibcode: 2006SPD....37.1306K Altcode: 2006BAAS...38..241K We discuss one large flare using simultaneous observations obtained with two instruments--Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz, and Reuven Ramaty High Energy Solar Spectroscopic imager (RHESSI) in the context of flare models. As we know energetic electrons accelerated to nonthermal energies are seen via microwave and hard X-ray emission from the solar corona. Imaging observations are necessary to study the energetic electrons in flare events. Nonthermal microwave emission during large solar flares is produced by gyrosynchrotron mechanism which involves coronal magnetic fields of at least a few hundred gauss and electrons of energy of a few hundred keV. Hard X-ray emission, on the other hand, is produced by bremsstrahlung from beamed or trapped electrons of a few to hundreds of keV energy. The two different methods of mapping energetic flare electrons therefore complement each other, and provide good means of testing flare models which have been abundant in the recent literature. The RHESSI HXR and NoRH microwave imaging observations of the flare of 2003 June 17 are used here as an example. The flare in question was of class M6.8, and it was observed in AR 10386, a beta-gamma-delta region, two days after its east-limb passage. Title: Radio and Hard X-Ray Imaging Observations of the M5.7 Flare of 2002 March 14 Authors: Schmahl, E. J.; Kundu, M. R.; Garaimov, V. I. Bibcode: 2006ApJ...643.1271S Altcode: We describe a flare of GOES class M5.7 that was observed simultaneously by RHESSI (Ramaty High Energy Solar Spectroscopic Imager) and NoRH (Nobeyama Radio Heliograph). The flare occurred in AR 9866 located near the disk center. The hard X-ray (HXR), microwave, EIT, and TRACE 195 Å observations indicate that the flaring region consisted of a complex of multiple loops. In the microwave domain the source morphology, the timing, the polarization characteristics, and the photospheric magnetic fields clearly indicate that it is of a class characterized as a ``double loop'' configuration, meaning two systems of magnetic flux, each consisting of many smaller loops. The observations suggest the existence of a small loop system created by the emergence of new flux, which interacts with an old flux system, and of a remote flare site that is observed primarily in radio. The former is the main flare site where we observe microwave, HXR, and EUV emissions. In HXR there are two main identifiable loop systems. The first is an elongated one filled with energetic electrons primarily emitting lower energy (12-25 keV) HXR with a colocated microwave source; this source has distinct footpoints at higher X-ray energies. The second loop system is implied by compact HXR sources in opposite magnetic polarities separated by a distance greater than the length of the first loop system. Spectroscopic analysis of the RHESSI data shows that the spectrum can be fitted with a thick-target model with a thermal component and a broken power-law component of the electron energy distribution. This model is used to address the thermal/nonthermal and radio/HXR electron number problems. Title: Nobeyama radio heliograph observations of RHESSI microflares Authors: Kundu, M. R.; Schmahl, E. J.; Grigis, P. C.; Garaimov, V. I.; Shibasaki, K. Bibcode: 2006A&A...451..691K Altcode: Aims.We present a summary of the analysis of thirty microflares, observed simultaneously by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in hard X-rays and by Nobeyama RadioHeliograph (NoRH) in microwaves (17 GHz).
Methods: .We used microflares observed by RHESSI in the energy range 3-25 keV, and for larger events, up to 35 keV. The observations were made 2002, May 2-6.
Results: .We describe the imaging characteristics of these microflares including their locations in hard X-rays and microwaves and the relative positions of the micro-flaring sources. We discuss the brightness temperatures, emission measures and their hard X-ray spectral properties. We see small (mini) flaring loops clearly in NoRH and RHESSI images. The microwave emission often seems to come from the RHESSI foot points (for higher energies), and from the entire small (mini) flaring loop (for lower energies). Sometimes the two (microwave and hard X-ray) sources coincide, at other times they are at opposite ends of a mini flaring loop. Typically, the hard X-ray spectrum of the microwave associated RHESSI microflares can be fit by an isothermal component at low energies (below 10 or 12 keV) and a nonthermal component at higher energies (above 12 keV).
Conclusions: .Microflares in hard X-rays and in microwaves behave like normal flares in many respects. They can have both thermal and nonthermal components appearing in bremsstrahlung and gyrosynchrotron radiation. Title: Flare-Associated Decimeter TypeIV Bursts at High Frequencies Authors: Kundu, M. R.; White, S. M.; Hori, K.; Schmahl, E. J. Bibcode: 2006AGUSMSH24A..06K Altcode: Type IV radio bursts are broadband continuum events associated with solar flares that typically occur after the impulsive phase, can last for tens of minutes and are usually confined to low frequencies, below 200 MHz. However some flares show clear evidence for strong Type IV-like emission that is confined to high frequencies, around 1 GHz. Type IV events require nonthermal electrons and imply the presence of either long-lived energetic electrons trapped in coronal loops, or else ongoing acceleration lasting for tens of minutes following a flare. If, as is widely believed, the emission mechanism of Type IV bursts is plasma emission, then the high- frequency events require electrons at densities of over 3 109 cm-3, far higher densities than are involved in the low frequency Type IV bursts. We present a sample of such high frequency Type IV bursts and analyze their properties and association with other flare phenomena, and discuss their possible sources. Title: A Study of Accelerated Electrons in Solar Flares Using Microwave and X-Ray Observations Authors: Grechnev, Victor V.; Kundu, Mukul R.; Nindos, Alexander Bibcode: 2006PASJ...58...47G Altcode: We consider manifestations of accelerated electrons in microwave and hard X-ray emissions from solar flares. To meet our objectives, we discuss two events -- those of 1999 March 16 and February 16. The first event is a short-duration burst, while the second is a long-duration event. An analysis of the first event leads to the conclusion that: 1) a seemingly single-loop configuration can actually be a double-loop one, and 2) it is possible that the pitch-angle distribution of the radio-emitting electrons can be anisotropic with practically no non-zero pitch angles. The second event shows seemingly intersecting flaring loops, and the formation of a post-eruptive arcade that can proceed as a series of double-loop interactions. From these and other published results, we conclude that: 1) double-loop configurations can be responsible for flares showing diverse morphologies and time profiles; 2) the pitch-angle distribution of accelerated electrons can be strongly anisotropic, with an excess of small angles, contributing to a rather narrow energy range of the microwave-emitting electrons. Title: Microwave and Hard X ray Imaging of Energetic Electrons in Solar Flares: Event of 2003 June 17 Authors: Kundu, M. R.; Schmahl, E. J.; White, S. M. Bibcode: 2006IAUS..233..334K Altcode: We discuss a large flare that was observed simultaneously by RHESSI in hard X-rays and by the Nobeyama Radio Heliograph (NoRH) in microwaves. The imaging observations made both by RHESSI and NoRH show many interesting features which may be relevant for producing realistic flare models. Title: RHESSI & Nobeyama Imaging Observations of the X 2.7 Flare of 2003 Nov 3, 00:58 UT Authors: Kundu, M. R.; Schmahl, E. J.; Garaimov, V. I.; White, S. M. Bibcode: 2005AGUSMSP52A..02K Altcode: We describe the RHESSI HXR and Nobeyama (NoRH) microwave imaging observations of an X-class event that was observed during the great solar activity period of Oct 19--Nov 10, 2003. The flare in question of class X 2.7 was observed in AR 0488 (position N08W66) on 2003 Nov 3, 00:58:33 UT, with a large peak at 01:15:25 UT, and ending at 03:08:19 UT. The maximum fluxes at 17 and 34 GHz are respectively 678 and 536 SFU. Besides the peak at 01:15 there are two other peaks at approx 01:20 and 01:32:30 UT. In NoRP data the peak at 01:20 is the most dominant at frequencies 9.40, 3.75, 2.0 GHz. At 1.0 GHz the emission prior to this peak is fluctuating and a peak with fluctuations exists at around 01:05 UT. The third peak at 01:32:30 UT is spiky and it is nonthermal with a turnover frequency between 17 and 34 GHz. One significant property of the HXR emission (below 12 keV) during the period 01:00 - 01:08 is that the preflare emission, in projection, lies close to and above the W-limb, although the associated microwave source is on the disk. There are two preflare sources (RHESSI at 12-25 keV, and NoRH at 17 and 34 Ghz), but it is not clear how they are related. The RHESSI source seems to coincide in position with the EIT flaring source at its apex. The morphological structure seems to suggest that we are dealing with a loop-top HXR source situated at the top of the EIT flaring loop and flaring sources at 17 and 34 GHz, whose morphology suggests a complex flaring arcade structure. Title: RHESSI and radio imaging observations of microflares Authors: Kundu, M. R.; Trottet, G.; Garaimov, V. I.; Grigis, P. C.; Schmahl, E. J. Bibcode: 2005AdSpR..35.1778K Altcode: We present an analysis of five microflares, three observed simultaneously by RHESSI in hard X-rays and Nobeyama RadioHeliograph (NoRH) in microwaves (17 GHz) and two observed by RHESSI and Nancay RadioHeliograph (NRH) at metric wavelengths (150-450 MHz). Since we have no radio imaging telescopes simultaneously operating at microwave and meter wavelengths in the same time zone, we are obliged to use a different set of metric events in contrast to that used for comparison with the two radio wavelengths. We are interested in using the locations and other imaging characteristics of the events from both RHESSI and radio observations instead of just temporal correlation. So we have used the Nancay (France) metric radioheliograph at 150-450 MHz for this purpose. Here we describe the properties of five events - three in microwaves and two at metric wavelengths. We discuss the brightness temperatures, emission measures and the hard X-ray spectral properties of these microevents. One sees small (mini) flaring loops clearly in NoRH and RHESSI images. The microwave emission often seems to come from the RHESSI foot points (for higher energies), and from the entire small (mini) flaring loop (for lower energies).The RHESSI microflares seem to be associated in position with metric type III bursts. Frequently, the hard X-ray spectrum of the microwave associated RHESSI microflares can be fit by a thermal component at low energies (∼3-12 keV) and a nonthermal component at higher energies (∼12-20 keV). Title: Multi-wavelength study of a coronal mass ejection: a flare event from AR#9393 Authors: Manoharan, P. K.; Kundu, M. R. Bibcode: 2005AdSpR..35...70M Altcode: The active region, AR#9393, produced a number of intense flares during March-April 2001. In this paper, we report the analysis of an X1.1 flare event of April 2, 2001 and its associated coronal mass ejection. The timing and location of the Hα eruption, radio burst activities, and the onset of mass ejection suggest an energy release that occurred close to the surface of the sun. At this region, as shown by the magnetogram, X-ray and EUV images, the field configuration was complex and the 3-D extrapolation revealed the presence of a magnetic null point. Results also suggest that the energy release is followed by the magnetic reconnection between the low-lying loops near the separator point and outlying loops. This study provides the support for the magnetic break-out process to trigger the energy release in eruptive flare event. Title: The configuration of simple short-duration solar microwave bursts Authors: Kundu, M. R.; Nindos, A.; Grechnev, V. V. Bibcode: 2004A&A...420..351K Altcode: Using data from the Nobeyama Radioheliograph (NoRH) we study the source configuration of four simple short-duration 17 and 34 GHz bursts which have also been observed partially by the Yohkoh Soft X-ray Telescope (SXT). Two events are consistent with a single flaring loop configuration. In one of them the flaring loop is resolved in the SXT images. We derive a self-consistent model for this event by comparing the radio observations with gyrosynchrotron model loop calculations. Our best-fit model is able to reproduce both the observed flaring loop shape as well as the fluxes and structures of the radio emission at the peak of the event. The flaring loop is relatively small having a footpoint separation of 16 arcsec and maximum height of 7.7 arcsec. The variation of the magnetic field along the loop is small (800 G at the footpoints and 665 G at loop top) and the loop is filled with electrons with energies up to 10 MeV. The other two bursts show two radio sources; one source being cospatial with a compact bright soft X-ray loop associated with a patch of parasitic magnetic polarity whose photospheric magnetic flux increases before the flares while the other source is not prominent at any other wavelength range. The two sources are connected with diffuse loop-like soft X-ray emission. We infer that these bursts originate from the interaction of two sets of loops with different sizes. Therefore the simple short duration microwave bursts we studied do not always appear in the same configuration. Contrary to previous results not all of them appear as single-loop events. It is possible that some events are caused by two interacting loops. Title: RHESSI and Microwave Imaging Observations of Two Solar Flares Authors: Kundu, M. R.; Schmahl, E. J.; Garaimov, V. I. Bibcode: 2004AAS...204.5402K Altcode: 2004BAAS...36R.757K We present hard X-ray (RHESSI) and microwave (NoRH) imaging observations of two solar flares of M-class observed on March 14 and March 12 of 2002, one located near the disk center and the other near the E-limb. For the March 14 event (near disk center), both hard X-ray and microwave observations indicate that the flaring region consisted of a complex of multiple loops. In microwaves its spatial configuration has a double-loop structure; at the main flare site (primary flaring loop) we observe microwave, HXR, EUV emissions and at a remote site (connected to main site by a long loop) we observe microwaves only due to a strong magnetic field. Some HXR foot point sources (in 25-100 KeV bands) have co-located microwave footpoint sources. The hard X-ray spectrum can be fitted with a thick target model with a thermal component and a broken power-law component. The March 12 E-limb event was fully observed by Nobeyama Radio Heliograph (NoRH), but in hard X-rays it was observed only from around the peak until the end of flare, because of RHESSI night time. In hard X-rays (6-50 KeV) it was clearly a coronal source located above an EIT loop, and it seems to have significant motion in the post flare period. In microwaves it was also a coronal source in both 17 and 34 GHz. Due to the relatively poor resolution of NoRH, the overall source size in radio is large, encompassing the RHESSI source at the start and end of its motion. The spatial maximum of the 17 GHz source appears at a coronal height below the HXR source. The microwave source also shows motion, along with the expansion of the EIT flaring loop. The hard-ray spectral properties of the flare will be discussed. Title: Radio Observations of Rapid Acceleration in a Slow Filament Eruption/Fast Coronal Mass Ejection Event Authors: Kundu, M. R.; White, S. M.; Garaimov, V. I.; Manoharan, P. K.; Subramanian, P.; Ananthakrishnan, S.; Janardhan, P. Bibcode: 2004ApJ...607..530K Altcode: We discuss a filament eruption/coronal mass ejection (CME) event associated with a flare of GOES class M2.8 that occurred on 2001 November 17. This event was observed by the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz. NoRH observed the filament during its eruption both as a dark feature against the solar disk and a bright feature above the solar limb. The high cadence of the radio data allows us to follow the motion of the filament at high time resolution to a height of more than half a solar radius. The filament eruption shows a very gradual onset and then a rapid acceleration phase coincident with the launch of a fast halo CME. Soft X-ray and extreme-ultraviolet (EUV) images show heating in a long loop underneath the filament prior to the flare. The NoRH height-time plot of the filament shows a roughly constant gradual acceleration for 1 hr, followed by a very abrupt acceleration coincident with the impulsive phase of the associated flare, and then a phase of constant velocity or much slower acceleration. This pattern is identical to that recently found to occur in the motion of flare-associated CMEs, which also show a sharp acceleration phase closely tied to the impulsive phase of the flare. When the rapid acceleration occurs in this event, the flare site and the filament are separated by ~0.5 Rsolar, making it unlikely that a disturbance propagates from one location to the other. Models in which a disruption of the large-scale coronal magnetic field simultaneously permits the acceleration of the filament and the flare energy release seem to be a better explanation for this event. Title: Nobeyama Radioheliograph and RHESSI Observations of the X1.5 Flare of 2002 April 21 Authors: Kundu, M. R.; Garaimov, V. I.; White, S. M.; Krucker, S. Bibcode: 2004ApJ...600.1052K Altcode: We present an overview of the radio observations of the X1.5 flare of 2002 April 21 and complementary data from other wavelengths. This flare was fairly well observed by the Ramaty High Energy Spectroscopic Imager (RHESSI) spacecraft and fully observed by the Nobeyama Radioheliograph (NoRH) at 17 and 34 GHz. This long-duration event lasted more than 2 hr and featured a beautiful arcade of rising loops on the limb visible at X-ray, EUV, and radio wavelengths. The main flare was preceded by a small event 90 minutes earlier showing a long EUV loop connecting well-separated radio and hard X-ray sources. The main flare itself starts with a compact radio and hard X-ray source at the eastern end of the region that develops into emission close to the solar surface (and well inside the solar limb) over a large region to the northwest. As the flare proceeds, a large set of loops is seen to rise well above the solar limb. Distinct regions of radio emission with very different time behavior can be identified in the radio images, and, in particular, a peculiar nonthermal source seen in radio and hard X-rays low in the corona at the base of the arcade is seen to turn on 30 minutes after the start of the impulsive phase. At about the same time, an extremely intense burst of coherent radio emission is seen from 500 to 2000 MHz; we speculate that this lower-frequency burst is produced by electrons that are accelerated in the nonthermal source at the base of the arcade and injected into the loop system where they radiate plasma emission in the 1010 cm-3 density plasma at the top of the arcade of loops. This event is striking as a demonstration of the many ways in which a flare can produce radio emission, and the combined data at different wavelengths reveal a diversity of energy release and nonthermal acceleration sites. Title: Long Term Variation of Solar Corona from SOHO/EIT Observations Authors: Zhang, Jie; Kundu, Mukul R. Bibcode: 2004IAUS..223..157Z Altcode: 2005IAUS..223..157Z We present the long term variation of solar corona based on SOHO/EIT observations from 1996 to 2004. EIT provides diagnostics of bulk corona in three channels with overlapping temperature range from 0.5 MK to 2.7 MK and with high spatial resolution. We find that the coronal emission measure increases by a factor of 4 from 2.0times10^{27} cm^{-5} at the solar minimum to 8.0times10^{27} cm^{-5} at the solar maximum. In the meantime, the overall temperature of the corona increases from 1.3 MK to 1.7 MK Title: RHESSI and Microwave Imaging Observations of Two Solar Flares Authors: Kundu, M. R.; Schmahl, E. J.; Garaimov, V. I. Bibcode: 2004IAUS..223..425K Altcode: 2005IAUS..223..425K We describe two flares of GOES class M5.7 and 1.5 which were observed simultaneously by RHESSI (Ramaty High Energy Solar Spectroscopic Imager) and NoRH (Nobeyama Radio Heliograph). Both flares exhibit slow motions suggestive of changing magnetic shear, loop expansion, or gradual reconnection. One flare is clearly a coronal hard X-ray and microwave flare. Title: Microwave and hard x-ray imaging observations of a complex M flare Authors: Schmahl, E.; Kundu, M.; Garaimov, V. Bibcode: 2004cosp...35..872S Altcode: 2004cosp.meet..872S We describe a flare of GOES class M5.7 which was observed simultaneously by RHESSI and NoRH (Nobeyama Radio Heliograph). The flare occurred in active region AR 9866 located near disk center. Both hard X-ray and microwave observations indicate that the flaring region consisted of a complex of multiple loops. In the microwave domain it clearly is of a class characterized by a double loop configuration: a small loop created by the emergence of a new flux interacting with an old flux, which is the main flare site meaning that this is the site where we observe microwave, HXR, EUV emissions, and a remote flare site which is observed only in radio. In HXR there are clearly three loops, two of which have distinct foot points with co-located microwave s source in one foot point; the third loop is large and filled with energetic electrons primarily emitting lower energy (12-25 keV) HXR. The successive energization of the loops gives the illusion of re-orientation with time of RHESSI flaring loops. There is a second peak in flaring emission in both microwaves and HXR, which also shows up as a short duration weak continuum in dynamic spectra (in the frequency range 30-500 MHz, 01:50-01:57 UT). We have carried out spectroscopic analysis of the flare event using RHESSI data. We find that the data can be fitted with a thick- target model with a thermal component and a broken power-law component with a spectral break at an electron energy of 40 keV. The total emission measure rises from the start of the flare to a maximum of ∼ 1.5 × 1049 cm-3. The electron energy distribution below 40 keV is initially harder (δ ∼ 4) than the distribution above the break, but it softens in the middle of the flare, and then hardens in the last few minutes of the flare. The upper slope remains more constant, hardening slightly from δ ∼ 6 at the beginning to 5 near the end. This trend is paralleled by the gradual filling in of a loop between footpoints in the 24-30 keV band, followed by the fading of the loop source between the footpoints. In keeping with this, the 37-55 keV images show a near-constant morphology. Viewed overall, the successive loops inferred from microwaves and HXR appear to show a decrease of magnetic shear as the flare. Title: Radio imaging observations of hard x-ray microflares observed by RHESSI Authors: Kundu, M.; Trottet, G.; Garaimov, V.; Grigis, P. Bibcode: 2004cosp...35..877K Altcode: 2004cosp.meet..877K We describe the properties of two sets of microflares observed simultaneously by RHESSI (Ramaty High Energy Solar Spectroscopic Imager) in hard X-rays and by two radio imaging instruments--NoRH (Nobeyama Radio Heliograph) in microwaves (17 GHz) and NRH (Nancay Radio Heliograph) at metric wavelengths. The two sets of events occurred in two different time zones, and as a result we do not have simultaneous imaging data in microwaves and metric wavlengths for the same RHESSI events. We'll discuss four events--two observed by NoRH in microwaves and two observed by NRH in meter waves, along with RHESSI events. The microwave (17 GHz) events occurred in AR 9934 at 03:58 UT May 3, 2002 and at 05:08 UT May 4, 2002. We have detected microwave (17 & 34 GHz) emissions in association with RHESSI microflares in the energy range 3-50 keV. The microwave emission comes from footpoints for higher energies, and from the entire mini or small flaring loop for lower energies. The relative positions of microwaves and hard X-rays are as they should be in normal flares. Sometimes the two sources coincide, at other times the two sources are at opposite ends of the flaring loop. One sees the mini flaring loops clearly in NoRH images. RHESSI maps at the time of maximum X-ray emission during the event of May 3, 2002 clearly show an X-ray loop in the range 3-6 keV and two footpoints of the loop in the 6-12 and 12-25 keV ranges. These footpoints are located above opposite magnetic polarities as seen in overlays of hard X-ray images on the MDI images. The MDI magnetograms taken before the microflares show rapid evolution of the magnetic field, including sometimes the emergence of a new region. The hard X-ray spectrum of microwave associated RHESSI microflares can be fit by a thermal component (EM ∼ 3× 1046 cm-3) at low energies (3-6 keV) and a nonthermal component (with slope -3.2) at higher energies. The two metric events imaged by NRH occurred on August 5 and September 3, 2003, one located on the disk and the other at the limb. The RHESSI microflare sources are compact. They are accompanied by a series of metric type III bursts at 150-410 MHz originating from sources located above the RHESSI HXR source. Their source positions show frequency dispersion as expected from plasma radiation sources. The properties of these microflare sources in hard X-rays, microwave and meter wavelengths will be discussed. Title: Radio Observations of Rapid Acceleration in a Slow Filament Eruption/Fast CME Event Authors: Kundu, M. R.; White, S. M.; Garaimov, V. I.; Manoharan, P. K.; Subramanian, P.; Ananthakrishnan, S.; Janardhan, P. Bibcode: 2003AGUFMSH21A..06K Altcode: We discuss a filament eruption/coronal mass ejection (CME) associated flare event of GOES class M2.8 that occurred on November 17, 2001. This event was observed simultaneously by Nobeyama RadioHeliograph (NoRH) at 17 and 34 GHz and by the Giant Meterwave Radio Telescope (GMRT) in India at 1060 MHz. The flare occurred in active region 9704 at S18E41. NoRH observes the filament during its eruption both as a dark feature against the solar disk and a bright feature above the solar limb. The filament eruption shows a very gradual onset and then a rapid acceleration phase coincident with the launch of a fast halo CME. The flare on the disk in microwaves has a gradual rise, a broad maximum and a gradual decay. At 1060 MHz, its time profile had three impulsive peaks. The NoRH height--time plot of the filament shows a roughly constant gradual acceleration for an hour, followed by a very abrupt acceleration coincident with the impulsive phase of the associated flare. Soft X-ray images show heating in a long loop underneath the filament prior to the flare. The impulsive behavior of 1060 MHz emission combined with high brightness temperatures indicated the existence of nonthermal electrons in loops that clearly are not the same as the loops containing the microwave-emitting electrons. The latter are dominated by thermal bremsstrahlung and agree well with the EUV and soft X-ray loops. This study is consistent with recent findings that the rapid acceleration of flare--associated CMEs is closely tied to the impulsive phase of the flare. A trigger is required to cause the rapid acceleration to occur at the same time as the flare even though the two events are spatially well separated. We speculate that this trigger is provided by some kind of reconnection in the multiple flux systems that exist between the flaring active region and the erupting filament. Title: Giant Meterwave Radio Telescope observations of an M2.8 flare: Insights into the initiation of a flare-coronal mass ejection event Authors: Subramanian, Prasad; Ananthakrishnan, S.; Janardhan, P.; Kundu, M. R.; White, S. M.; Garaimov, V. I. Bibcode: 2003SoPh..218..247S Altcode: 2003astro.ph..9661S We present the first observations of a solar flare with the GMRT. An M2.8 flare observed at 1060 MHz with the GMRT on 17 November 2001 was associated with a prominence eruption observed at 17 GHz by the Nobeyama radioheliograph and the initiation of a fast partial halo CME observed with the LASCO C2 coronagraph. Towards the start of the eruption, we find evidence for reconnection above the prominence. Subsequently, we find evidence for rapid growth of a vertical current sheet below the erupting arcade, which is accompanied by the flare and prominence eruption. Title: Radio and Hard X-Ray Images of High-Energy Electrons in an X-Class Solar Flare Authors: White, S. M.; Krucker, S.; Shibasaki, K.; Yokoyama, T.; Shimojo, M.; Kundu, M. R. Bibcode: 2003ApJ...595L.111W Altcode: We present the first comparison between radio images of high-energy electrons accelerated by a solar flare and images of hard X-rays produced by the same electrons at photon energies above 100 keV. The images indicate that the high-energy X-rays originate at the footpoints of the loops dominating the radio emission. The radio and hard X-ray light curves match each other well and are quantitatively consistent with an origin in a single population of nonthermal electrons with a power-law index of around 4.5-5. The high-frequency radio spectral index suggests a flatter energy spectrum, but this is ruled out by the X-ray spectrum up to 8 MeV. The preflare radio images show a large hot long-lived loop not visible at other wavelengths. Flare radio brightness temperatures exceed 109 K, and the peak in the radio spectrum is as high as 35 GHz: both these two features and the hard X-ray data require very high densities of nonthermal electrons, possibly as high as 1010 cm-3 above 20 keV at the peak of the flare. Title: Coronal Structure of a Flaring Region and Associated Coronal Mass Ejection Authors: Manoharan, P. K.; Kundu, M. R. Bibcode: 2003ApJ...592..597M Altcode: We report the multiwavelength investigations of an eruptive flare event that occurred on 2001 April 2 at about 11 UT. The manifestations associated with this flare event have been studied from the near-Sun region to about 0.5 AU. The Hα images from the Meudon Spectroheliograph reveal a fast spectacular eruption of plasmoids from the flare site to the west and a Moreton wave disturbance propagating toward the south. A bright, fast, wide coronal mass ejection (CME) associated with this eruptive event was imaged by SOHO/LASCO and the remote-sensing interplanetary scintillation technique. The radio measurements from the Nançay Radioheliograph and Tremsdorf Radio Telescope have been useful in identifying the radio signatures of the CME's initiation. The metric type II radio bursts produced at the time of CME onset also propagate toward the west, and their positions coincide with the magnetic null point, which was located at the southwest part of NOAA active region 9393. The timings and positions of the radio bursts, the Hα eruption, and the CME onset as well as the magnetic field configuration suggest a release of energy at the null point, and as indicated by the Moreton wave, the eruption starts close to the chromospheric or low coronal level. The results support the ``breakout'' scenario proposed by S. Antiochos and coworkers, and they are also suggestive that the energy release is followed by magnetic reconnection between the low-lying loops near the separatrix and the loop system above them. Title: RHESSI and Microwave Imaging Observations of Two Microflares Authors: Garaimov, V. I.; Kundu, M. R.; Grigis, P. C. Bibcode: 2003SPD....34.1603G Altcode: 2003BAAS...35..833G We describe two microflares which occurred in the AR 9934 at 03:58 UT May 3, 2002 and at 05:08 UT May 4, 2002. AR 9934 was a complex region which contained a sunspot with a strong negative polarity of the magnetic field on the north side and a bipolar region on the south side. Analysis of the MDI images shows fast evolution of the south part of the region. TRACE images show many small loops in the south part of AR and the complex loop which connected the north sunspot to the south side of the region. We have observations of both of these events by Nobeyama Radio Heliograph and RHESSI. The NoRH 17 GHz maps show loop like structure of the radio source which has a maximum above the sunspot land it connects to the south side of AR. RHESSI maps superimposed on the NoRH maps show that X-ray emission in the range 3-25 keV are located inside the radio contours. During both events hard X-ray emission was located in the south part of the AR. RHESSI maps corresponding to the maximum X-ray emission during the event of May 3, 2002 clearly show an X-ray loop in the range 3-6 keV and two footpoints of the loop in the 6-12 and 12-25 keV ranges. These footpoints are located above opposite magnetic polarities as seen in overlays of hard X-ray images on the MDI image. Also hard X-ray emission seems to be brighter from the northern footpoint than from the other. The hard X-ray images of the event of May 4, 2002 shows a small X-ray loop (smaller than size of the loop in the previous event), located close to the same position relative to the active region. We calculated the hard X-ray spectrum, temperature and emission measure for both events. Title: Quasi-periodic Pulsations in a Solar Microwave Burst Authors: Grechnev, V. V.; White, S. M.; Kundu, M. R. Bibcode: 2003ApJ...588.1163G Altcode: Quasi-periodic pulsations in solar flares can provide important information on physical conditions in flaring regions. In this paper, we study a microwave burst that showed deep quasi-periodic pulsations. The most dramatic feature of this event has been discussed by Asai and coworkers. In the second of four bursts during the flare, strongly modulated pulsations appear in radio images from the eastern end of a long loop and in hard X-rays from the western end of the loop. We show, in addition, that (1) at least five distinct radio sources with very different time profiles can be identified, including emission from the long loop connecting the modulated radio and X-ray sources; (2) substructure is also present in the radio emission from the eastern end of the long loop during the first burst of the flare, but with timescales shorter than in the second burst; (3) radio modulations are seen at the western end of the loop during the second burst but at a level some 20 times weaker than at the eastern end; (4) these radio modulations at the western end of the loop, like the hard X-ray modulations at the same location, appear to lead the modulations at the eastern end by about 0.5 s, but all have the same period. The period of the modulation can be explained by MHD oscillations of the loop ~120" long connecting the sources: both oscillations that change the magnetic field strength in the loop, such as propagating fast-mode waves, and torsional oscillations that change the direction of the magnetic field in the loop can explain the observed properties of the modulation of the radio emission. An impulsive reconnection episode is a plausible source of oscillating fast-mode waves and is consistent with some other aspects of the event. However, it is difficult to reconcile the strength of the radio modulations at the eastern end of the loop with their delay relative to the emissions at the western end, where the modulation is observed to be much weaker. If the electrons originate at the western end where the main energy release seems to occur, and the modulation is imposed on them there before they propagate 1010 cm to the other end of the loop, any effects due to a spread in electron energies or pitch angles would lead to a spread in propagation times that should smooth out the modulation of the radio emission from the remote source, as should any trapping of electrons in the loop: yet the radio emission from the eastern end of the loop shows much stronger modulation than the radio and hard X-ray emission from the western end of the loop. Title: Nobeyama Radio Heliograph and RHESSI Observations of the X1.5 Flare of April 21, 2002 Authors: Kundu, M. R.; Garaimov, V. I.; White, S. M.; Krucker, S. Bibcode: 2003SPD....34.1812K Altcode: 2003BAAS...35..841K We present radio observations of the X1.5 flare of April 21, 2002, and complementary data from other wavelengths. This flare was fairly well observed by the spacecraft RHESSI and fully observed by the Nobeyama Radio Heliograph at 17 and 34 GHz. This long-duration event lasted more than 2 hours and features a beautful arcade of rising loops on the limb visible at X-ray, EUV and radio wavelengths. The main flare was preceded by a small event 90 minutes earlier showing a long EUV loop connecting well-separated radio and hard X-ray sources. The main flare itself starts with a compact radio and hard X-ray source at the eastern end of the region that is followed by emission close to the solar surface (well inside the solar limb) over a large region to the northwest. As the flare proceeds a large set of loops is seen to rise well above the solar limb. Distinct regions of radio emission with very different time behaviour can be identified in the radio images, and in particular a peculiar nonthermal 17 GHz source low in the corona at the base of the arcade is seen to turn on 30 minutes after the start of the impulsive phase. At about the same time an extremely intense burst of coherent radio emission is seen from 500 to 2000 MHz: we speculate that this lower-frequency burst is located at the top of the arcade of loops. Title: Distinctive spatial configuration of a class of microwave flaring sources Authors: Kundu, M. R.; Garaimov, V. I. Bibcode: 2003AdSpR..32.2497K Altcode: We discuss a class of microwave flares whose source regions exhibit a distinctive spatial configuration; the primaryenergy release in these flares results from the interaction between emerging magnetic flux and an existing overlying region. Such events typically exhibit radio, X-ray and EUV emission at the main flare site (the site of interaction) and in addition radio emission at a remote site up to 1 × 10 5 km away in another active region. We have identified and studied more than a dozen microwave flares in this class, in order to arrive at some general conclusions on reconnection and energy release in such solar flares. Typically, these flares show a gradual rise showing many subsidiary peaks in both radio and hard X-ray light curves with a quasi-oscillatory nature with periods of 5-6 seconds, a bright compact X-ray & EUV emitting loop in the main flare source, a delay of the radio emission from the remote source relative to the main X-ray-emitting source. The magnetic field in the main flare site changes sharply at the time of the flare, and the remote site appears to be magnetically connected to the main flare site. Title: Radio observations of explosive energy releases on the Sun Authors: Kundu, M. R.; White, S. M. Bibcode: 2003dysu.book..288K Altcode: This chapter is devoted to a discussion of the radio observations of explosive energy releases (normal flares and small-scale energy releases) on the Sun. Radio imaging observations of solar flares and coronal transients and the relationship of radio phenomena with those observed in hard and soft X-rays, and underlying physics are discussed. Title: Distinctive spatial configuration of a class of microwave flaring sources Authors: Kundu, M. R.; Garaimov, V. I. Bibcode: 2002ESASP.506..319K Altcode: 2002ESPM...10..319K; 2002svco.conf..319K We discuss a particular spatial configuration of a class of microwave flaring regions in which the primary energy release results from the interaction between emerging magnetic flux and an existing overlying region. Such events typically exhibit radio and X-ray emission at the main flare site (the site of interaction) and in addition radio emission at a remote site up to 1×105 km away in another active region. We have identified and studied more than a dozen microwave flares in this class, in order to arrive at some general conclusions on reconnection and energy release in such solar flares. Title: The Physical Properties of a Flaring Loop Authors: White, S. M.; Kundu, M. R.; Garaimov, V. I.; Yokoyama, T.; Sato, J. Bibcode: 2002ApJ...576..505W Altcode: We use high-resolution radio observations to study the physical parameters of a flaring loop. The loop is visible at radio wavelengths because of gyrosynchrotron emission by nonthermal electrons (energies typically above several hundred keV) accelerated by the flare. We are able to measure the loop thickness and length with a precision on the order of 1". We find that the loop length increases from about 60" initially to about 80" in the decay phase of the event. The loop (averaged along its length) initially is no more than 3" wide. The soft and hard X-ray data obtained with the Soft X-Ray Telescope and Hard X-Ray Telescope on the Yohkoh satellite are consistent with the same loop as observed at radio wavelengths (although the soft X-ray morphology has some small differences early in the event). This event was accompanied by a coronal mass ejection and a coronal dimming visible in Solar and Heliospheric Observatory Extreme-Ultraviolet Imaging Telescope images, so it involved a very large volume of the corona, yet the radio observations clearly indicate that much of the energy release in the low corona was restricted to a region apparently no more than 2000 km across. As the event proceeds, the loop develops a bright feature at the loop top in both the radio and soft X-ray images that cannot be reproduced in gyrosynchrotron loop models in which the electron distribution has relaxed by pitch angle scattering to fill the loop. This prevents us from using the flare properties to measure the magnetic field strength and variation along the loop. The bright loop-top source may require that trapping of electrons take place at the loop top late in the event. Title: Multiple-loop structure of a solar flare from Microwave, EUV and X-ray Imaging Data Authors: Garaimov, V. I.; Kundu, M. R. Bibcode: 2002SoPh..207..355G Altcode: We present the results of an analysis of a flare event of importance M2.8 that occurred at 00:56 UT 28 August 1999. The analysis is based upon observations made with the Nobeyama radioheliograph (NoRH) and polarimeters (NoRP), TRACE, SOHO/MDI, EIT, and Yohkoh/SXT. The images show a very complex flaring region. Pre-flare TRACE and EIT images at 00:24 UT show a small brightening in the region before the flare occurred. The active region in which the flare occurred had evolving magnetic fields, and new magnetic flux seems to have emerged. The X-ray and radio time profiles for this event show a double-peaked structure. The polarimeter data showed that the maximum radio emission (1200 s.f.u.) occurred at 9.4 GHz. At 17 GHz the NoRH images appear to show four different radio sources including the main spot and the main flare loop. Most of the microwave emission seems to originate from the main flare loop. Comparison of BATSE and microwave time profiles at 17 and 34 GHz from the main sunspot source shows that these profiles have similar structures and they coincide with the hard X-ray peaks. The maximum of the flare loop emission was delayed by 10 s relative to the second maximum of the sunspot associated flare emission. Analysis of SXT images during the post-flare phase shows a complex morphology - several intersecting loops and changes in the shape of the main flare loop. Title: Multiwavelength Study of a Coronal Mass Ejection: Eruption from AR#9393 Authors: Manoharan, P. K.; Kundu, M. R. Bibcode: 2002AAS...200.3610M Altcode: 2002BAAS...34..694M We report the investigation of one of the coronal mass ejections unleashed by the largest active region, AR9393, of the current solar cycle. This mass ejection was associated with an X1.1 flare that occurred on April 2, 2001 at about 11 UT and also showed small effect in terms of energetic particle. The analysis of H-alpha images obtained from the Meudon spectroheliograph shows a fast eruption towards the north-west direction and wave-like propagation from the eruption site. The acceleration of the ejecta results in a speed of about 150-200 km/s close to the disk. The associated radio emission observed with the Nancay Radioheliograph in the frequency range 160-327 MHz shows radio emitting regions moving towards north with time and with increasing wavelength. The mass ejection observed with the coronagraphs on board LASCO/ SOHO is consistent with the eruption seen in the H-alpha. We discuss the formation and morphology of the ejection and its interplanetary consequences. Title: Distinctive Spatial Configuration of a Class of Microwave Flaring Sources Authors: Kundu, M.; Garaimov, V. I. Bibcode: 2002AAS...200.6806K Altcode: 2002BAAS...34..756K We discuss a particular spatial configuration of a special class of microwave flaring regions (first identified by Hanaoka) in which the primary energy release results from the interaction between emerging magnetic flux and an existing overlying region. Such events typically exhibit radio and X-ray emission at the main flare site (the site of interaction) and in addition radio emission at a remote site up to 2 x 105 km away in another active region. We have identified and studied more than a dozen microwave flares in this class, in order to arrive at some general conclusions on reconnection and energy release in such solar flares. Typically, these flares show a gradual rise showing many subsidiary peaks in both radio and hard X-ray light curves with a quasi-oscillatory nature with periods of 5-6 seconds, the presence of a bright compact X-ray-emitting loop in the main flare source, a delay of the radio emission from the remote source relative to the main X-ray-emitting source, higher circular polarization in the radio emission of the remote source than in the main source, and stronger photospheric magnetic field in the remote source. We show that the magnetic field in the main flare site changes sharply at the time of the flare, and that the remote site is magnetically connected to the main flare site sometimes only up to the time of the main impulsive phase, at which point the magnetic connection to the remote site may be broken and further flare manifestations are largely confined to the main flare site. This severing of the magnetic connection between two well-separated active regions may be an intrinsic part of the energy release in this flare. Title: Multiple-loop structure of a solar flare from Microwave, EUV and X-ray Imaging Data. Authors: Garaimov, V.; Kundu, M. Bibcode: 2002AAS...200.6805G Altcode: 2002BAAS...34..755G We present the results of the analysis of a flare event of importance M2.8 that occurred at 00:56 UT Aug 28, 1999. The analysis is based upon observations made with the Nobeyama Radio Heliograph(NoRH) and Polarimeters(NoRP), TRACE, SOHO/MDI, EIT and Yohkoh/SXT. The images show a very complex flaring region. Pre-flare TRACE and EIT images at 00:24 UT show a small brightening in the region before the flare occurred. The active region in which the flare occurred had evolving magnetic fields, and new magnetic flux seems to have emerged.The X-ray and radio time profiles for this event show a double peaked structure. The polarimeter data showed that the maximum radio emission (1200 sfu) occurred at 9.4 GHz. At 17 GHz the NoRH images appear to show four different radio sources including the main spot and the main flare loop. Most of the microwave emission seems to originate from the main flare loop. Comparison of BATSE and microwave time profiles at 17 and 34 GHz from the main sunspot source shows that these profiles have similar structures and they coincide with the hard X-ray peaks. The maximum of the flare loop emission was delayed by 10 sec relative to the second maximum of the sunspot associated flare emission. Analysis of SXT images during the post-flare phase shows a complex morphology - several intersecting loops and changes in the shape of the main flare loop. Title: Multiwavelength study of a coronal mass ejection: Eruption from AR#9393 Authors: Manoharan, P.; Kundu, M. Bibcode: 2002cosp...34E1014M Altcode: 2002cosp.meetE1014M We report the investigation of one of the coronal mass ejections unleashed by the largest active region, AR9393, of the current solar cycle. This mass ejection was associated with an X1.1 flare that occurred on April 2, 2001 at about 11 UT and also with energetic particle flux. The analysis of H-alpha images obtained from the Meudon spectroheliograph shows a fast eruption towards the north-west direction and wavelike propagation from the eruption site. The acceleration of the ejecta results in a speed of about 150-200 km/s close to the disk. The associated radio emission observed with the Nancay Radioheliograph in the frequency range 160-327 MHz shows radio emitting regions moving towards north with time and with increasing wavelength. The mass ejection observed with the coronagraphs on board LASCO/ SOHO is consistent with the eruption seen in the H-alpha. We discuss the formation and morphology of the ejection and its interplanetary consequences. Title: Radio observations of high energy solar flares Authors: Kundu, Mukul R. Bibcode: 2002HiA....12..379K Altcode: In this paper we discuss some recent observations of radio emission produced by high energy electrons resulting from solar flares. We discuss the spatial structure of simple weak spiky burst emissions observed simultaneously, at 17 and 34 GHz with the Nobeyama Radio Heliograph (NoRH). Using simultaneous imaging observations obtained by Yohkoh/HXT and SXT along with NoRH 17&34 GHz observations, we attempt to model a relatively stronger and longer flare using gyrosynchrotron mechanism for the flaring radio emission. Title: Multiple-Loop Structure of a Solar Flare from Microwave, EUV and X-Ray Imaging Data Authors: Garaimov, V. I.; Kundu, M. R. Bibcode: 2002mwoc.conf..233G Altcode: We present the results of analysis of a flare event of importance M2.8 that occurred at 00:56 UT Aug 28, 1999. The analysis is based upon observations made with the Nobeyama Radio Heliograph(NoRH) and Polarimeters(NoRP), TRACE, SOHO/MDI,EIT and Yohkoh/SXT. MDI, TRACE, EIT, Soft X-ray and radio images show a very complex structure of the flaring region. Pre-flare TRACE and EIT images at 00:24UT show a small brightening in the region before the flare occurred. The active region in which the flare occurred had changing magnetic fields, and a new magnetic flux seems to have emerged. The X-Ray and radio time profiles for this event show a double peaked structure. The polarimeter data showed that the maximum radio emission (1200sfu) occurred at 9.4 GHz. At 17GHz there appears to be four different radio sources including the main spot and the main flare loop. Most of the microwave emission seems to originate from the main flare loop. Comparison of BATSE and microwave time profiles at 17 and 34GHz from the main sunspot source shows that these profiles have similar structures and they coincide with the Hard X-ray peaks. The maximum of the flare loop emission was delayed by 10 sec relative to the second maximum of the sunspot associated flare emission. Analysis of SXT images during the post-flare phase shows a complex morphology - several intersecting loops and changes in the shape of the main flare loop. Implications of the complex morphology of both radio and X-ray flaring sources will be discussed. Title: Distinctive Spatial Configuration of a Class of Microwave Flaring Sources Authors: Kundu, M.; Garaimov, V. Bibcode: 2002cosp...34E.632K Altcode: 2002cosp.meetE.632K We discuss a particular spatial configuration of a class of microwave flaring regions in which the primary energy release results from the interaction between emerging magnetic flux and an existing overlying region. Such events typically exhibit radio and X-ray emission at the main flare site (the site of interaction) and in addition radio emission at a remote site up to 2 × 105 km away in another active region. We have identified and studied more than a dozen microwave flares in this class, in order to arrive at some general conclusions on reconnection and energy release in such solar flares. Typically, these flares show a gradual rise showing many subsidiary peaks in both radio and hard X-ray light curves with a quasi-oscillatory nature with periods of 5-6 seconds, the presence of a bright compact X-ray-emitting loop in the main flare source, a delay of the radio emission from the remote source relative to the main Xray-emitting source, higher circular polarization in the radio emission of the remote source than in the main source, and stronger photospheric magnetic field in the remote source. We show that the magnetic field in the main flare site changes sharply at the time of the flare, and that the remote site is magnetically connected to the main flare site sometimes only up to the time of the main impulsive phase, at which point the magnetic connection to the remote site may be broken and further flare manifestations are largely confined to the main flare site. This severing of the magnetic connection between two well-separated active regions may be an intrinsic part of the energy release in such flare. Title: Double Loop Configuration of a Flaring Region from Microwave, Extreme-Ultraviolet, and X-Ray Imaging Data Authors: Kundu, M. R.; Grechnev, V. V.; Garaimov, V. I.; White, S. M. Bibcode: 2001ApJ...563..389K Altcode: We use extensive multiwavelength data to study a flare belonging to the interacting-loop class of events identified by Hanaoka. The class of flares is identified morphologically from the presence of two well-separated radio sources in 17 GHz images (in this event, 160" apart), with only one source showing soft X-ray emission. This event shows many of the other properties apparently shared by this class of flares: a gradual rise showing many subsidiary peaks in both radio and hard X-ray light curves with a quasi-oscillatory nature, the presence of a bright compact X-ray-emitting loop in the main flare source, a delay of the radio emission from the remote source relative to the main X-ray-emitting source, higher circular polarization in the radio emission of the remote source than in the main source, and stronger photospheric magnetic field in the remote source. The new results of our analysis are that we are able to show, using a sequence of magnetograms, that the magnetic field in the main flare site changes sharply at the time of the flare, and further we argue that the remote site is magnetically connected to the main flare site only up to the time of the main impulsive phase, at which point we believe the magnetic connection to the remote site was broken and further flare manifestations are largely confined to the main flare site. This severing of the magnetic connection between two well-separated active regions may be an intrinsic part of the energy release in this flare. The region around the main flare site also exhibits rotation in the magnetogram in the period leading up to the flare. Radio and hard X-ray oscillations with periods of order 5-10 s are observed in the rise phase of this event. If they are due to transverse oscillations of the flare loop at the Alfvén speed, then the density in the loop is inferred to be of order 1011 cm-3 and to increase with time as expected. Title: Reconciling Extreme-Ultraviolet and Radio Observations of the Sun's Corona Authors: Zhang, J.; Kundu, M. R.; White, S. M.; Dere, K. P.; Newmark, J. S. Bibcode: 2001ApJ...561..396Z Altcode: The Sun's corona, which is composed of plasma at a temperature of a few millions of degrees, can be best viewed in two electromagnetic domains, one from wavelengths of a few angstroms to hundreds of angstroms (in the soft X-ray and EUV domain), the other from wavelengths of a few centimeters to several tens of centimeters (in the radio domain). In this paper, we present a quantitative comparison of coronal observations made in these two domains with high spatial resolution over the full disk of the Sun. The EUV observations were taken with the EIT (Extreme-Ultraviolet Imaging Telescope) on board SOHO (Solar and Heliospheric Observatory), and the radio observations were taken with the VLA (Very Large Array). The two sets of images show very similar morphologies, indicating that the different wavelengths originate from common solar features. We predict radio fluxes using the temperature and emission measure of the corona calculated from EIT observations, adopting Meyer's table of coronal abundances for the calculations. In each of the seven observations investigated, there always exists a good linear correlation in the pixel-by-pixel correlation plot between the predicted and the observed radio flux for coronal features over a wide range of flux variation. Nevertheless, the predicted radio flux is systematically larger than that observed by a factor of 2.0+/-0.2, on average. We attribute the difference to the underestimation of the abundance of Fe relative to H in the abundances adopted by Meyer. On this basis, we place the absolute Fe abundance in the corona at 7.8×10-5, which has an enrichment factor of 2.4 relative to the accepted photospheric Fe abundance. Title: Possible Radio Evidence of Magnetic Reconnection in Solar Flares Authors: Kundu, Mukul R.; Grechnev, Victor V. Bibcode: 2001APS..DPPLM1002K Altcode: We present possible radio evidence of magnetic reconnection in solar flares.We discuss one specific solar flare -an LDE event of GOES class M3.2 that was observed with the Nobeyama Radio Heliograph (NoRH) in Japan as well as with the Soft X-ray telescope aboard the satellite Yohkoh.The event was also observed in H-alpha and with metric dynamic spectrum analyzers.Our evidence is based upon the facts that we observed a bright microwave source-blob at 17 and 34 GHz near the intersection of two apparently intersecting flaring loops or as a loop-top source above the flaring loop.The bright microwave source is clearly nonthermal and its time profile is similar to that of the flaring foot point microwave sources; and in the late decay phase of the event the microwave source structure is similar to that of the corresponding SXR source. The event was accompanied by a Moreton wave (evidence of shock wave ) and a type II radio burst (a consequence of the shock).We discuss the observations in relation to a specific flare model that involves magnetic reconnection. Title: Metric Radio Emission Associated with X-Ray Plasmoid Ejections Authors: Kundu, M. R.; Nindos, A.; Vilmer, N.; Klein, K. -L.; Shibata, K.; Ohyama, M. Bibcode: 2001ApJ...559..443K Altcode: In this paper we report the first detection of metric/decimetric radio emission associated with two soft X-ray plasmoid ejecta events that occurred during two limb flares observed by the Yohkoh SXT. In the first event a loop started to rise slowly (~10 km s-1) before the beginning of the hard X-ray impulsive phase of the flare. At about the onset of the impulsive flare, there was acceleration of the ejecta, resulting in a speed of 130 km s-1 and finally to ~200 km s-1. The associated radio emission was observed with the Nançay radioheliograph (NRH) in the frequency range of 230-450 MHz. It was an unpolarized continuum that lasted 8-10 minutes. The 410 MHz source was located close to the height where the plasmoid was last identified in the SXT images. In the second event an eruption resulted in the expansion of a large-scale, looplike feature and the development of two plasmoid ejecta which moved in different directions. The speed of the ejecta was 60-100 km s-1. In this event, the associated radio emission was a long-lasting (about 2 hr) continuum observed from 450 to 164 MHz. The onset of the low-frequency emission was delayed with respect to the onset of the high-frequency emission. In both cases the radio sources were located above the soft X-ray ejecta in the general direction of the prolongation of the ejecta movement. In both cases the radio emission comes from nonthermal electrons which are accelerated in close relationship with the propagation of the X-ray plasmoid: as the plasmoid reaches higher altitudes, it interacts with increasingly more extended magnetic field lines and new coronal sites of production of nonthermal electrons are created. Title: On the Temporal Relationship between Coronal Mass Ejections and Flares Authors: Zhang, J.; Dere, K. P.; Howard, R. A.; Kundu, M. R.; White, S. M. Bibcode: 2001ApJ...559..452Z Altcode: The temporal relationship between coronal mass ejections (CMEs) and associated solar flares is of great importance to understanding the origin of CMEs, but it has been difficult to study owing to the nature of CME detection. In this paper, we investigate this issue using the Large Angle and Spectrometric Coronagraph and the EUV Imaging Telescope observations combined with GOES soft X-ray observations. We present four well-observed events whose source regions are close to the limb such that we are able to directly measure the CMEs' initial evolution in the low corona (~1-3 Rsolar) without any extrapolation; this height range was not available in previous space-based coronagraph observations. The velocity-time profiles show that kinematic evolution of three of the four CMEs can be described in a three-phase scenario: the initiation phase, impulsive acceleration phase, and propagation phase. The initiation phase is characterized by a slow ascension with a speed less than 80 km s-1 for a period of tens of minutes. The initiation phase always occurs before the onset of the associated flare. Following the initiation phase, the CMEs display an impulsive acceleration phase that coincides very well with the flares' rise phase lasting for a few to tens of minutes. The acceleration of CMEs ceases near the peak time of the soft X-ray flares. The CMEs then undergo a propagation phase, which is characterized by a constant speed or slowly decreasing in speed. The acceleration rates in the impulsive acceleration phase are in the range of 100-500 m s-2. One CME (on 1997 November 6, associated with an X9.4 flare) does not show an initiation phase. It has an extremely large acceleration rate of 7300 m s-2. The possible causes of CME initiation and acceleration in connection with flares are explored. Title: A Multiwavelength Study of Three Solar Flares Authors: Kundu, M. R.; Nindos, A.; White, S. M.; Grechnev, V. V. Bibcode: 2001ApJ...557..880K Altcode: In this paper we seek a self-consistent model for three strong limb flares observed at 17 and 34 GHz by the Nobeyama radioheliograph and also in soft X-rays and hard X-rays by the Yohkoh SXT (Soft X-Ray Telescope) and HXT (Hard X-Ray Telescope) instruments. Additional radio spectral data were provided by the Nobeyama polarimeter. The flare geometry is simple, with one well-defined flaring loop in each event. The 17 and 34 GHz emissions are optically thin gyrosynchrotron radiation from energetic electrons that outlines the flaring loops and peaks close to the loop tops. We infer that the variation of magnetic field along the loops is very small. We try to reproduce the observed radio morphologies and fluxes using a model gyrosynchrotron loop. The results of our modeling rely on the model magnetic field geometry that we choose. Although the exact loop geometry cannot be constrained from a two-dimensional snapshot, we choose for simplicity a line-dipole magnetic field, and the model field lines are circular. The SXT/HXT images are used to provide the physical parameters of the model loops. The high-frequency polarimeter data give the energy spectral index of the radio-emitting electrons. We could not reconcile the observed radio morphologies and fluxes using classic dipole magnetic field models. The best-fit model that uses the same input parameters for both frequencies and partly reconciles the observed 17 and 34 GHz morphologies and fluxes is produced when we invoke a magnetic field with constant strength along the model loop. These model loops have uniform thickness. The derived densities of the radio-emitting electrons are (1-6)×104 cm-3 with energy limits between 60 and 5000 keV. These models are the best fits we can get under the best assumptions we can justify, but they do not in fact match the radio morphologies very well; their problems and limitations are discussed. Title: Seemingly intersecting flaring loops in microwaves: Possible radio evidence for reconnection Authors: Kundu, M. R.; Grechnev, V. V. Bibcode: 2001EP&S...53..585K Altcode: We present possible radio evidence of magnetic reconnection in a solar flare—an LDE event of GOES class M3.2 that was observed on 1999 February 16 on the disk. Our evidence is based upon the facts that we observed a bright microwave source-blob at 17 and 34 GHz near the intersection of two seemingly intersecting flaring loops or as a loop-top source above one flaring loop. The bright microwave source is clearly non-thermal and its time profile is similar to those of the flaring footpoint microwave sources; and in the late decay phase of the event the microwave source structure is similar to that of the corresponding SXR source. Title: Double Loop Configuration of a Flaring Region from Microwave, EUV and X-ray Imaging Data Authors: Garaimov, V. I.; Kundu, M. R.; Grechnev, V. V.; White, S. M. Bibcode: 2001AGUSM..SP51A04G Altcode: We present the results of a study of a flare of importance M1.7 that was observed with the Nobeyama Radio Heliograph (NoRH), SOHO/EIT and MDI and Yohkoh/HXT & SXT. The flare ocurred in a complex of two active regions AR~8741 and AR~8739, which were separated by ~ 3 arc min. The main flaring region was AR~8741, which consisted of two compact oppositely polarized components as judged by MDI magnetogram data. 17~GHz and 34~GHz microwave emissions as well as EUV, and hard and soft X-ray emissions from the flare originated primarily from the vicinity of the compact components of opposite polarity in AR~8741. There was some 17~GHz flaring emission from AR~8739. Clearly, we are dealing with a large magnetic loop connecting AR~8741 and AR~8739, as well as a compact loop in AR~8741 which was the main flare site. One of the magnetic components of the compact loop increased in field strength approximately 1 hour prior to the flare onset. MDI magnetograms showed some other changes in the magnetic fields associated with the compact loop. We suggest that the interaction of the compact loop with the large loop was responsible for causing the flare. The radio source structures at 17 and 34 GHz along with EUV, hard and soft X-ray source structures of the flaring region will be presented. Title: The Physical Properties of a Flaring Coronal Loop Authors: White, S. M.; Kundu, M. R.; Garaimov, V. I.; Yokoyama, T. Bibcode: 2001AGUSM..SP42A06W Altcode: We present high resolution radio and X-ray images of emission from nonthermal electrons trapped in a flaring coronal loop and measure various physical properties of the loop, including the loop thickness as a function of position along the loop and intensity profiles along the loop. Gyrosynchrotron modelling provides a complementary method for inferring parameters such as the magnetic field variation along the loop, and we compare the results of the two approaches. Both agree that there is little variation in magnetic field strength along the loop; this purely radio measurement thus supports the same inference derived from measurements of EUV and X-ray loop thicknesses. Title: Intersecting Flaring Loops in Microwaves: Possible Radio Evidence for Magnetic Reconnection Authors: Kundu, M. R.; Grechnev, V. V. Bibcode: 2001AGUSM..SP51A05K Altcode: We present possible radio evidence of magnetic reconnection in a solar flare - an LDE event of GOES class M3.2 that was observed on 1999 February 16 on the disk. Our evidence is based upon the facts that we observed a bright microwave source - a bright blob at 17 and 34~GHz near the intersection of two apparently intersecting flaring loops or as a loop-top source above one flaring loop. The bright microwave source is clearly nonthermal and its time profile is similar to those of the flaring footpoint microwave sources, and in the late decay phase of the event the microwave source structure is similar to that of the corresponding SXR source. The loop-top microwave source shows a movement of order 10 km/s, similar to that observed by Yohkoh in soft X-rays in one LDE event which was considered to be a reconnection event. It is important to note that in the late decay phase this event was associated with CGRO/BATSE 100-300 keV energy electrons which appear to originate primarily from the footpoints of one flaring loop. There are data available in Hα from Hida observatory in Japan which show an ejection during this apparent reconnection event. Title: A Radio Study of the Evolution of Spatial Structure of an Active Region and Flare Productivity Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Raulin, J. -P. Bibcode: 2001ApJS..133..467K Altcode: We present the results of a radio study of the evolution of an active region through its flare productivity. The radio study was carried out with data obtained by the Nobeyama Radio Heliograph at 17 GHz. We chose the active region AR 7515, which appeared at the east limb on 1993 May 23 and then evolved during its passage across the disk. We followed its evolution until June 2. This region produced many small flares. We consider this region to be a typical active region in the sense that it did not produce any large flares, but a large number of weak flares. We investigate the optical and magnetic development of the region and show how this affects the locations of the flaring activity. We discuss a number of events in detail in order to investigate the roles of nonthermal and thermal radio emission in the flares. The nonthermal gyrosynchrotron emission generally occurs in regions of strong magnetic fields, is generally circularly polarized, and often varies rapidly in time. On the other hand, gradual radio components tend to be thermal and only weakly polarized, if at all. An interesting aspect of evolution of the flares in this region is that many of the flares in the early phase of the evolution show strong but brief nonthermal radio emission in the impulsive phase followed by gradual thermal emission, whereas in the last 3 days more gradual events without a strong spike of radio emission in the impulsive phase tend to be seen. Correspondingly, the flare images suggest that the radio sources are more compact during the early phases and more extended in the last half of the period covered. The most dominant component of the preflare region is often not the component that undergoes immediate flaring. Sometimes a number of components in the preflare region participate in the flare process together. We speculate that these component sources are unresolved compact bipolar loops that flare in sequence. Loop-loop interactions occurring at many different sites at the same time seems to be a less plausible explanation of these events. Title: Spatial Structure of Simple Spiky Bursts at Microwave/Millimeter Wavelengths Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T.; Grechnev, V. V. Bibcode: 2001ApJ...547.1090K Altcode: We present the results of a study of spatial structure of sources of microwave and millimeter bursts with simple spiky time profiles at 17 and 34 GHz, similar to those found to be common at 3 mm wavelength. These bursts are of short duration, with fast 2-4 s rise time to peak, followed by a rapid exponential decay. When mapped at high spatial resolution with the Nobeyama Radio Heliograph (NoRH), the radio images show direct evidence that the radio sources are compact bipolar loops: source sizes are less than 5" and three of the five events studied show closely spaced oppositely polarized components in the circular polarization maps. All five events are located directly over magnetic neutral lines in the photosphere. The soft X-ray behavior is not entirely consistent with the Neupert effect in these events, since all five events show a rise in the soft X-ray flux well before any nonthermal electrons are present in the corona and the ratio of peak soft X-ray flux to peak radio 17 GHz flux may vary by many orders of magnitude from one event to the next. The abrupt time profiles of these events and their physical properties are consistent with a single-loop scenario in which magnetic energy release and acceleration of nonthermal electrons are confined to a compact localized region. Title: Spatial Distribution and Temporal Evolution of Coronal Bright Points Authors: Zhang, Jie; Kundu, Mukul R.; White, Stephen M. Bibcode: 2001SoPh..198..347Z Altcode: We present a statistical study of the spatial distribution and temporal evolution of coronal bright points (BPs) by analyzing a continuous set of observations of a quiet-Sun region of size 780'' × 780'' over a period of 55 hours. The main data set consists of observations taken by EIT (the Extreme-ultraviolet Imaging Telescope on board the SOHO spacecraft) in its Fe xii 195 Å channel which is sensitive to coronal plasma of temperature ∼ 1.5 MK; we also use soft X-ray observations by SXT (Soft X-ray Telescope on the Yohkoh spacecraft) which is sensitive to coronal plasma of temperature > 2.5 MK. The flux histogram for all pixels in EIT 195 Å images indicates that BPs have a power law flux distribution extending down to a level of 3σ (σ, root mean square deviation) above the average flux of the quiet Sun, while the bulk quiet Sun has a Gaussian-like flux distribution. Using a 3σ intensity threshold, we find a spatial density of one BP per 90 Mm × 90 Mm area, or equivalently 800 BPs for the entire solar surface at any moment. The average size of a BP is 110 Mm2. About 1.4% of the quiet-Sun area is covered by bright points and the radiation from all BPs is only about 5% of that from the whole quiet Sun. Thus, the atmosphere above quiet-Sun regions is not energetically dominated by BPs. During the 55-hour period of EIT observations, we identify 48 full-life-cycle BPs which can be tracked from their initial appearance to final disappearance. The average lifetime of these BPs is 20 hours, which is much longer than the previously reported 8 hours based on Skylab X-ray observations (Golub et al., 1974). We also see shorter life times and smaller numbers of BPs in the soft X-ray images than in the EIT 195 Å observations, suggesting that the temperature of BPs is generally below 2 MK. Title: The Absolute Abundance of Iron in the Solar Corona (CD-ROM Directory: contribs/white) Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.; Kundu, M. R. Bibcode: 2001ASPC..223.1361W Altcode: 2001csss...11.1361W No abstract at ADS Title: Nonthermal Flare Emission from MEV-Energy Electrons at 17, 34, and 86 GHZ Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T. Bibcode: 2000ApJ...545.1084K Altcode: We present analyses of two solar flares observed with high spatial resolution at 86 GHz with the BIMA millimeter-wavelength telescope and at 17 and 34 GHz with the Nobeyama radioheliograph. The flares were observed on 1998 November 24 and 1999 May 1. At millimeter wavelengths these are impulsive events, and therefore they must be produced by MeV-energy electrons. The present study using simultaneous observations of two flares at 86, 34, and 17 GHz provides an excellent opportunity to study high-energy electrons with high spatial resolution observations at three optically thin frequencies. The morphology of millimeter emission can reveal both the properties of the MeV-energy electrons and the nature of the coronal magnetic field lines where they radiate. One of the two events we present is the first clear case of a λ=3 mm source in which both footpoints of a loop are detected. In the second event the polarization image at 17 GHz also suggests a bipolar or looplike morphology. Such morphological observations can be used to constrain the nature of the magnetic field in the solar corona. Title: Solar Flare Physics Authors: Schmahl, Edward J.; Kundu, Mukul R. Bibcode: 2000STIN...0104608S Altcode: During the past year we have been working with the HESSI (High Energy Solar Spectroscopic Imager) team in preparation for launch in early 2001. HESSI has as its primary scientific goal photometric imaging and spectroscopy of solar flares in hard X-rays and gamma-rays with an approx. 2 sec angular resolution, approx. keV energy resolution and approx. 2 s time resolution over the 6 keV to 15 MeV energy range. We have performed tests of the imager using a specially designed experiment which exploits the second-harmonic response of HESSI's sub-collimators to an artificial X-ray source at a distance of 1550 cm from its front grids. Figures show the response to X-rays at energies in the range where HESSI is expected to image solar flares. To prepare the team and the solar user community for imaging flares with HESSI, we have written a description of the major imaging concepts. This paper will be submitted for publication in a referred journal. Title: Radio Detection of a Rapid Disturbance Launched by a Solar Flare Authors: Janardhan, P.; White, S. M.; Kundu, M. R. Bibcode: 2000SPD....31.0243J Altcode: 2000BAAS...32Q1290J This paper reports 333 MHz observations of motion associated with a solar flare at a speed of 26000 km s-1. The motion is seen from a radio source which suddenly starts moving during the flare. At its peak the radio source covers a quiet region of dimension 500 arcsec. The disturbance itself does not seem to radiate, but it excites coronal features which continue to radiate after it passes. The inferred velocity is larger than any previously inferred velocity of a disturbance in the solar atmosphere apart from freely-streaming beams of accelerated electrons. The observed motion of the source at a fixed frequency, low polarization and moderate bandwidth are more consistent with the typical properties of moving Type IV radio bursts than with classical coronal--shock--associated Type II bursts. Title: Soft X-Ray and Gyroresonance Emission above Sunspots Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Shibasaki, K.; Gopalswamy, N. Bibcode: 2000ApJS..130..485N Altcode: Using Yohkoh SXT and Nobeyama 17 GHz data, we have studied the soft X-ray and microwave emission above several stable, large sunspots near central meridian passage. Our study confirms the well-known fact that soft X-ray emission is depressed above sunspots. It also shows that the distribution of their soft X-ray intensity is not uniform; usually the darkest pixels are associated with the umbra or the far edges of the leading part of the penumbra while the following part of the penumbra may contain higher intensity pixels associated with brighter loops. For the first time, we present a systematic survey of the temperatures and emission measures of the soft X-ray material above sunspots. Sunspots always contain the lowest temperatures and emission measures in the active regions. The mean umbral temperature is 1.8×106 K, and the mean penumbral temperature is 2.4×106 K. The mean umbral and penumbral emission measures are logEM=26.60 cm-5 and logEM=27.00 cm-5, respectively. The differences between the umbral and penumbral plasma temperatures are physically significant. The higher penumbral values imply that the loops associated with the penumbrae are generally hotter and denser than the loops associated with the umbrae. The highest sunspot temperatures and emission measures are still lower than the average active region parameters but higher than the quiet-Sun plasma parameters. The coronal radiative energy loss rate above the umbrae is 15% higher than the radiative loss rate of the quiet-Sun plasma but a factor of 8.3 lower than the typical active region radiative loss rate. The radio emission comes from the gyroresonance mechanism, and, as expected, it is sensitive to the magnetic field rather than the soft X-ray-emitting plasma. Title: The Absolute Abundance of Iron in the Solar Corona Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.; Kundu, M. R. Bibcode: 2000ApJ...534L.203W Altcode: 2000astro.ph..4007W We present a measurement of the abundance of Fe relative to H in the solar corona using a technique that differs from previous spectroscopic and solar wind measurements. Our method combines EUV line data from the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory with thermal bremsstrahlung radio data from the VLA. The coronal Fe abundance is derived by equating the thermal bremsstrahlung radio emission calculated from the EUV Fe line data to that observed with the VLA, treating the Fe/H abundance as the sole unknown. We apply this technique to a compact cool active region and find Fe/H=1.56×10-4, or about 4 times its value in the solar photosphere. Uncertainties in the CDS radiometric calibration, the VLA intensity measurements, the atomic parameters, and the assumptions made in the spectral analysis yield net uncertainties of ~20%. This result implies that low first ionization potential elements such as Fe are enhanced in the solar corona relative to photospheric values. Title: Microwave/Millimeter Wavelength Bursts with Simple Spiky Time Profiles Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T. Bibcode: 2000SPD....31.0242K Altcode: 2000BAAS...32..818K We report the detection at 17 and 34 GHz of microwave and millimeter bursts which have simple spiky time profiles similar to those found to be common at λ = 3 mm. These bursts are of short duration, with fast 2 - 4 sec rise time to peak, followed by an exponential decay. These bursts can be of any intensity, from 1 sfu to 10's of sfu; they are very strongly polarized (> 50%), and they have similar properties regardless of the nature of the active region in which the bursts originate. The bursts seem to originate in compact sources which are generally unresolved with 15" and 7" resolution of the Nobeyama Radio Heliograph at 17 and 34 GHz respectively. We provide both direct and indirect evidence that these compact sources are low-lying bipolar loops. The direct evidence follows from the physical appearance of the loop as well as from the bipolar nature of the loop. The indirect evidence follows from the offset in position of the footpoint emission in microwaves and hard X-rays, implying a compact asymmetric loop with microwaves originating from the stronger magnetic field foot point and the hard X-rays originating from the weaker field foot point. Title: The Absolute Abundance of Iron in the Solar Corona Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.; Kundu, M. R. Bibcode: 2000SPD....31.1301W Altcode: 2000BAAS...32Q.845W We present a measurement of the abundance of Fe relative to H in the solar corona using a technique which differs from previous spectroscopic and solar wind measurements. Our method combines EUV line data from the CDS spectrometer on SOHO with thermal bremsstrahlung radio data from the VLA. The coronal Fe abundance is derived by equating the thermal bremsstrahlung radio emission calculated from the EUV Fe line data to that observed with the VLA, treating the Fe/H abundance as the sole unknown. We apply this technique to a compact cool active region and find Fe/H = 1.56 x 10-4, or about 4 times its value in the solar photosphere. Uncertainties in the CDS radiometric calibration, the VLA intensity measurements, the atomic parameters, and the assumptions made in the spectral analysis yield net uncertainties of order 20%. This result implies that low first ionization potential elements such as Fe are enhanced in the solar corona relative to photospheric values. Title: Observations and models of a flaring loop. Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E. Bibcode: 2000BAAS...32..818N Altcode: No abstract at ADS Title: Observations and Models of a Flaring Loop Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E. Bibcode: 2000SPD....31.0243N Altcode: Simultaneous images of a flaring loop at two frequencies are used to model the magnetic structure of the loop and the energy distribution of the radiating electrons. The imaging data were obtained with the VLA at 5 and 15 GHz. Additional spectral data were provided by the OVRO Solar Array at several frequencies between 2 GHz and 15 GHz. At 15 GHz, the flare emission was optically thin and came from the footpoints of the flaring loop, while at 5 GHz the loop itself was outlined. Most of the 5 GHz emission was optically thick and its spatial maximum was close to the loop top. A striking feature of the observations is that the 5 GHz emission does not reach down to the 15 GHz footpoints. We compare the observations with calculations of gyrosynchrotron emission from an inhomogeneous magnetic loop in order to determine the conditions in the flaring loop. The best fit to the OVRO fluxes was reached with a model flaring loop with photospheric footpoint magnetic field strength of 870 G. The thickness of the model loop was small compared to its footpoint separation. The energy spectral index of the energetic electrons was 3.7 and their number density was 7.9 x 107 cm-3. The low and high energy cutoffs of the nonthermal electrons were 8 and 210 keV. The 5 GHz emission in this model is at low harmonics (3--7) and harmonic effects are responsible for the weak 5 GHz emission at the footpoints. The absence of electrons above 210 keV is necessary in this model to explain why no emission is observed from the loop top at 15 GHz. That model reproduced well the high frequency part of the OVRO flux spectrum as well as the VLA spatial structure. Thus comparisons between the spatially--resolved observations and models reveal the three-dimensional structure of the loop geometry. Title: LASCO and EIT observations of CMEs associated with flares Authors: Zhang, J.; Dere, K. P.; Howard, R. A.; Kundu, M. R.; White, S. M. Bibcode: 2000SPD....31.0906Z Altcode: 2000BAAS...32..841Z Coronal mass ejections (CME) and flares are two primary causes of adverse space weather. These two solar eruptive phenomenon are often observed to be associated with each other. Yet the relationship between them is not well known. With unprecedented LASCO (Large-Angle and Spectrometric Coronagraph) and EIT (Extreme-ultraviolet Imaging Telescope) observations combined with simultaneous HXT (Hard X-ray Telescope), GOES and other flare observations, we pursue to make a comprehensive study on the spatial, temporal and energetic relationship between CMEs and flares. In order to make accurate measurement of the onset time of CMEs, we primarily select CME events whose source regions are close to the limb and which are well observed by LASCO/C1 from 1.1 to 3 solar radii. Although a flare occurs in a rather small area of active region, the CME's source region often covers much larger longitudinal and latitudinal extension. Some CMEs occur simultaneously with flare (within only a few minutes), however, some CMEs occur well before the flares (more than 30 minutes earlier). Fast CMEs are associated with strong flares. These studies are aimed to understand the initiation process of solar eruptive phenomenon, and to fit a variety of observational aspects into a consistent picture. Title: Observations and Models of a Flaring Loop Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E. Bibcode: 2000ApJ...533.1053N Altcode: Simultaneous images of a flaring loop at two frequencies are used to model the magnetic structure of the loop and the energy distribution of the radiating electrons. The imaging data were obtained with the VLA at 5 and 15 GHz. Additional spectral data were provided by the Owens Valley Radio Observatory (OVRO) solar array at several frequencies between 2 and 15 GHz. At 15 GHz, the flare emission was optically thin and came from the footpoints of the flaring loop, while at 5 GHz the loop itself was outlined. Most of the 5 GHz emission was optically thick, and its spatial maximum was close to the loop top. A striking feature of the observations is that the 5 GHz emission does not reach down to the 15 GHz footpoints. We compare the observations with calculations of gyrosynchrotron emission from an inhomogeneous magnetic loop in order to determine the conditions in the flaring loop. The best fit to the OVRO fluxes was reached with a model flaring loop with photospheric footpoint magnetic field strength of 870 G. The thickness of the model loop was small compared with its footpoint separation. The energy spectral index of the energetic electrons was 3.7, and their number density was 7.9×107 cm-3. The low- and high-energy cutoffs of the nonthermal electrons were 8 and 210 keV, respectively. The 5 GHz emission in this model is at low harmonics (3-7), and harmonic effects are responsible for the weak 5 GHz emission at the footpoints. The absence of electrons above 210 keV is necessary in this model to explain why no emission is observed from the loop top at 15 GHz. That model reproduced well the high-frequency part of the OVRO flux spectrum as well as the VLA spatial structure. Thus, comparisons between the spatially resolved observations and models reveal the three-dimensional structure of the loop geometry. Title: Radio Detection of a Rapid Disturbance Launched by a Solar Flare Authors: White, S. M.; Janardhan, P.; Kundu, M. R. Bibcode: 2000ApJ...533L.167W Altcode: We report the direct observation of motion associated with a solar flare at a speed of 26,000 km s-1. The motion is seen from a radio source at 0.33 GHz, which suddenly starts moving during the flare. At its peak, the radio source covers a quiet region of dimension 500". Emission from any given location is sporadic. The disturbance itself does not seem to radiate, but it excites coronal features that continue to radiate after it passes. The inferred velocity is larger than any previously inferred velocity of a disturbance in the solar atmosphere apart from freely streaming beams of accelerated electrons. The observed motion of the source at a fixed frequency, low polarization, and moderate bandwidth are more consistent with the typical properties of moving type IV radio bursts than with classical coronal shock-associated type II bursts, but any disturbance at such a high velocity must be highly supersonic and should drive a shock. We speculate that the disturbance is associated with the realignment of magnetic fields connecting different portions of an active region. Title: Solar Flare Physics Authors: Schmahl, Edward J.; Kundu, Mukul R. Bibcode: 2000STIN...0034022S Altcode: In the extended portion of this grant (January 1-March 31, 2000), we have continued our previous efforts (January 1-December 31, 1999) in studies of Fourier imaging methods applied to hard X-ray flares. In particular, we have performed theoretical analysis of the "Forward-Fitting" method in collaboration with Dr. Markus Aschwanden, (Lockheed-Martin Palo Alto Research lab) in support of the HESSI (High Energy Solar Spectroscopic Imager) mission to enable rapid imaging of solar flares in hard X-rays. Title: Nonthermal Flare Emission from MeV-Energy Electrons at 17, 34, and 86, GHz Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T. Bibcode: 2000ASPC..206..307K Altcode: 2000hesp.conf..307K No abstract at ADS Title: Radio Emissions from the Sun's Corona Authors: Kundu, Mukul R. Bibcode: 2000IAUJD...7E...6K Altcode: A review of recent observations of coronal radio emissions will be presented, with particular reference to flares and weak coronal transients, and their relationships to emissions in other spectral domains.The radio emissions to be discussed are obtained with large radio interferometers such as the Very Large Array (VLA) in USA,the Nobeyama Radio Heliograph (NoRH) in Japan,the Berkeley-Illinois-Maryland Millimeter Array (BIMA), and the Nancay(France) metric radio heliograph. Selected imaging observations of solar flares and transients at all wavelengths will be emphasized, providing information on the structure and spatial location of flaring radio sources with respect to flaring soft X-ray loops and hard X-ray sources. Observational evidence will be presented on acceleration of electrons to MeV energies and of the existence of different energetic electron populations in solar flares. Title: Millimeter-Interferometer Observations of Flares in Conjunction with HESSI Authors: White, S. M.; Kundu, M. R. Bibcode: 2000ASPC..206..335W Altcode: 2000hesp.conf..335W No abstract at ADS Title: Observations and Models of a Flaring Loop Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E. Bibcode: 2000ASPC..206..359N Altcode: 2000hesp.conf..359N No abstract at ADS Title: Two-Temperature Coronal Models from SOHO/EIT Observations Authors: Zhang, J.; White, S. M.; Kundu, M. R. Bibcode: 1999ApJ...527..977Z Altcode: We present a method for deriving a two-thermal-component approximation to the differential emission measure distribution of plasma in the Sun's corona in the temperature range to which the Extreme-Ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO) spacecraft is sensitive. EIT takes high-resolution full-disk coronal images in three of its four optimized channels by observing emission lines of highly ionized Fe whose formation temperatures overlap and cover the range from 0.7 to 2.8 MK. It is straightforward to show that the traditional single-temperature models based on the ratio of a pair of EIT images at different wavelengths are not able adequately to represent the plasma contributing to all three wavelength ranges. In this paper, we develop a modified image-ratio method that results in a two-thermal-component model for the plasma producing the coronal emission observed by EIT. The products of this method are two temperature and two emission measure full-disk maps of the Sun's corona, with the full resolution of the EIT telescope, in two temperature regimes: one from 0.8 to 1.6 MK and the other from 1.6 to 2.6 MK. The two-component solutions are tested using a series of model differential emission measures (DEMs) from the CHIANTI atomic database package. This method appears to produce realistic results in all regions of the Sun's atmosphere with the exception of coronal holes, where very cool Si VII/Mg VII lines (<0.7 MK) contribute more to the EIT 284 Å image than the otherwise dominant hot Fe XV lines and result in unrealistically high temperatures for the hot component there. We demonstrate that while the raw EIT images are dominated by the spatial distribution of emission measure in the corona, the temperature maps often emphasize fine structure, which is less visible in the flux images. The emission measure of the hot component is always larger than that of the cool component. On the disk there appears to be a firm lower limit to the integrated column emission measure along any line of sight, including toward coronal holes. There is no overall correlation between temperature and emission measure. Title: Microwave and Extreme Ultraviolet Observations of Solar Polar Regions Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.; Shibasaki, K.; Dere, K. P. Bibcode: 1999ApJ...527..415N Altcode: The poles of the Sun are brighter than the rest of the quiet Sun's emission in a limited range of radio frequencies from 17 GHz to 87 GHz. We have studied microwave images of the quiet Sun made with the Nobeyama radioheliograph at 17 GHz. They show that the so-called polar-cap brightening consists of two components: a diffuse component of 1500 K excess brightness and patchy compact sources with localized excess brightness of about 3500 K. We test the reality of the compact sources using the maximum entropy method deconvolution. The total flux and the number of compact polar sources as well as the north-south extent of the diffuse polar emission are larger in the pole that is closest to the Earth. We compared the microwave polar emission with nearly simultaneous SOHO EIT images taken in the lines of He II at 304 Å and Fe XII at 195 Å. No one-to-one correlation between the compact radio sources and the bright EUV features was found: most of the radio emission arises between the plumes visible to EIT. The boundaries of the polar-cap brightenings did not match exactly the boundaries of the coronal holes as seen in either the Fe XII 195 Å images or the He II 304 Å images. The temporal variations of the compact microwave sources did not correspond to any significant changes in EUV emission. On the other hand, most He II 304 Å changing features were associated with the diffuse polar microwave emission, which was practically constant. Our data suggest that the origin of the polar brightening is not coronal; it seems that the bulk of the patchy radio emission comes from heights below the 80,000 K layer. Title: A Microwave Study of Coronal and Chromospheric Ejecta Authors: Nindos, A.; Kundu, M. R.; Raulin, J. -P.; Shibasaki, K.; White, S. M.; Nitta, N.; Shibata, K.; Shimojo, M. Bibcode: 1999spro.proc..135N Altcode: We have studied the radio properties of 18 X-ray coronal jets (observed by the Yohkoh SXT) using Nobeyama 17 GHz data. We also searched for chromospheric ejecta (Hα surges) during the time intervals that the X-ray images were available. Microwave emission was associated with the majority of the X-ray jets. The radio emission came from the base or the lower part of the jets. We detected radio emission from almost all jets which showed flare-like activity at their footpoints. The 17 GHz time profiles were gradual and unpolarized, implying that the emission was thermal. When possible, we computed the physical properties of the X-ray-emitting ejected plasma. In one two-sided-loop type jet and one anemone-type jet, the observed microwave fluxes from the lower part of the jets were well above the fluxes predicted from the computed electron temperatures and emission measures of the soft X-ray-emitting material on the basis of thermal free-free emission. We interpreted the large discrepancies in terms of the presence of lower temperature material which cannot be detected by the SXT but produces strong microwave free-free emission. This is the first time that such material is observed in two-sided-loop type jets. Thus our observations confirm the theoretical prediction by Yokoyama and Shibata (1996). We detected no cool material at the base of the jets. We also observed an Hα surge which was not associated with an X-ray jet and showed no signatures on the SXT images but was detected with the Nobeyama Radioheliograph. The emission of the microwave surge-associated source was free-free from the chromospheric plasma. Constraints for the surge density were derived. Title: Solar Flare Physics Authors: Schmahl, Edward J.; Kundu, Mukul R. Bibcode: 1999STIN...0025246S Altcode: We have continued our previous efforts in studies of fourier imaging methods applied to hard X-ray flares. We have performed physical and theoretical analysis of rotating collimator grids submitted to GSFC for the HESSI (High Energy Solar Spectroscopic Imager) mission involving the imaging of solar flares in hard X-rays. In the following pages we present analysis of several different imaging techniques, and focus on the one (The Polar Representation) that shows the greatest promise in minimizing storage requirements and maximizing the speed of map making. Title: Active Region Emissions and Coronal Field Extrapolations Authors: Lee, J.; White, S. M.; Kundu, M. R.; Mikic, Z. Bibcode: 1999spro.proc...65L Altcode: With vector magnetographs set to fly on the Solar--B mission, the extrapolation of photospheric magnetic fields into the corona will be increasingly important. As the techniques of coronal field extrapolations grow more sophisticated, we require a more powerful means to test them and to make full use of the information they contain. Radio data can play an important role in testing extrapolation methods. In this paper, we discuss a new test of coronal field extrapolation using the concept of field line connectivity. The motivating idea is that temperature should be nearly uniform on a given magnetic field line due to the rapid transport of physical quantities along field lines in the corona. Optically--thick gyroresonance emission provides the temperature on a surface of known magnetic field strength in the corona. As a consequence, we may expect that radio intensities observed at different frequencies at points connected by field lines should show a good correlation. This suggests that a test of a magnetic field extrapolation model is whether the field--line connectivity it predicts shows such a correlation. A second application of field--line connectivity is to try to understand the relationship between physical quantities in the photosphere at the footpoints of magnetic field lines and the heating process in the corona on the same field lines. If a particular magnetic quantity, such as shear, plays a role in coronal heating then one expects the coronal extension of field lines passing through peaks in this quantity will show the highest coronal temperatures. This idea can be used to test candidate coronal heating mechanisms. We demonstrate these ideas using the combination of high--resolution VLA observations of a complex active region together with state--of--the--art nonlinear force--free field modeling. Title: Radio Observations of Weak Coronal Transients Authors: Kundu, M. R. Bibcode: 1999spro.proc..111K Altcode: In this review we discuss radio observations of weak coronal transients. We concentrate on the transient events observed primarily by Yohkoh/SXT and to a smaller extent by SOHO/EIT. The radio observations are those obtained with the Very Large Array (VLA) in microwaves, the Nancay (France) metric radioheliograph at 150 - 450 MHz and the Nobeyama RadioHeliograph (NRH) at 17 GHz. We discuss the observational characteristics of X-ray bright point flares at meter wavelengths and in microwaves, and provide evidence that both thermal and nonthermal processes occur in these small scale flaring events. Similarly, radio observations of X-ray jets in microwaves and at meter wavelengths provide evidence for both thermal and nonthermal processes in these dynamic coronal phenomena. Nonthermal radio emission in the form of metric type III bursts is produced by electron beams propagating along the jet, whereas microwave emission comes mostly from the jet base. We discuss active region transient brightenings (ARTB's) and show that their radio emission can be purely thermal, thermal gyro- resonance or nonthermal gyrosynchrotron radiation. We discuss one form (radio-selected) of quiet Sun transient brightenings located far from active regions. We provide evidence that weak plasma ejections following flares is observed at metric wavelengths in the form of transient continuum emission. Finally, we discuss the time-varying polar brightenings at 17 GHz, and their relationship to polar erupting plumes observed by SOHO-EIT. Title: Multiple Components in the Millimeter Emission of a Solar Flare Authors: Raulin, J. -P.; White, S. M.; Kundu, M. R.; Silva, A. V. R.; Shibasaki, K. Bibcode: 1999ApJ...522..547R Altcode: We analyze a small flare using imaging data at millimeter, microwave, and soft X-ray wavelengths and microwave and hard X-ray spectral observations. The remarkable aspect of this flare is evidence for the presence of MeV-energy electrons, which are responsible for the nonthermal millimeter emission, at a time when no hard X-rays from lower energy electrons are detected. This occurs during a smoothly varying phase, which is seen at radio wavelengths to last several minutes and is the brightest phase at millimeter wavelengths but is undetected in hard X-rays: it follows a brief spike of emission at flare onset, which has the more usual properties of impulsive events and features nonthermal microwave, millimeter, and hard X-ray emission. We interpretthe phase that is brightest at millimeter wavelengths as being due to efficient trapping of a relatively small number of nonthermal electrons, whereas during the hard X-ray emission, trapping is much less efficient, and the decay time is much shorter at all energies, which leads to a larger ratio of hard X-ray flux to radio flux. As in many previous events studied at millimeter wavelengths, there is a discrepancy between the electron energy spectral indices inferred from the milllimeter and hard X-ray data during the impulsive phase when both are detected: again it appears that the energy spectrum at 1 MeV must be significantly flatter than at several hundred keV and below. However, there are problems in reconciling quantitatively the energy spectra for the hard X-ray-emitting and radio-emitting components: based on the most plausible parameters, the radio-emitting electrons should produce most of the hard X-rays. One solution to this contradiction is to invoke a coronal magnetic field stronger than seems likely based on the photospheric magnetic field. Title: Radio and X-Ray Imaging Observations of a Continuum Burst Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.; Raoult, A. Bibcode: 1999ApJ...522.1100K Altcode: We study a metric continuum burst observed on 1993 February 18, and its X-ray signatures from imaging observations in radio and X-rays using the Nançay radioheliograph and the Yohkoh Soft X-Ray Telescope (SXT). The event in question was associated with weak type III bursts; these were detected at only one frequency (164 MHz), except for one burst (at 10:58:05 UT), which was observed over a broad frequency range (164-435 MHz). We believe that the early metric continuum burst is an extension of the microwave continuum which was observed at frequencies as high as 5 GHz, and its onset at ~10:50 UT is associated with the development of an X-ray-emitting diffuse loop system which appears to advance with a speed of ~50-100 km s-1. The observed type III bursts seem to correspond to the repeated occurrence/appearance of a collimated jet emanating from the loop system that is responsible for the continuum burst. A few minutes prior to the main continuum onset there is a soft X-ray ejection from the main flare region. The main continuum has a brightness temperature greater than 108 K; it is unpolarized, and it shows dispersion in position with frequency and moves with speeds of ~50 km s-1 at 236-410 MHz. The SXT images reveal that this initially ejected soft X-ray-emitting hot plasma seems to gradually fill up the loop system with hot material. This hot plasma must contain enough energetic electrons of energy greater than several tens of keV, which are responsible for producing the metric continuum burst by plasma radiation mechanism. Title: A Microwave Study of Coronal Ejecta Authors: Kundu, M. R.; Nindos, A.; Raulin, J. -P.; Shibasaki, K.; White, S. M.; Nitta, N.; Shibata, K.; Shimojo, M. Bibcode: 1999ApJ...520..391K Altcode: Using Nobeyama 17 GHz data, we have studied the radio properties of 19 coronal jets identified in Yohkoh soft X-ray imaging telescope (SXT) X-ray observations. The radio data provide information on the physical conditions in the jets, which complements the data from the X-ray surveys. Microwave emission was associated with the majority of the X-ray jets in our sample. The radio emission typically came from the base or the base and lower part of the jets. We detected radio emission from almost all jets that showed flarelike activity at their bases. The jets that were not associated with radio emission did not show any significant increase in X-ray emission at their bases. The strongest radio emission came from two of the largest jets in our sample. Our data show a general correlation between the X-ray jet fluxes and the associated radio fluxes. The 17 GHz time profiles were gradual and unpolarized, implying that the emission was thermal. In a two-sided-loop jet (1992 July 22 event) and one anemone-type jet (1993 February 9 event), the observed microwave fluxes from the lower part of the jets were well above the fluxes calculated from the computed physical parameters of the soft X-ray-emitting material on the basis of thermal free-free emission. We interpret the large discrepancies in terms of the presence of lower temperature material, which cannot be detected by the SXT (the SXT is most sensitive to hot plasma above 2×106 K), but which produces strong microwave free-free emission. This is the first time that such material has been observed in two-sided-loop-type jets. We also observed motion of a jet-associated microwave source with a velocity of 55 km s-1. The microwave motion occurred after the appearance of the X-ray jet. There is clear evidence that the microwave emission of that source was associated with the jet and not with the associated small flare. Title: Microwave and Extreme Ultraviolet Observations of Solar Polar Regions Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.; Shibasaki, K.; Dere, K. P. Bibcode: 1999AAS...194.3207N Altcode: 1999BAAS...31..871N The radio emission of solar poles is brighter than the rest of the quiet Sun's emission in a limited range of frequencies from 17 GHz to 87 GHz. We have studied microwave images of the quiet Sun made with the Nobeyama Radioheliograph at 17 GHz. They show that the so-called polar-cap brightening consists of two components: a diffuse component of 1500 K excess brightness, and patchy compact sources with localized excess brightness of about 3500 K. The total flux and the number of compact polar sources as well as the North-South extent of the diffuse polar emission are larger in the pole which is closest to the Earth. We compared the microwave polar emission with nearly simultaneous SoHO EIT images taken in the lines of He ii at 304 Angstroms and Fe xii at 195 Angstroms. No one-to-one correlation between the compact radio sources and the bright EUV features was found: most of the radio emission arises between the plumes visible to EIT. The boundaries of the polar-cap brightenings did not match exactly the boundaries of the coronal holes as seen in the Fe xii 195 Angstroms images. The temporal variations of the compact microwave sources did not correspond to any significant changes in EUV emission. On the other hand, most He ii 304 Angstroms changing features were associated with the diffuse polar microwave emission which was practically constant. Our data suggest that the origin of the polar brightening is not coronal; it seems that the bulk of the patchy radio emission comes from heights below the 80000 K layer. Title: A Microwave Study of Coronal Ejecta Authors: Kundu, M. R.; Nindos, A.; Raulin, J. -P.; Shibasaki, K.; White, S. M.; Nitta, N.; Shibata, K.; Shimojo, M. Bibcode: 1999AAS...194.1704K Altcode: 1999BAAS...31..853K Using Nobeyama 17 GHz data, we have studied the radio properties of 19 coronal jets identified in Yohkoh SXT X-ray observations. The radio data provide information on the physical conditions in the jets which complements the data from the X-ray surveys. Microwave emission was associated with the majority of the X-ray jets in our sample. The radio emission typically came from the base or the base and lower part of the jets. We detected radio emission from almost all jets which showed flare-like activity at their bases. The jets which were not associated with radio emission did not show any significant increase in X-ray emission at their bases. The strongest radio emission came from two of the largest jets in our sample. Our data show a general correlation between the X-ray jet fluxes and the associated radio fluxes. The 17 GHz time profiles were gradual and unpolarized, implying that the emission was thermal. In a two-sided-loop jet (July 22, 1992 event) and one anemone-type jet (February 9, 1993 event), the observed microwave fluxes from the lower part of the jets were well above the fluxes calculated from the computed physical parameters of the soft X-ray-emitting material on the basis of thermal free-free emission. We interpret the large discrepancies in terms of the presence of lower temperature material which cannot be detected by the SXT (the SXT is most sensitive to hot plasma above 2 x 10(6) K) but which produces strong microwave free-free emission. This is the first time that such material has been observed in two-sided-loop type jets. We also observed motion of a jet-associated microwave source with a velocity of 55 km/sec. The microwave motion occurred after the appearance of the X-ray jet. There is clear evidence that the microwave emission of that source was associated with the jet and not with the associated small flare. Title: The Sun's Corona viewed from EUV and Radio Wavelengths Authors: Zhang, J.; Kundu, M. R.; White, S. W. Bibcode: 1999AAS...194.1608Z Altcode: 1999BAAS...31..851Z The Sun's Corona, which is composed of a few million degree plasma, can be best viewed in two electro-magnetic wavelength domains, one from a few Angstrom to hundreds of Angstrom (in Soft X-ray and EUV domains), the other from a few centimeter to several tens of centimeter wavelengths (in radio domain). In this paper, we present the detailed and quantitative comparison of corona observations made in these two domains with high spatial resolution and full view of the Sun. The EUV observations were taken with EIT (Extreme Ultraviolet Imager) on board SOHO (Solar and Heliospheric Observatory) in Fe spectral lines centered at 171, 195 and 284 Angstrom, respectively; while the radio observations were taken with the VLA (Very Large Array) at 6 and 20 cm, and NRH (Nobeyama Radio Heliograph) at 1.8 cm (17 Ghz), respectively. We have found that there exists excellent morphological similarity of corona features between these two sets of observations. However, the quantitative comparisons have revealed that the predicted radio flux from EUV observations based on traditional assumptions is always higher than that observed directly by radio instruments, by a factor of 4 to 6. The discrepancy is probably due to the underestimation of coronal ion abundance (e.g. Meyer's abundance) by a factor of 4 to 6. Title: Millimeter Imaging Observations of High Energy Electrons in Solar Flares Authors: White, S. M.; Kundu, M. R. Bibcode: 1999AAS...194.8009W Altcode: 1999BAAS...31..966W The 10-element BIMA array will be used in to image solar flares at millimeter wavelengths during campaign periods in the upcoming solar maximum. Since millimeter emission in the impulsive phase of flares comes from electrons with energies typically in excess of 1 MeV, these observations complement observations of lower energy electrons at other wavelengths. Recent BIMA flare data will be presented and plans for the near future will be discussed. Title: A Study of Microwave-selected Coronal Transient Brightenings Authors: Nindos, A.; Kundu, M. R.; White, S. M. Bibcode: 1999ApJ...513..983N Altcode: We present the results of a search for radio-selected transient brightenings (TBs) in the solar atmosphere as a complement to the more common X-ray-selected surveys. The Sun was generally quiet during the observations, making these data sensitive to weak TBs both in and outside active regions. Five small impulsive events were identified in a set of VLA observations at 4.5, 1.5, and 0.33 GHz and compared with soft X-ray images from Yohkoh and EUV images from SOHO/EIT. Four of the events were located at the edges of an active region, but one was located 100" away in a quiet region of the atmosphere. Possible emission mechanisms for these brightenings are investigated. The time profiles of the radio TBs show impulsive peaks, while the corresponding soft X-ray profiles are gradual. The impulsive radio peaks were up to 35% polarized. Our data favor an interpretation in terms of gyrosynchrotron radiation from mildly relativistic electrons. A small number of nonthermal electrons with spectral index 3 can explain the observed properties of the TBs. Thus, nonthermal TBs can be found away from active regions. Two of the microwave TBs also show evidence for type III radio emission at 327 MHz. Title: A Test for Coronal Magnetic Field Extrapolations Authors: Lee, Jeongwoo; White, Stephen M.; Kundu, Mukul R.; Mikić , Zoran; McClymont, A. N. Bibcode: 1999ApJ...510..413L Altcode: As models for the physical properties of the corona above solar active regions grow more sophisticated, we will require better means for testing them. In this paper we discuss and apply such a test to a magnetic field model for an active region. This test is based on the expectation that the temperatures at different points on a given magnetic field line should be well correlated because of the rapid transport of heat along field lines in the corona. We use radio observations of an active region to measure the temperatures on field lines as they cross two isogauss surfaces (at 430 and 750 G) in the corona. The field lines and isogauss surfaces are derived from a coronal magnetic field model obtained via a nonlinear force-free field extrapolation of a photospheric vector magnetogram; for comparison, we also investigate a potential-field extrapolation of the same magnetogram. In a region in which strongly sheared fields are present, the nonlinear force-free field model does indeed show a good correlation between the temperatures in the two surfaces at points on the same field line, while the potential-field model does not. This diagnostic acts both as a test of the magnetic field model as well as of the interpretation of the radio data, and we show how this test can also aid in understanding the radio data. Title: University of Maryland, Department of Astronomy, College Park, Maryland 20742. Report for the period 1 Oct 1997 - 30 Sep 1998. Authors: Kundu, M. R. Bibcode: 1999BAAS...31..194K Altcode: No abstract at ADS Title: Solar Flare Physics Authors: Schmahl, Edward J.; Kundu, Mukul R. Bibcode: 1998STIN...9914342S Altcode: We have continued our previous efforts in studies of fourier imaging methods applied to hard X-ray flares. We have performed physical and theoretical analysis of rotating collimator grids submitted to GSFC(Goddard Space Flight Center) for the High Energy Solar Spectroscopic Imager (HESSI). We have produced simulation algorithms which are currently being used to test imaging software and hardware for HESSI. We have developed Maximum-Entropy, Maximum-Likelihood, and "CLEAN" methods for reconstructing HESSI images from count-rate profiles. This work is expected to continue through the launch of HESSI in July, 2000. Section 1 shows a poster presentation "Image Reconstruction from HESSI Photon Lists" at the Solar Physics Division Meeting, June 1998; Section 2 shows the text and viewgraphs prepared for "Imaging Simulations" at HESSI's Preliminary Design Review on July 30, 1998. Title: The Height Structure of the Solar Atmosphere from the Extreme-Ultraviolet Perspective Authors: Zhang, Jie; White, S. M.; Kundu, M. R. Bibcode: 1998ApJ...504L.127Z Altcode: 1998astro.ph..7175Z We investigate the structure of the solar chromosphere and transition region using full Sun images obtained with the Extreme-Ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory spacecraft. The limb seen in the EIT coronal images (taken in lines of Fe IX/X at 171 Å, Fe XII at 195 Å, and Fe XV at 284 Å) is an absorption limb predicted by models to occur at the top of the chromosphere where the density of neutral hydrogen becomes significant (~1010 cm-3). The transition-region limb seen in He II λ304 images is an emission limb. We find that (1) the limb is higher at the poles than at the equator both in the coronal images (by 1300+/-650 km) and the 304 Å images (by 3500+/-1200 km), and (2) the 304 Å limb is significantly higher than the limb in the coronal images. The height difference is 3100+/-1200 km at the equator and 6600+/-1200 km at the poles. We suggest that the elevation of the 304 Å limb above the limb in the coronal images may be due to the upper surface of the chromosphere being bumpy, possibly because of the presence of spicules. The polar extension is consistent with a reduced heat input to the chromosphere in the polar coronal holes compared with the quiet-Sun atmosphere at the equator. Title: Coronal Currents, Magnetic Fields, and Heating in a Solar Active Region Authors: Lee, Jeongwoo; McClymont, A. N.; Mikić, Zoran; White, Stephen M.; Kundu, Mukul R. Bibcode: 1998ApJ...501..853L Altcode: We compare microwave images of a solar active region with state-of-the-art fully nonlinear force-free extrapolations of the photospheric fields in order to study the link between coronal currents and heating of the corona. This extrapolation fully takes into account the nonuniform distribution of electric currents observed in the photosphere and its role in the coronal magnetic structure. We carry out the comparison for AR 6615, a complex region observed with the VLA on 1991 May 7. Under the assumption that the microwave emission is dominated by optically thick gyroresonance radiation, we may use the radio images to infer the temperature of the corona at different heights and locations. This is then compared with heating models based on the observed current distribution. We are able to reproduce the radio images remarkably well with a model in which temperature is structured along magnetic field lines, depends on the current on the field line, and increases with height in a manner similar to that inferred from static heated loop models. This result implies a direct link between electric currents and coronal heating. Title: Spatial Structure of Solar Coronal Magnetic Loops Revealed by Transient Microwave Brightenings Authors: Zhang, J.; Gopalswamy, N.; Kundu, M. R.; Schmahl, E. J.; Lemen, J. R. Bibcode: 1998SoPh..180..285Z Altcode: We present the measurement of magnetic field gradient in magnetic loops in the solar corona, based on the multi-wavelength Very Large Array observations of two transient microwave brightenings (TMBs) in the solar active region 7135. The events were observed at 2 cm (spatial resolution ∼ 2=) and 3.6 cm (spatial resolution ∼ 3=) with a temporal resolution of 3.3 s in a time-sharing mode. Soft X-ray data (spatial resolution ∼ 2.5=) were available from the Soft X-ray Telescope on board the Yohkoh satellite. The three-dimensional structure of simple magnetic loops, where the transient brightenings occurred, were traced out by these observations. The 2-cm and 3.6-cm sources were very compact, located near the footpoint of the magnetic loops seen in the X-ray images. For the two events reported in this paper, the projected angular separation between the centroids of 2 and 3.6-cm sources is about 2.3= and 3.1=, respectively. We interpret that the 2 and 3.6-cm sources come from thermal gyro-resonance emission. The 2-cm emission is at the 3rd harmonic originating from the gyro-resonance layer where the magnetic field is 1800 G. The 3.6-cm emission is at the 2nd harmonic, originating from the gyro-resonance layer with a magnetic field of 1500 G. The estimated magnetic field gradient near the footpoint of the magnetic loop is about 0.09 G km=1 and 0.12 G km=1 for the two events. These values are smaller than those observed in the photosphere and chromosphere by at least a factor of 2. Title: Microwave Mode Coupling Above Active Regions as a Coronal Density Diagnostic Authors: Lee, Jeongwoo; White, Stephen M.; Kundu, M. R.; Mikić, Zoran; McClymont, A. N. Bibcode: 1998SoPh..180..193L Altcode: It is well recognized that the phenomenon of depolarization (the conversion of polarized radio emission into unpolarized emission) of microwaves over solar active regions can be used to infer the coronal electron density once the coronal magnetic field is known. In this paper we explore this technique using an active region for which we have excellent radio data showing depolarization at two frequencies, and for which we have an excellent magnetic field model which has been tested against observations. We show that this technique for obtaining coronal densities is very sensitive to a number of factors. When Cohen's (1960) theory where depolarization is due to magnetic field rotation alone is used, the result is particularly sensitive to the location of the surface on which the magnetic field is orthogonal to the line of sight. Depending on whether we take into account the presence of electric currents in the photosphere or not, their extrapolation into the corona can result in very different heights being deduced for the location of the depolarization strip, and this changes the density which is then deduced from the depolarization condition. Such extreme sensitivity to the magnetic field model requires that field extrapolations be able to accurately predict the polarity of magnetic fields up to coronal heights as high as ∼ 105 km in order to exploit depolarization as a density diagnostic. Title: Microwave and Soft X-ray Study of Solar Active Region Evolution Authors: Lara, A.; Gopalswamy, N.; Kundu, M. R.; Pérez-Enríquez, R.; Koshiishi, H.; Enome, S. Bibcode: 1998SoPh..178..353L Altcode: We have studied the properties and evolution of several active regions observed at multiple wavelengths over a period of about 10 days. We have used simultaneous microwave (1.5 and 17 GHz) and soft X-ray measurements made with the Very Large Array (VLA), the Nobeyama Radio Heliograph (NRH) and the Soft X-ray Telescope (SXT) on board the Yohkoh spacecraft, as well as photospheric magnetograms from KPNO. This is the first detailed comparison between observations at radio wavelengths differing by one order of magnitude. We have performed morphological and quantitative studies of active region properties by making inter-comparison between observations at different wavelengths and tracking the day-to-day variations. We have found good general agreement between the 1.5 and 17 GHz radio maps and the soft X-rays images. The 17 GHz emission is consistent with thermal bremsstrahlung (free-free) emission from electrons at coronal temperatures plus a small component coming from plasma at lower temperatures. We did not find any systematic limb darkening of the microwave emission from active regions. We discuss the difference between the observed microwave brightness temperature and the one expected from X-ray data and in terms of emission of a low temperature plasma at the transition region level. We found a coronal optical thickness of ∼ 10-3 and ∼ 1 for radiation at 17 and 1.5 GHz, respectively. We have also estimated the typical coronal values of emission measure (∼ 5 × 1028 cm-5), electron temperature (∼ 4.5 × 1066 K) and density (∼ 1.2 × 109 cm3). Assuming that the emission mechanism at 17 GHz is due to thermal free-free emission, we calculated the magnetic field in the source region using the observed degree of polarization. From the degree of polarization, we infer that the 17 GHz radiation is confined to the low-lying inner loop system of the active region. We also extrapolated the photospheric magnetic field distribution to the coronal level and found it to be in good agreement with the coronal magnetic field distribution obtained from microwave observations. Title: Two-Sided-Loop Type X-ray Jets and Metric Radio Bursts Authors: Kundu, M. R.; Raulin, J. -P.; Nitta, N.; Shibata, K.; Shimojo, M. Bibcode: 1998SoPh..178..173K Altcode: 1998SoPh..178..611K We have searched for nonthermal radio signatures in the form of metric type III bursts in conjunction with two-sided-loop-type X-ray jets observed by the Yohkoh/SXT experiment. We have found no evidence of type III bursts in association with this particular type of X-ray jets in contrast to the positive evidence of type III's in association with anemone-type X-ray jets. This result is consistent with the simulation results of Yokoyama and Shibata (1995), which show that anemone-type jets are produced by vertical/oblique plasma flow whereas the two-sided-loop-type jets are produced by horizontal plasma flow. Title: The Emergence of a Solar Active Region Authors: White, S. M.; Lee, J.; Kundu, M. R.; SOHO/MDI Team Bibcode: 1998ASPC..155..130W Altcode: 1998sasp.conf..130W No abstract at ADS Title: Type-III metric and microwave burst observations of coronal X-ray jets Authors: Kundu, M. Bibcode: 1998ESASP.421..179K Altcode: 1998sjcp.conf..179K No abstract at ADS Title: The Solar Atmosphere Above a Sunspot Authors: Zlotnik, E. Ya.; White, S. M.; Kundu, M. R. Bibcode: 1998ASPC..155..135Z Altcode: 1998sasp.conf..135Z No abstract at ADS Title: Synoptic Radio Observations Authors: Schmahl, E. J.; Kundu, M. R. Bibcode: 1998ASPC..140..387S Altcode: 1998ssp..conf..387S No abstract at ADS Title: University of Maryland, Department of Astronomy, College Park, Maryland 20742. Report for the period 1 Oct 1996 - 30 Sep 1997. Authors: Kundu, M. R. Bibcode: 1998BAAS...30..233K Altcode: No abstract at ADS Title: A Search for Hard X-ray Emission from Active Stars Using CGRO/BATSE Authors: White, S. M.; Harmon, B. A.; Lim, J.; Kundu, M. R. Bibcode: 1998ASPC..154.1192W Altcode: 1998csss...10.1192W We report the results of a search for > 20 keV photons from active stars using CGRO/BATSE Earth-occultation observations. Twelve of the "usual suspects" together with 12 "placebo" locations have been analyzed using the BATSE software for occultation analysis developed at NASA/MSFC. There are four detections at the nominal 5sigma level, and eight at the 3sigma level. However the strongest detection (that of AB Dor) shows clear evidence for contamination from the nearby strong source LMC X-4. 18 of the 24 fields yield positive fluxes, indicating a clear bias in the results, and possibly indicating the presence of weak background hard X-ray sources detectable by BATSE in long-term studies. Title: Fast Time Structure during Transient Microwave Brightenings: Evidence for Nonthermal Processes Authors: Gopalswamy, N.; Zhang, J.; Kundu, M. R.; Schmahl, E. J.; Lemen, J. R. Bibcode: 1997ApJ...491L.115G Altcode: 1997astro.ph.10200G Transient microwave brightenings (TMBs) are small-scale energy releases from the periphery of sunspot umbrae with a flux density 2 orders of magnitude smaller than that from a typical flare. Gopalswamy et al. first reported the detection of the TMBs, and it was pointed out that the radio emission implied a region of very high magnetic field so that the emission mechanism has to be gyroresonance or nonthermal gyrosynchrotron, but not free-free emission. It was not possible to decide between gyroresonance and gyrosynchrotron processes because of the low time resolution (30 s) used in the data analysis. We have since performed a detailed analysis of the Very Large Array data with full time resolution (3.3 s) at two wavelengths (2 and 3.6 cm), and we can now adequately address the question of the emission mechanism of the TMBs. We find that nonthermal processes indeed take place during the TMBs. We present evidence for nonthermal emission in the form of temporal and spatial structure of the TMBs. The fast time structure cannot be explained by a thermodynamic cooling time and therefore requires a nonthermal process. Using the physical parameters obtained from X-ray and radio observations, we determine the magnetic field parameters of the loop and estimate the energy released during the TMBs. The impulsive components of TMBs imply an energy release rate of ~1.3×1022 ergs s-1, so the thermal energy content of the TMBs could be less than ~1024 ergs. Title: Detection of Microwave Emission from Coronal X-Ray Jets Authors: Kundu, M. R.; Shibasaki, K.; Nitta, N. Bibcode: 1997ApJ...491L.121K Altcode: We present evidence of the detection of microwave emission at 17 GHz in association with coronal X-ray jets. We present two typical cases--one on the disk (1995 March 31) and the other at the limb (1992 August 25). For the disk event we see 17 GHz emission from the upper part of the jet base (active region loop or loops), but no emission from the collimated X-ray jet itself, implying that it must be optically thin at 17 GHz. For the limb event, we see the base of the jet as well as the bottom part of the jet itself, implying that the optical depth is higher at the bottom part (obviously because of higher electron density) than at the top. We believe that the 17 GHz emission is thermal, because it is gradual and unpolarized, and that the heating process that gives rise to the jet X-ray plasma also results in the 17 GHz emission. The calculated 17 GHz flux densities seem to agree with the observed values within a factor of 2. We consider this disagreement to be quite reasonable in view of the various uncertainties involved in computing the emission in both radio and X-rays. Title: X-Ray and Radio Studies of a Coronal Eruption: Shock Wave, Plasmoid, and Coronal Mass Ejection Authors: Gopalswamy, N.; Kundu, M. R.; Manoharan, P. K.; Raoult, A.; Nitta, N.; Zarka, P. Bibcode: 1997ApJ...486.1036G Altcode: On 1994 July 31, a fast (900 km s-1) eruptive structure was observed in X-rays, followed by a slower plasmoid (180 km s-1). They were associated with a coronal mass ejection, prominence eruption, and a host of metric radio bursts. The X-ray structure seems to be a part of a white light coronal mass ejections (CME), as inferred from the white light images of July 30 and 31. A type II burst was observed at the leading edge of the X-ray eruption, while a type IV burst was spatially associated with the detached plasmoid. The type III radio bursts occurred on thin overdense structures associated with the eruption. We detected the rise of plasma levels because of mass addition to the type III burst sources as a result of the eruption. This event further clarifies the manifestation of a CME in X-rays. We identify the X-ray eruption as the driver of the coronal shock wave. This provides answer to the long-standing question regarding the origin of coronal and interplanetary shock waves. We have also found evidence to support the idea that herringbone bursts are produced when the coronal shock wave crosses open magnetic field lines. Title: Radio Observations of Gyroresonance Emission from Coronal Magnetic Fields Authors: White, S. M.; Kundu, M. R. Bibcode: 1997SoPh..174...31W Altcode: We review the basic characteristics of thermal gyroresonance (also known as cyclotron) emission from solar active regions, and show how radio observations combined with our understanding of the basic mechanism can reveal much of the magnetic and thermal structure of the corona over active regions. Title: Signatures of Coronal Currents in Microwave Images Authors: Lee, Jeongwoo; White, Stephen M.; Gopalswamy, N.; Kundu, M. R. Bibcode: 1997SoPh..174..175L Altcode: Microwave emission from solar active regions at frequencies above 4 GHz is dominated by gyroresonance opacity in strong coronal magnetic fields, which allows us to use radio observations to measure coronal magnetic field strengths. In this paper we demonstrate one powerful consequence of this fact: the ability to identify coronal currents from their signatures in microwave images. Specifically, we compare potential-field (i.e., current-free) extrapolations of photospheric magnetic fields with microwave images and are able to identify regions where the potential extrapolation fails to predict the magnetic field strength required to explain the microwave images. Comparison with photospheric vector magnetic field observations indicates that the location inferred for coronal currents agrees with that implied by the presence of vertical currents in the photosphere. The location, over a neutral line exhibiting strong shear, is also apparently associated with strong heating. Title: Solar Flare Physics Authors: Schmahl, Edward J.; Kundu, Mukul R. Bibcode: 1997umd..rept.....S Altcode: 1997STIN...9892889S We have continued our previous efforts in studies of fourier imaging methods applied to hard X-ray flares. We have performed physical and theoretical analysis of rotating collimator grids submitted to GSFC for future space or suborbital missions involving the imaging of solar flares in hard X-rays. In particular, we have simulated the performance of the High Energy Solar Spectroscopic Imager (HESSI), using pseudo-flare images provided. We have computed count rates that HESSI would record for these simulated flares, and reconstructed images from the count rates. Title: Modeling of a Microwave Burst Emission Authors: Preka-Papadema, P.; Alissandrakis, C. E.; Dennis, B. R.; Kundu, M. R. Bibcode: 1997SoPh..172..233P Altcode: 1997ESPM....8..233P We applied model computations on a microwave burst observed with the Westerbork Synthesis Radio Telescope (WSRT) at 6 cm. We used additional data from Hα, soft and hard X-rays in order to reproduce the flaring loop and to compute the microwave total intensity and circular polarization. We examined both cases of thin and thick target. The computations show a large emission source in an optically thick loop. We compare our results with the observation. Title: Radio Observations of the Emergence of a Solar Active Region Authors: White, S. M.; Lee, J.; Kundu, M. R. Bibcode: 1997SPD....28.0603W Altcode: 1997BAAS...29..910W On July 6 1996 a solar active region abruptly began to emerge through the solar photosphere. This region was eventually to produce the first X-class flare since 1993. We happened to be observing the region with the VLA during its emergence, and present a preliminary report on the observations in this paper. The radio data are the only means for observing the magnetic fields of the emerging region in the corona, and can thus be used to test models for the structure of emerging magnetic fields. In this case, we do not see any evidence for strong coronal fields during the initial emergence, indicating that the field lines diverge rapidly above the photosphere as expected from simple theory. We follow the emergence of flux over several days and discuss the implications of these observations for theories of flux emergence. Title: Tracking a CME from Cradle to Grave: A Multi-wavelength Analysis of the February 6-7, 1997 Event Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Kosugi, T.; Hudson, H.; Nitta, N.; Thompson, B.; Gurman, J.; Plunkett, S.; Howard, R.; Burkepile, J. Bibcode: 1997SPD....28.0501G Altcode: 1997BAAS...29..908G The partially earth-directed coronal mass ejection (CME) event of 1997 February 6-7 originated from the southwest quadrant of the sun. The CME accelerated from 170 km/s to about 830 km/s when it reached a distance of 25 solar radii. The CME was an arcade eruption followed by bright prominence core structures. The prominence core was tracked continuously from the solar surface to the interplanetary medium by combining data from the Nobeyama radioheliograph (microwaves), Mauna Loa Solar Observatory (He 10830 { Angstroms}), SOHO/EIT (EUV) and SOHO/LASCO (white light). The CME was accompanied by an arcade formation, fully observed by the YOHKOH/SXT (soft X-rays) and SOHO/EIT (EUV). The X-ray and EUV observations suggest that the reconnection proceeded from the northwest end to the southeast end of a filament channel. In the SOHO/EIT images, the the feet of the soft X-ray arcade were observed as EUV ribbons. The CME event also caused a medium sized geomagnetic storm: The hourly equatorial Dst values attained storm level during 18:00-19:00 UT on February 09. This means the disturbance took about 2.25 days to reach the Earth. The first signatures of an IP shock was a pressure jump in the WIND data around 13:00 UT on Feb 09, 1997 which lasted for about 14 hours, followed by flux rope signatures. This CME event confirms a number of ideas about CMEs: The three part structure (frontal bright arcade, dark cavity and prominence core), disappearing filament, elongated arcade formation, and terrestrial effects. We make use of the excellent data coverage from the solar surface to the Earth to address a number of issues regarding the origin and propagation of the geoeffective solar disturbances. We benefited from discussions at the first SOHO-Yohkoh Coordinated Data Analysis Workshop, held March 3-7, 1997, at Goddard Space Flight Center. Title: Currents, Magnetic Fields and Heating in a Solar Active Region Authors: Lee, J.; McClymont, A. N.; Mikic, Z.; White, S. M.; Kundu, M. R. Bibcode: 1997SPD....28.1602L Altcode: 1997BAAS...29R.920L We have compared high-quality microwave images of the radio emission from the corona above an active region with state-of-the-art nonlinear force-free extrapolations of the photospheric magnetic field. The radio images, which are dominated by the opacity provided by the coronal magnetic fields, show excess magnetic field in locations consistent with the expected location of coronal currents. We test the hypothesis that the degree of heating on a given coronal magnetic flux tube is related to the current flowing through it by comparing model radio brightness distributions at different frequencies with the actual observations. In the model we assume that temperature is distributed along the field lines according to quasi-static loop models, and that there is effectively no diffusion across the field lines. This coronal heating model is able to reproduce the radio brightness distributions remarkably well. Title: Multi-wavelength Observations of Transient Microwave Brightenings in a Solar Active Region Authors: Zhang, Jie; Gopalswamy, N.; Kundu, M. R.; Schmahl, E. J.; Lemen, J. R. Bibcode: 1997SPD....28.0163Z Altcode: 1997BAAS...29..891Z We present multi-wavelength Very Large Array observations of two transient microwave brightenings (TMBs) in the solar active region 7135. The events were observed at 2 cm (spatial resolution ~ 2'') and 3.6 cm (spatial resolution ~ 3'') with a temporal resolution of 3.3 s in a time-sharing mode. Soft X-ray data (about 5'' spatial resolution) were available from the Soft X-ray Telescope on board the YOHKOH satellite. The 2 cm and 3.6 cm emission sources were very compact, located near the footpoint of the magnetic loops seen in the X-ray images. The TMBs traced out the three dimensional structure of the magnetic loops where the transient brightenings occurred. For the two events reported in this paper, the projected angular separation between the centroids of 2 and 3.6 cm source is about 2.3'' and 3.1'', respectively. We interpret the spatial and temporal distributions as implying that the 2 and 3.6 cm flux is mainly due to thermal gyro-resonance emmision. The 2 cm emission seems to be at the 3rd gyro-harmonic coming from the 1800 G gyro-resonance layer. The 3.6 cm emission seems to be at both the 2nd and 3rd harmonics, originating from gyro-resonance layers with a magnetic field of 1500 G and 1000 G, respectively. However, the two gyro-resonance layers for 3.6 cm emission are not resolved with the current spatial resolution. The estimated magnetic field gradient near the footpoint of the magnetic loop is about 0.17 G km(-1) and 0.22 G km(-1) for the two events. Title: Microwave Radio Emission from Coronal X-ray Jets Authors: Kundu, M. R.; Shibasaki, K.; Nitta, N. Bibcode: 1997SPD....28.0142K Altcode: 1997BAAS...29..887K We report the first detection of microwave emission from coronal X-ray jets using simultaneously obtained imaging data at 17 GHz (Nobeyama Radioheliograph data) and in X-rays (Yohkoh/SXT data). We present detailed results for one jet on the disk and another at the limb. The 17 GHz emission in the disk event originates from the base (a loop or a system of loops) of the jet, and for the limb jet the microwave emission comes from the base as well as from a part of the X-ray jet. We believe that the collimated jet is optically thin at 17 GHz in most cases. We have investigated more than two dozen jet events and found 17 GHz emission in at least 70% of the cases. The 17 GHz emission is unpolarized. We interpret the microwave emission as thermal, related to the heating of the plasma responsible for the X-ray jet. Title: University of Maryland, Department of Astronomy, College Park, Maryland 20742. Report for the period 1 Oct 1995 - 30 Sep 1996. Authors: Kundu, M. R. Bibcode: 1997BAAS...29..232K Altcode: No abstract at ADS Title: A Multi-Wavelength Analysis of the February 6/7, 1997 Coronal Mass Ejection Authors: Plunkett, S. P.; Gopalswamy, N.; Kundu, M. R.; Howard, R. A.; Thompson, B. J.; Gurman, J. B.; Lepping, R. P.; Hudson, H. S.; Nitta, N.; Hansoka, Y.; Kosugi, T.; Burkepile, J. T. Bibcode: 1997ESASP.404..615P Altcode: 1997cswn.conf..615P No abstract at ADS Title: Radio Observations of Coronal X-ray Jets Authors: Kundu, Mukul R. Bibcode: 1997IAUJD..19E...5K Altcode: Among many discoveries, the Yohkoh/SXT experiment has discovered X-ray jets which are transitory X-ray enhancements with well-collimated motion (Shibata et al. 1992, PASJ,161,L173). In many cases, the jets are associated with small flares at or near their foot points and the motion appears to be a real flow of plasma at temperatures of a few million degrees. We have detected microwave radio emission at 17 GHz from these coronal jets, which appears to be thermal in nature. The microwave emission appears to be associated mainly with the base of the jets although in some cases the jets (which may be optically thin at 17 GHz) produce microwave emission. We have found evidence of non-thermal radio emission from jets in the form of metric type III bursts. The type III bursts are spatially and temporally coincident with the X-ray jets.The implications of both sets of observations will be discussed. Title: Radio and X-Ray Studies of a Coronal Mass Ejection Associated with a Very Slow Prominence Eruption Authors: Gopalswamy, N.; Hanaoka, Y.; Kundu, M. R.; Enome, S.; Lemen, J. R.; Akioka, M.; Lara, A. Bibcode: 1997ApJ...475..348G Altcode: We report on the observations of an X-ray coronal mass ejection (CME) with its three part structure: frontal loop, coronal cavity, and the eruptive prominence core. The prominence core was observed in microwaves, and the frontal loop was observed in X-rays. A coronal volume much larger than that occupied by the prominence seems to be affected by the eruption. Formation of an arcade structure was also observed beneath the erupting prominence. X-ray enhancement at the arcade persisted for several hours similar to long decay events. At the apex of the arcade there was a bright knot, which we interpret as the reconnection region from which the filament gets detached. We determined the trajectories of the frontal loop and the prominence core and found them to have very different characteristics. The CME showed an extremely small acceleration, while the prominence had a linear motion in the beginning followed by an exponential rise. However, during the several hours of simultaneous observation, the prominence did not catch up with the frontal loop. We determined the evolution of the CME mass, which increased by a factor of 4 during our observations. We discuss the implications of the observations in the general context of coronal mass ejections. Title: A Giant Prominence Eruption Observed by Nobeyama Radioheliograph and YOHKOH Spacecraft Authors: Gopalswamy, N.; Hanaoka, Y.; Kundu, M. R.; Shibasaki, K.; Koshiishi, H.; Enome, S.; Lemen, J. R. Bibcode: 1997IAUJD..19E...4G Altcode: The results of an investigation of a giant prominence which erupted from the northwest limb of the Sun on 1994 April 05, will be reported. The event could be traced back to a large prominence of March 19, 1994 above the east limb. The filament was located in the north-south direction when it appeared on the disk. At about 23:00 UT on April 05, the filament started slowly rising and then accelerated. The speed of the prominence was was only 75 km s^{-1} when it reached a height of about 0.5 R_ odot above the surface. Preliminary examination shows that the eruption caused a geomagnetic storm on April 07 at 20:00 UT. We study the dynamical and physical properties of the erupting prominence and obtain physical parameters of the prominence plasma. In X-rays, the region of eruption was relatively faint. After the eruption, however, there was a large void at the previous location of the prominence and an arcade formed progressively spreading from south to north along the limb. Based on the X-ray and radio observations, we determine the characteristics of the pre- and post-eruption structures. Title: Radio Continuum and Type III Bursts Associated with Coronal X-Ray Structures Authors: Raulin, J. P.; Kundu, M. R.; Nitta, N.; Raoult, A. Bibcode: 1996ApJ...472..874R Altcode: In this paper, we report the detection of a metric continuum burst source at the top of a coronal loop observed in soft X-rays. The continuum burst was probably a flare continuum that lasted more than 1 hr. This is the first observation of such metric continuum emission produced by energetic electrons with high-spatial resolution imaging instruments in both X-rays and radio. The nonthermal radio emission appears to be associated with the rupture of a part of the loop top and the ejection of soft X-ray plasma at the top of the coronal loop. We have also identified X-ray coronal structures in which type III emitting electron beams propagate. The metric continuum is most likely caused by second-harmonic plasma emission, and the electron density in the soft X-ray structure where type Ills are observed is close to the critical plasma density derived from radio observations. Title: Radio and X-ray Imaging Observations of Solar Flares and Coronal Transients Authors: Kundu, M. R. Bibcode: 1996SoPh..169..389K Altcode: We present a review of selected studies based upon simultaneous radio and X-ray observations of solar flares and coronal transients. We use primarily the observations made with large radio imaging instruments (VLA, BIMA, Nobeyama, and Nançay) along with Yohkoh/SXT and HXT and CGRO experiments. We review the recent work on millimeter imaging of solar flares, microwave and hard X-ray observations of footpoint emission from flaring loops, metric type IV continuum bursts, and coronal X-ray structures. We discuss the recent studies on thermal and nonthermal processes in coronal transients such as XBP flares, coronal X-ray jets, and active region transient brightenings. Title: Observation and model calculations of sunspot ring structure at 8.46GHz Authors: Gopalswarmy, N.; Raulin, J. P.; Kundu, M. R.; Hildebrandt, J.; Krueger, A.; Hofmann, A. Bibcode: 1996A&A...316L..25G Altcode: We present Very Large Array (VLA) observations of AR 7542 which demonstrate the existence of definite ring and horse-shoe structures of a sunspot in intensity (I) and polarization (V) at 8.46GHz (3.5cm wavelength) and compare them with model calculations of gyroresonance radiation. The VLA measurements have been made on three different days in July 1993 when AR 7542 was at three different longitudes which allows us to study the effect of viewing angle on sunspot-associated microwave emission. Model calculations of gyroresonance radiation have been carried out using a modified dipole model corresponding to the observed photospheric magnetic field strength and average temperature/electron density distributions consistent with soft X-ray and EUV observations (for the lower atmosphere) as well as theoretical assumptions (for the corona). The calculated I and V maps were found to be generally consistent with the radio observations. We obtain information on the magnetic scale length in vertical and horizontal directions above the sunspot and about the distribution of other plasma parameters (temperature, density) inside the radio source region. Title: Yohkoh/SXT observations of a coronal mass ejection near the solar surface Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen, J. R.; Akioka, M. Bibcode: 1996NewA....1..207G Altcode: We report the observations of a coronal mass ejection (CME) using the Soft X-ray Telescope on board the Yohkoh Mission. The CME had the familiar three part structure (frontal loop, prominence core and a cavity). The erupting prominence was observed by the Nobeyama radioheliograph. We were able to determine the mass of the CME (2.6 × 1014 g) from X-ray observations which seems to be at the lower end of the range of CME masses reported before from white light observations. This is the first time the mass of a CME has been determined from X-ray observations. The height of onset of the CME was 0.3R⊙. The CME moved much faster than the erupting prominence while its acceleration was smaller than that of the erupting prominence. J. Leonard Culhane Title: Comprehensive Multiwavelength Observations of the 1992 January 7 Solar Flare Authors: Silva, Adriana V. R.; White, Stephen M.; Lin, Robert P.; de Pater, Imke; Gary, Dale E.; McTiernan, James M.; Hudson, Hugh S.; Doyle, J. Gerry; Hagyard, Mona J.; Kundu, Mukul R. Bibcode: 1996ApJS..106..621S Altcode: Observations of a solar flare that occurred at 2022 UT on 1992 January 7, during the 1991 December/1992 January Max `91 campaign, are presented. This flare was observed simultaneously in Hα, radio (at microwave and millimeter wavelengths), and soft and hard X-rays (by the Yohkoh spacecraft) with high spatial and moderate spectral resolution. A comparison of magneto grams before and after the flare shows evidence of the emergence of new magnetic flux of opposite polarity at the flare site. Although this flare was only of moderate size (GOES classification C8.9 and Hα importance SF), it exhibited several distinct bursts and at least 10 spatially distinct hard/soft X-ray sources. Cospatial Hα brightenings suggest that most of the X-ray sources are located at footpoints of magnetic loops. Two of the hard X-ray sources have no Hα counterparts and are therefore believed to be located at loop tops. The flare consisted of three bursts of particle acceleration followed by a purely thermal phase. High spectral resolution Ca XIX line profiles indicate upflows shortly after the second acceleration phase. Analysis of the microwave/hard X-ray/soft X-ray emission from individual sources provides information on the radio emission mechanisms, the energetic electron population, the magnetic field strength, and the plasma density. These parameters were estimated for the two microwave sources observed during the third acceleration burst; these sources were simultaneously detected in soft X-rays, and one of the sources is also seen in hard X-ray maps. Although the microwave emission is consistent with the gyro synchrotron mechanism, the millimeter emission, which peaks during the thermal phase when all nonthermal activity has ceased, is likely due to thermal bremsstrahlung from the soft X-ray emitting hot plasma. The energy lost to collisions by the energetic (>15 keV) electrons and the energy contained in the thermal plasma are calculated for each source. The energy injected by the nonthermal electrons from all sources is estimated to be 1030 ergs. Only the soft X-ray sources with gradual time profiles seem to show the Neupert effect. Title: A Model for Active Region Emission at Centimeter Wavelengths Authors: Nindos, A.; Alissandrakis, C. E.; Gelfreikh, G. B.; Kundu, M. R.; Dere, K. P.; Korzhavin, A. N.; Bogod, V. M. Bibcode: 1996SoPh..166...55N Altcode: We present multi-frequency observations and model computations of the microwave emission of a solar active region. The radio observations were obtained with the RATAN-600 at several wavelengths between 0.8 and 31.6 cm and with the VLA at 6 and 20 cm. The active region was also observed in the EUV O Iv lines by the HRTS instrument aboard the Space Shuttle Spacelab-2 mission. These lines are formed in the chromosphere-corona transition region and their intensity ratio is sensitive to pressure. Photospheric magnetograms provided both the longitudinal and the transverse component of the magnetic field. The microwave observations were checked against model computations taking into account both the free-free and the gyro-resonance emission mechanisms and using the pressure data from the O IV lines. The magnetic field was computed through constant-α force-free extrapolations of the longitudinal photospheric field. We computed both the flux from 2 to 20 cm and the spatial structure of the microwave emission at 6 and 20 cm. The comparison of the computed and observed flux spectra allowed us to estimate the magnetic field strength at the base of the transition region and in the low corona, as well as the values of the conductive flux and the height of the base of the transition region. The model maps at 6 cm and 20 cm showed that α was not constant above the active region; the same conclusion was reached on the basis of the photospheric observations. The use of pressure measurements allowed us to identify microwave structures which were determined by pressure enhancements. At 6 cm the computations confirmed the fact that the magnetic field is the principal factor that determines the structure of sunspot-associated sources and showed that the effect of pressure variations was small. Pressure variations were more important at 20 cm, where the peak of the emission was associated with the sunspot and a diffuse component was associated with the plage which had an average pressure higher by a factor of 1.54 than the sunspot. Title: Radio and X-ray manifestations of a bright point flare Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen, J. R. Bibcode: 1996AIPC..374..408G Altcode: 1996hesp.conf..408G We have found remarkably different manifestations of a bright point flare in X-ray and radio (microwave) wavelengths, unlike previous observations. In X-rays, the BP flare was relatively simple while in radio, the bright point flare had a large scale component and a transient moving component. The large scale structure may be the radio counterpart of large scale structures sometimes seen during X-ray BP flares. The transient component was also compact and moved away from the location of the X-ray BP flare with a speed of ∼60 km s-1. The compact source also showed fast time structure which suggests nonthermal emission mechanism for the transient sources. Title: Nonthermal radio emission from coronal X-ray structures Authors: Kundu, Mukul R.; Raulin, Jean-Pierre; Nitta, Nariaki Bibcode: 1996AIPC..374..402K Altcode: 1996hesp.conf..402K We have provided evidence that certain coronal X-ray structures such as flaring X-ray bright points and X-ray jets give rise to nonthermal radio emission in the form of metric type III bursts. We have shown an example of a metric type IV/flare continuum being associated with the rupture of a flaring loop-top and the ejection of X-ray emitting material. Title: Tracking Type III and Type II Solar Radio Bursts from Metric to Hectometric Wavelengths using Ground-based and Space-borne Observations Authors: Gopalswamy, N.; Kundu, M. R.; Kaiser, M. L.; Kahler, S. W.; Kondo, T.; Isobe, T.; Akioka, M. Bibcode: 1996AAS...188.1908G Altcode: 1996BAAS...28..851G There exists a controversy regarding the origin of coronal and interplanetary (IP) shocks. Present observations shows that coronal shocks are associated with flares while the IP shocks are associated with coronal mass ejections (CMEs). An important question in this connection is whether the IP shocks are extensions of the coronal shocks or they are independently driven by CMEs. The coronal shocks have traditionally been inferred from metric type II radio bursts. The ionospheric cut-off around 20 MHz had been a hurdle in arriving at a firm conclusion regarding the continuation of type II bursts to frequencies lower than the ionospheric cut off. The WAVES experiment on board the WIND spacecraft has essentially removed this hurdle so that we are able to track metric radio bursts to hectometric wavelengths. We have identified about two dozen type II bursts observed by the Hiraiso Radio Spectrograph (HiRAS) after the launch of the WIND satellite. Most of these type II bursts were accompanied by type III bursts. We have positively identified the solar flares associated with all the events. When we examined the WIND Radio and Plasma waves (WAVES) data, we found the following: (i) Most of the metric (Hiraiso) type III bursts have counterparts in the WAVES data; (ii) None of the metric type II bursts have counterparts in the WAVES data. This result suggest that coronal shocks responsible for metric type II bursts are blast waves which decay rapidly within the inner corona while the electron beams producing type III bursts continue to propagate to the IP medium. Title: Millimeter Observations of a B5.6 Flare Authors: Raulin, J. -P.; White, S. M.; Kundu, M. R.; Silva, A. V. R.; Shibasaki, K. Bibcode: 1996AAS...188.4503R Altcode: 1996BAAS...28..894R We present millimeter imaging observations of a B5.6 flare which occured on 1994 August 16 in the active region AR 7765. The BIMA interferometer and the Nobeyama radioheliograph observed both the impulsive phase and the thermal phase of the flare emission. The 3.5 mm maps obtained with BIMA allowed us to determine the location of the radio source and its properties at different phases of the flare evolution. In X-ray wavelengths the impulsive phase was detected by the first two channels of BATSE (25-50 keV, 50-100 keV); although YOHKOH/SXT did not observe the impulsive phase, it was possible to image the post-flare loop in soft X-rays. We compare the images of the flare at different wavelengths and discuss the relevance of millimeter emission in the context of flare models. Title: Large Scale Features of the Radio Sun Authors: White, S. M.; Gary, D. E.; Kundu, M. R. Bibcode: 1996AAS...188.7907W Altcode: 1996BAAS...28Q.956W We present full-disk images of the Sun at 5 GHz made by observing 26 different fields with the Very Large Array and combining them using mosaicking techniques. The resulting image combines sensitivity to large-scale structures with good resolution. Full-disk images at 0.33, 1.4 and 17 GHz, a high-resolution magnetogram and a soft X-ray image are compared with the 5 GHz image to investigate the physical properties of large-scale features. Title: Coronal X-Ray Structures and Metric Radio Type III and IV Bursts Authors: Kundu, M. R.; Raulin, J. -P.; Nitta, N.; Raoult, A. Bibcode: 1996AAS...188.8609K Altcode: 1996BAAS...28R.964K Over the past several years Yohkoh/SXT experiments have led to the discovery of many new and interesting dynamic phenomena. Of particular interest are the flaring X-ray bright points (XBPs), X-ray jets, and flare associated plasmoids and other ejecta. We have looked for evidence of nonthermal processes occurring in these X-ray events, using radio bursts of spectral types III and IV. We have used positional information of metric radio bursts using the Nancay (France) Radioheliograph in the frequency range 150-450 MHz simultaneously with the Yohkoh experiments. We have evidence of nonthermal type III burst emission in the meter wave range in association with flaring XBPs and certain classes of X-ray jets. We have detected metric structures, namely flaring loops (possibly plasmoids) and other ejecta. The implications of these findings will be discussed in terms of our understanding of radio bursts of different spectral types. Title: Polarization of Microwaves Emitted From A Bipolar Active Region Authors: Lee, Jeongwoo; White, Stephen; Gopalswamy, N.; Kundu, M. R. Bibcode: 1996AAS...188.3603L Altcode: 1996BAAS...28R.873L High resolution microwave maps of a complex bipolar active region, AR6615, were obtained using the VLA on 1991 May 7 at three frequencies, 4.9 GHz, 8.4 GHz, and 15 GHz. Comparison of this microwave observation with Big Bear magnetogram suggests that inversion and depolarization of microwave emission must have occurred at different sites of the active region depending on frequency. For quantitative interpretation of the polarization data, we constructed the coronal magnetic fields above the active region using the potential field extrapolation. In the model, we identified the quasi-transverse (QT) surface across which change of the polarization may occur. It is found that the required topology of the QT surface to explain the observed polarization is correctly predicted by the potential field model, although the locations of the 15 GHz gyroresonance sources required a nonlinear force-free field extrapolation in part. With the calculation of the mode coupling coefficient along the QT surface, we were able to locate the region of depolarization above a strong sunspot, consistent with the observation. We also discuss the appropriate theoretical gyroresonant opacity for waves propagating perpendicular to the magnetic fields, as needed to understand the observed polarization across the magnetic neutral line. Applicability of the present results to study of the coronal magnetic structure above complex bipolar regions, in general, is briefly discussed. Title: A Multi Wavelength Study of Active Region Development Authors: Lara, A.; Gopalswamy, N.; Kundu, M. R.; Perez-Enriquez, R.; Koshiishi, H.; Enome, S. Bibcode: 1996AAS...188.3601L Altcode: 1996BAAS...28Q.873L We report on a study of the evolution of several active regions during 1993 April 17-28 using data obtained at multiple wavelengths that probe various heights of the active region corona. We use simultaneous microwave (1.5 and 17 GHz) and Soft X-ray images obtained by the Very Large Array (VLA), the Nobeyama Radio Heliograph (NRH) and the Soft X-ray Telescope (SXT) on board the Yohkoh spacecraft. We also use photospheric magnetograms from Kitt Peak National Observatory to study the development of Solar Active Regions. We have followed the development of various observed parameters such as brightness temperature and polarization using radio images. The X-ray data were used to track the development of density and temperature of active regions. Using the fact that the quiet active region radiation is thermal and adopting proper emission mechanism at each frequency domain, we construct a consistent picture for the three dimensional structure of the active regions. Particular attention has been paid to the mode coupling observed at 17 GHz while the active regions crossed the solar disk. Title: A model of the atmosphere above a sunspot from radio observations Authors: Zlotnik, E. Ya.; Kundu, M. R.; White, S. M. Bibcode: 1996R&QE...39..255Z Altcode: The results of VLA observations of an unusual source of microwave radiation, associated with the sunspot NOAA 7789 on October, 15, 1994, are presented. The fine structure of the source, which is a ring structure in intensity and polarization at frequencies 4.5 and 8.0 GHz, is discussed. It is shown that the features observed can be explained by a thermal cyclotron mechanism if the magnetic field is approximated by a vertical dipole buried under the photosphere, but the spatial distributions of kinetic temperature and electron density in the atmosphere above the sunspot differ considerably from the standard model. A two-dimensional source model (the dependences of the parameters on the height and distance from the center of the sunspot), which fits the observations at the above frequencies, is evolved. The principal physical result is that the data observed are explainable by the presence of an unexpectedly dense cool plasma in the atmosphere over the center of the umbra. Title: Coronal Transients in Radio and X-rays Authors: Kundu, Mukul R. Bibcode: 1996Ap&SS.243...15K Altcode: 1996IAUCo.154...15K We present a summary of several studies of transient coronal phenomena based upon high spatial resolution radio imaging data along with Yohkoh SXT and HXT observations. In addition to normal flares the studies also involve such exotic events as active region transient brightenings (ARTB) and coronal jets and bright points. We provide evidence of nonthermal processes in flaring X-ray bright points from spatially resolved meter-wave data, existence and propagation of type II burst emitting electrons in coronal jets, radio signatures of ARTB's, and beaming of electrons producing microwave and hard X-rays. The implications of these observations are discussed. Title: Metric Type III bursts associated with soft X-ray jets. Authors: Raulin, J. P.; Kundu, M. R.; Hudson, H. S.; Nitta, N.; Raoult, A. Bibcode: 1996A&A...306..299R Altcode: From soft X-ray and metric radio observations with high temporal and spatial resolution, we show that electron acceleration in the form of Type III bursts occurs in association with coronal jets observed by the Yohkoh soft X-ray telescope. The excellent correspondence between the positions of the radio sources observed at different frequencies and the X-ray jets strongly suggests that electron beams propagate along the relatively dense paths formed by the jets. Assuming a constant temperature for the jets, one can estimate the electron density from the soft X-ray measurements. These computed electron densities agree well with the values derived from Type III bursts produced by the plasma emission process. The observations are consistent with the idea that strong particle acceleration accompanies magnetic reconnection in these events as well as in solar flares. Title: Detection of Large-Scale Radio Structure and Plasma Flow during a Solar Bright Point Flare Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen, J. R. Bibcode: 1996ApJ...457L.117G Altcode: We report on the detection of a large-scale radio structure and plasma flow associated with a bright point flare observed on 1993 July 11. The bright point (BP) flare was simultaneously imaged by the Nobeyama radioheliograph at 17 GHz and the Soft X-Ray Telescope on board the Yohkoh mission. The microwave emission consists of a large-scale structure and a compact moving source. The large-scale component seems to be the radio counterpart of large-scale loop structures sometimes observed in association with BP flares in X-rays. The compact source moved from the location of the X-ray BP flare with a speed of about 60 km s-1, which suggests a plasma flow. Spatial comparison between X-ray and radio data shows that the BP flare had different manifestations in the two wavelength domains. The emission peaks in the two wavelength domains did not coincide, which suggests cool plasma flow along the large-scale radio structure. We were able to determine the temperature and emission measure of the BP flare plasma from the X-ray data, and thus we computed the expected radio flux from the X-ray--emitting plasma. We found that the computed radio flux was much smaller than the total observed radio flux. Title: First Images of a Solar Flare at Millimeter Wavelengths Authors: Silva, Adriana V. R.; White, Stephen M.; Lin, Robert P.; de Pater, Imke; Shibasaki, K.; Hudson, Hugh S.; Kundu, Mukul R. Bibcode: 1996ApJ...458L..49S Altcode: We present the first high spatial resolution images of a solar flare at millimeter wavelengths. On 1994 August 17, a GOES soft X-ray class M1 flare was observed by the Berkeley-Illinois-Maryland Array at 86 GHz by the Nobeyama 17 GHz array and by the Yohkoh spacecraft. The flare displayed both a prominent impulsive phase in microwaves and a gradual phase that lasted over 30 minutes. The millimeter data were taken only during the gradual phase. The millimeter images show a source with a size of ~8", a peak brightness temperature of ~106 K, and maximum optical depth of 0.09. At both X-ray and radio wavelengths, the emitting region appeared to be compact (<~20"). In soft X-ray, the images are resolved into two sources: one located at a footpoint and the other at the top of the flaring loop. The millimeter emission is consistent with the predicted free-free flux from an isothermal temperature (~14 MK) loop-top source, a multitemperature footpoint source with a hot (~22 MK), and a cold (~12 MK) component. Most (80%) of the millimeter flux density originates from the top of the magnetic loop, and the footpoint contribution is only 20%. Title: VLA Observations of a Solar Active Region at 6.2 and 3.5 CM Wavelength Compared with Model Calculations Authors: Hildebrandt, J.; Kruger, A.; Gopalswamy, N.; Raulin, J. -P.; Kundu, M. R. Bibcode: 1996ASPC...93..369H Altcode: 1996ress.conf..369H No abstract at ADS Title: Three Part Structure of a CME Revealed by X-Ray and Microwave Observations Authors: Gopalswamy, N.; Kundu, M. R.; Lara, A.; Hanaoka, Y.; Enome, S.; Lemen, J. R.; Akioka, M. Bibcode: 1996ASPC..111..393G Altcode: 1997ASPC..111..393G The authors present X-ray (Yohkoh/SXT) and microwave (17 GHz Nobeyama) observations of the 1993 July 10 - 11 CME. During this event, all the substructures of a classical CME are revealed: frontal loop in X-rays, prominence core in microwaves, dark cavity between prominence and frontal loop in X-rays, and arcade structure beneath the prominence in X-rays. Title: The Radio Outburst of eta Carinae Authors: White, S. M.; Duncan, R. A.; Lim, J.; Drake, S. A.; Kundu, M. R. Bibcode: 1996ASPC...93...59W Altcode: 1996ress.conf...59W No abstract at ADS Title: Nonthermal Radio Emission from Coronal X-ray Jets Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.; Hudson, H. S.; Raoult, A. Bibcode: 1996ASPC...93..375K Altcode: 1996ress.conf..375K No abstract at ADS Title: Detection of Nonthermal Radio Emission from Coronal X-ray Jets Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.; Hudson, H. S.; Raoult, A.; Shibata, K.; Shimojo, M. Bibcode: 1996mpsa.conf..445K Altcode: 1996IAUCo.153..445K No abstract at ADS Title: A Search for Rotational Modulation in the EUV Emission from AB Doradus Authors: White, S. M.; Lim, J.; Rucinski, S. M.; Roberts, C.; Kilkenny, D.; Ryan, S. G.; Prado, P.; Kundu, M. R. Bibcode: 1996aeu..conf..165W Altcode: 1996IAUCo.152..165W No abstract at ADS Title: First Images of a Solar Flare at Millimeter Wavelengths Authors: Silva, Adriana V. R.; White, Stephen M.; Lin, Robert P.; de Pater, Imke; Shibasaku, K.; Hudson, Hugh S.; Kundu, Mukul R. Bibcode: 1996ADIL...AS...01S Altcode: We present the first high-spatial-resolution images of a solar flare at millimeter wavelengths. On 1994 August 17, a GOES soft X--ray class M1 flare was observed by the Berkeley--Illinois--Maryland Array (BIMA) at 86 GHz, by the Nobeyama 17 GHz array, and by the Yohkoh spacecraft. The flare displayed both a prominent impulsive phase in microwaves and a gradual phase which lasted over 30 minutes. The millimeter data were taken only during the gradual phase. The millimeter images show a source with a size of $\sim$8\arcsec, a peak brightness temperature of ~ 10^6 K, and maximum optical depth of 0.09. At both X--ray and radio wavelengths the emitting region appeared to be compact (< 20 arcseconds). In soft X--ray the images are resolved into two sources: one located at a footpoint and the other at the top of the flaring loop. The millimeter emission is consistent with the predicted free-free flux from an isothermal temperature (~ 14 MK) looptop source and a multi--temperature footpoint source with a hot (~ 22 MK) and a cold (~ 12 MK) component. Most (80%) of the millimeter flux density originates from the top of the magnetic loop, and the footpoint contribution is only 20%. Title: VLA and YOHKOH Observations of an M1.5 Flare Authors: Gopalswamy, N.; Raulin, J. -P.; Kundu, M. R.; Nitta, N.; Lemen, J. R.; Herrmann, R.; Zarro, D.; Kosugi, T. Bibcode: 1995ApJ...455..715G Altcode: A major solar flare (X-ray importance M1.5 and optical importance SB) was fully observed by the Very Large Array and the Yohkoh mission on 1993 April 22. Both thermal and nonthermal emissions were observed in radio. In soft X-rays, the flare was confined to a compact region in an arcade. In hard X-rays, there were two prominent footpoints, coincident in projection with the soft X-ray footpoints and located on either side of the magnetic neutral line inferred from photospheric magnetograms The Yohkoh Bent Crystal Spectrometer (B CS) data provided important context information which was helpful in cross-checking the quantitative agreement between the radio and X-ray data. The microwave spectrum peaked around 10 GHz and showed Razin suppression in the beginning. Later on, the low-frequency spectral index dropped to a value of 2, suggesting thermal emission. The VLA images of the flare at 1.5 GHz show that the flare emission started as a single source above one footpoint; later on, the emission centroid moved toward the soft X-ray structure to finally become cospatial with the latter. The two locations of the 20 cm source corresponded to nonthermal (footpoint source) and thermal (source cospatial with the soft X-ray structure) emissions. We performed temperature and emission measure analysis of the X-ray data (SXT, BCS, and HXT) and used them as input to determine the expected radio emission. While there is morphological agreement between the radio and soft X-ray structures in the thermal phase, the 20 cm brightness temperature shows quantitative agreement with temperature derived from the BCS data. We were able to identify three emission mechanisms contributing to the 20 cm radio emission at different times without any ad hoc assumption regarding emission mechanisms. Razin-suppressed nonthermal gyroresonance emission, plasma emission, and thermal free-free emission seem to be operating and are found to be consistent with the plasma parameters derived from the X-ray data. The magnetic field structure in the flaring region showed differences before and after the flare as traced b soft X-ray structures in the flaring region and confirmed by 20 cm radio images. The superhot component with a temperature of 32 MK was observed in hard X-ray images and in light curves during the impulsive phase of the flare with possible radio signatures at 20 cm wavelength. We derived the physical parameters of the flaring plasma, the magnetic field, and the characteristics of nonthermal particles in the flaring region. Title: Microwave and Hard X-Ray Observations of Footpoint Emission from Solar Flares Authors: Kundu, M. R.; Nitta, N.; White, S. M.; Shibasaki, K.; Enome, S.; Sakao, T.; Kosugi, T.; Sakurai, T. Bibcode: 1995ApJ...454..522K Altcode: We investigate radio and X-ray imaging data for two solar flares in order to test the idea that asymmetric precipitation of nonthermal electrons at the two ends of a magnetic loop is consistent with the magnetic mirroring explanation. The events we present were observed in 1993 May by the HXT and SXT X-ray telescopes on the Yohkoh spacecraft and by the Nobeyama 17 GHz radioheliograph. The hard X-ray images in one case show two well-separated sources; the radio images indicate circularly polarized, nonthermal radio emission with opposite polarities from these two sources, indicating oppositely directed fields and consistent with a single-loop model. In the second event there are several sources in the HXT images which appear to be connected by soft X-ray loops. The strongest hard X-ray source has unpolarized radio emission, whereas the strongest radio emission lies over strong magnetic fields and is polarized. In both events the strongest radio emission is highly polarized and not coincident with the strongest hard X-ray emission. This is consistent with asymmetric loops in which the bulk of the precipitation (and hence the X-ray emission) occurs at the weaker field footpoint. Title: Microwave proxies for sunspot blocking and total irradiance Authors: Schmahl, E. J.; Kundu, M. R. Bibcode: 1995JGR...10019851S Altcode: The microwave flux of the Sun is responsive to the same conditions that produce magnetically structured radiation at visible and X ray wavelengths, and so the solar flux at high radio frequencies such as 2800 MHz (10.7 cm) has been used as a proxy for solar optical variations. We have previously found that the microwave flux time series show spectral variations that provide useful proxy information for total irradiance, and we have extended our analysis of the daily solar fluxes from Toyokawa Observatory at 1000, 2000, 3750, and 9400 MHz, in addition to the Ottawa 2800-MHz flux, for the years 1980-1989. An essential ingredient in our analysis is the extraction of the rotationally-modulated microwave component, which differs from the ``S component'' as recently defined in the literature. The rotationally-modulated fraction of the emission contains a significant, often dominant, contribution from gyroresonance emission, whereas the S component, as defined by the excess above the cycle minimum level, usually does not.

This allows us to distinguish plage-associated emission from spot-associated emission in the time series of microwave flux. We show that in combination, the microwave fluxes for 1000-9400 MHz, which span the spectral peak of spot-associated emission, provide a very good proxy both the active cavity radiometer irradiance monitor (ACRIM) total irradiance and the sunspot-blocked component of the irradiance, even without optical sunspot observations. Over the 1984-1989 period, this proxy has a weighted correlation with ACRIM of 95%, and an RMS deviation from the total irradiance of 0.27 w/m2, slightly better than the deviation (0.35 w/m2) found using optical data. Title: The Radio Properties of Solar Active Region Soft X-Ray Transient Brightenings Authors: White, S. M.; Kundu, M. R.; Shimizu, T.; Shibasaki, K.; Enome, S. Bibcode: 1995ApJ...450..435W Altcode: We present the results of a search for radio emission from active-region transient brightenings identified in Yohkoh soft X-ray telescope observations of active region AR 7260. We present detailed observations of four events in which 17 GHz radio emission is clearly detected in observations by the Nobeyama radioheliograph. The time profiles of the 17 GHz data are very similar to those of the soft X-ray fluxes, and the 17 GHz flux is very close to that expected from plasma with the temperature and emission measure derived for the soft X-ray emitting material from filter ratios. No impulsive nonthermal radio emission was detected from any of the four events, although each was at least GOES class B 1 in soft X-rays. Weak hard X-rays may have been detected by GRO/BATSE from the strongest of the events, but not from two others. These negative results leave open the possibility that there is a difference between active region transient brightenings and solar flares, in that the former do not convert a significant amount of the released energy into accelerated electrons. However, confirmation of this hypothesis will require a larger sample of events. Title: Detection of Nonthermal Radio Emission from Coronal X-Ray Jets Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.; Hudson, H. S.; Shimojo, M.; Shibata, K.; Raoult, A. Bibcode: 1995ApJ...447L.135K Altcode: We report the detection of a type III burst in association with a dynamic X-ray coronal jet observed by Yohkoh/SXT. The type III burst observed with the Nancay (France) multifrequency radioheliograph is spatially and temporally coincident with the X-ray jet. The radio locations at different frequencies (236.6 and 164 MHz) are aligned along the length of the jet. The observation of the type III burst in association with the X-ray jet implies the acceleration of electrons to several tens of keV, along with the heating responsible for the production of soft X-rays. This association implies the existence of open field lines in dense coronal structures identified on the Sun's disk. This is the first observation of dense coronal structures on the disk, along which type III emitting nonthermal electrons propagate. We find that this structure begins to form before the type III emission. At the time of the type III burst we estimate a density of 6--10 x 108 cm-3 for a temperature of ~5--6 MK at an altitude of 20,000 km. Title: Observations of Continuum and - Emission from Eta Carinae at a Wavelength of 3 CM Authors: Duncan, R. A.; White, S. M.; Lim, J.; Nelson, G. J.; Drake, S. A.; Kundu, M. R. Bibcode: 1995RMxAC...2...23D Altcode: No abstract at ADS Title: Metric Type III Bursts from a Flaring X-Ray Bright Point near an Active Region Authors: Kundu, M. R.; Raulin, J. P.; Pick, M.; Strong, K. T. Bibcode: 1995ApJ...444..922K Altcode: X-ray bright points (XBPs) are known to show variability on a number of timescales, including impulsive X-ray brightenings. The relationship between these XBP 'flares' and normal flares is poorly known. A fundamental question is whether nonthermal acceleration of particles takes place in XBP flares. We address this issue by seravhing for nonthermal radio emission at metric wavelengths from flaring XBPs identified in Yohkoh/SXT data. Unequivocal evidence for type III-like radio bursts usually attributed to beams of nonthermal electrons on open field lines was found recently by Kundu et al. This suggests that XBP flares are similar to normal flares and can indeed accelerate nonthermal populations of energetic particles. Here we provide further evidence of metric type III bursts from flaring XBPs located near active regions. Title: The Magnetic Field Over an Isolated Symmetric Sunspot Authors: White, S. M.; Kundu, M. R.; Zlotnik, E. Ya.; Zheleznyakov, V. V.; Nitta, N. Bibcode: 1995SPD....26..718W Altcode: 1995BAAS...27..970W No abstract at ADS Title: Intense Radio Outburst from the Supermassive Star eta Carinae Authors: Duncan, R. A.; White, S. M.; Lim, J.; Nelson, G. J.; Drake, S. A.; Kundu, M. R. Bibcode: 1995ApJ...441L..73D Altcode: On five occasions between 1992 June 29 and 1994 May 3, we have used the Australia Telescope Compact Array (ATCA) to image Eta Carinae at a wavelength of 3 cm and a resolution of 1 arcsec. These observations have revealed remarkable activity. Since 1992 June, the total flux density has increase from 0.8 to 2.2 Jy, and the original single compact source has grown to a complex of sources spread over an area of about 16 sq arcsec. Strong hydrogen recombination-line spectral emission has appeared at the site of the strongest of these new sources. This recombination emission has the largest spectral width ever observed from a star, +/- 250 km/s, and reveals gas with turbulent velocities as great as 250 km/s approaching us at an average velocity of about 200 km/s. We believe that this radio outburst has been caused by a more than threefold increase of ultraviolet luminosity, and consequent ionization of previously neutral gas clouds. Title: Radio Counterpart of an X-ray Bright Point Flare Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.; Lemen, J. R. Bibcode: 1995SPD....26.1317G Altcode: 1995BAAS...27Q.991G No abstract at ADS Title: Spatially resolved Millimeter (86 GHz), Microwave (17 GHz) and X-Ray Observations of the 17 August 94 flare Authors: Silva, A. V. R.; Lin, R. P.; de Pater, I.; White, S. M.; Kundu, M. R. Bibcode: 1995SPD....26..804S Altcode: 1995BAAS...27..972S No abstract at ADS Title: Nouthermal Radio Emission From Coronal X-Ray Jets Authors: Raulin, J. P.; Kundu, M. R.; Hudson, H. S.; Nitta, N.; Raoult, A. Bibcode: 1995SPD....26.1318R Altcode: 1995BAAS...27..991R No abstract at ADS Title: Book Review: Solar Magnetic Fields Authors: Kundu, Mukul R.; Schüssler, M.; Schmidt, W. Bibcode: 1995ComAp..18...36K Altcode: No abstract at ADS Title: Characteristics of Two Simple Microwave Bursts Authors: Kundu, M. R.; White, S. M.; Nitta, N.; Shibasaki, K.; Enome, S. Bibcode: 1995LNP...444...75K Altcode: 1995cmer.conf...75K We present simultaneous microwave and X-ray data for two microwave bursts with simple impulsive time profiles. The 17 GHz images show compact sources, and in the one case for which we have simultaneous soft and hard X-ray images, they also show compact sources coincident with the radio source. One of the bursts is barely detected in soft X-rays, yet has a moderate 17 GHz flux,. Title: Surprises in the Radio Signatures of CMEs Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1995LNP...444..223G Altcode: 1995cmer.conf..223G We discuss several results regarding the relationship between coronal mass ejections (CMEs) and metric radio emissions which have changed our understanding of these phenomena considerably. Imaging observations of metric radio emissions along with coronagraph observations have been used to obtain these results. We consider the following: (i) Why slow CMEs are associated with metric type IV radio emission contrary to the earlier belief, (ii) Why shocks piston driven by the CMEs are not seen in the solar corona, (iii) Thermal radio emission from the CMEs and their implications to CME-flare relationship and (iv) Radio signatures of coronas disconnection events. Title: Nobeyama Radio Observatory report, no. 361: The radio properties of solar active region soft x-ray transient brightenings Authors: White, S. M.; Kundu, M. R.; Shimizu, T.; Shibasaki, K.; Enome, S. Bibcode: 1995STIN...9529098W Altcode: We present the results of a search for radio emission from active-region transient brightenings identified in Yohkoh Soft X-ray Telescope observations of active region AR 7260. We present detailed observations of four events in which 17 GHz radio emission is clearly detected in observations by the Nobeyama Radioheliograph. The time profiles of the 17 GHz data are very similar to those of the soft X-ray fluxes, and the 17 GHz flux is very close to that expected from plasma with the temperature and emission measure derived for the soft X-ray-emitting material from filter ratios. No impulsive nonthermal radio emission was detected from any of the 4 events, although each was at least GOES class B1 in soft X-rays. Weak hard X-rays may have been detected by GRO/BATSE from the strongest of the events, but not from two others. These negative results leave open the possibility that there is a difference between active region transient brightenings and solar flares, in that the former do not convert a significant amount of the released energy into accelerated electrons. However, confirmation of this hypothesis will require a larger sample of events. Title: Polarization Features of Solar Radio Emission and Possible Existence of Current Sheets in Active Regions Authors: Gopalswamy, N.; Zheleznyakov, V. V.; White, S. M.; Kundu, M. R. Bibcode: 1994SoPh..155..339G Altcode: We show that it is possible to account for the polarization features of solar radio emission provided the linear mode coupling theory is properly applied and the presence of current sheets in the corona is taken into account. We present a schematic model, including a current sheet that can explain the polarization features of both the low frequency slowly varying component and the bipolar noise storm radiation; the two radiations face similar propagation conditions through a current sheet and hence display similar polarization behavior. We discuss the applications of the linear mode coupling theory to the following types of solar radio emission: the slowly varying component, the microwave radio bursts, metric type U bursts, and bipolar noise storms. Title: Transient Microwave Brightenings in Solar Active Regions: Comparison between VLA and YOHKOH Observations Authors: Gopalswamy, N.; Payne, T. E. W.; Schmahl, E. J.; Kundu, M. R.; Lemen, J. R.; Strong, K. T.; Canfield, R. C.; de La Beaujardiere, J. Bibcode: 1994ApJ...437..522G Altcode: We report observations of transient microwave (2 cm) brightenings and their relationship with brightenings in soft X-rays. The peak flux of the microwave brightenings observed by the Very Large Array (VLA) is smaller than the previously reported fluxes by two orders of magnitude. The microwave sources were highly polarized (up to 100%) and were situated on the periphery of a sunspot umbra. Among the many transients observed in X-rays by Yohkoh, two were observed simultaneously in microwaves. The microwave sources were found to be closer to the umbra of the sunspot than were the X-ray loops. It seems that the microwave sources are located at the footpoints of the looplike X-ray transients. Using the combined VLA, Yohkoh, and Mees data set, we determine the physical parameters of the loop in which the brightenings occur. We find that an increase in emission measure accompanied by small-scale heating can account for the X-ray brightening. The microwave emission can be interpreted as thermal gyroresonance or nonthermal gyrosynchrotron processes during the X-ray brightening. The magnetic field in the microwave-source region is found to be 1200-1800 G. The observations also provide evidence for temperature gradient in the coronal loops. Title: Detection of 17 GHz Radio Emission from X-Ray--bright Points Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N. Bibcode: 1994ApJ...431L.155K Altcode: Using observations made with the Nobeyama radio heliograph (NRH) at 17 GHz and the Yohkoh/SXT experiment, we report the first detection of 17 GHz signatures of coronal X-ray-bright points (XBPs). This is also the first reported detection of flaring bright points in microwaves. We have detected four BPs at 17 GHz out of eight identified in SXT data on 1992 July 31, for which we looked for 17 GHz emission. For one XBP located in a quiet mixed-polarity region, the peak times at 17 GHz and X-rays are very similar, and both are long-lasting-about 2 hr in duration. There is a second BP (located near an active region) which is most likely flaring also, but the time profiles in the two spectral domains are not similar. The other two 17 GHz BPs are quiescent with fluctuations superposed upon them. For the quiet region XBP, the gradual, long-lasting, and unpolarized emission suggests that the 17 GHz emission is thermal. Title: Metric Type III Bursts from Flaring X-ray Bright Points Authors: Kundu, M. R.; Strong, K. T.; Pick, M.; Harvey, K. T.; Kane, S. R.; White, S. M.; Hudson, H. S. Bibcode: 1994kofu.symp..343K Altcode: X-ray bright points (XBP's) are known to show variability on a number of timescales, including impulsive X-ray brightenings. The relationship between these XBP ``flares'' and normal solar flares is poorly known. A fundamental question is whether nonthermal acceleration of particles takes place in XBP flares. We address this issue by searching for nonthermal radio emission at metric wavelengths from flaring XBPs identified in Yohkoh/SXT data. Unequivocal evidence for type-III-like radio bursts, usually attributed to beams of nonthermal electrons on open field lines, is found. This suggests that XBP flares are similar to normal flares and can indeed accelerate nonthermal populations of energetic particles. Title: Evolution of an Active Region and Flare Productivity Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.; Bruner, M.; Sakao, T.; Kosugi, T. Bibcode: 1994kofu.symp..353K Altcode: We have studied the evolution of an active region (AR 7515) in terms of flare productivity. This region appears at the east limb on May 23, 1993 and then continues its onward march across the disk. We follow its evolution until June 2. This region produces many small flares. We study the topology, both magnetic and structural of the neighboring regions as observed at 17 GHz by the Nobeyama Radio Heliograph (NRH) and the Yohkoh/SXT to find their effects on the flare-producing AR. We investigate the spatial structure of the flaring region from 17 GHz and SXT maps during various times of the impulsive and decay phase, to understand the difference in the flaring region spatial structure during the preflare, impulsive and decay phases. In general, the maps made during these phases show several loops. We try to relate these flaring loops with the preflare active region structure. Title: Study of Active Region Magnetic Field Structures Using VLA Radio, YOHKOH X-ray and MEES Optical Observations Authors: Gopalswamy, N.; Schmahl, E. J.; Kundu, M. R.; Lemen, J. R.; Strong, K. T.; Canfield, R. C.; de La Beaujardiere, J. Bibcode: 1994kofu.symp..347G Altcode: We report on the observation of compact magnetic flux tubes from the boundary between the umbra and penumbra of a large sunspot in AR 7135 on April 24, 1992. The structure and geometry of one such flux tube was determined using the coordinated observations obtained by the Very Large Array, the Yohkoh Soft X-ray Telescope and the Mees Solar Observatory. From radio observations we infer that the magnetic field of the flux tube at the spot-side footpoint is ~ 1300-1800 G. Title: Observation of 17 GHz Radio Emission from X-ray Bright Points Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N. Bibcode: 1994kofu.symp...79K Altcode: Using observations made with the Nobeyama radio heliograph (NRH) at 17 GHz and the Yohkoh/SXT experiment, we report the first detection of 17 GHz signatures of coronal X-ray bright points (XBP's). This is also the first reported detection of flaring bright points in microwaves. We have detected four BP's at 17 GHz out of eight observed by SXT on July 31, 1992, for which we looked for 17 GHz emission. For one XBP located in a quiet mixed-polarity-region, the peak times at 17 GHz and X-rays are very similar, and both are long lasting -- at least 6 hours in duration. There is a second BP (located near an active region) which is most likely flaring also, but the time profiles in the two spectral domains are not similar. The other two 17 GHz BPs are quiescent with fluctuations superposed upon them. For the quiet region XBP, we believe that the 17 GHz emission is thermal. Title: Multiwavelength Observations of a Solar Flare Authors: White, S. M.; Silva, A.; de Pater, I.; Lin, R. P.; Gary, D. E.; Hudson, H. S.; Doyle, J. G.; Hagyard, M. J.; Kundu, M. R. Bibcode: 1994kofu.symp..203W Altcode: No abstract at ADS Title: The Radio Source around eta Carinae Authors: White, S. M.; Duncan, R. A.; Lim, J.; Nelson, G. J.; Drake, S. A.; Kundu, M. R. Bibcode: 1994ApJ...429..380W Altcode: We present high spatial resolution radio observations of the peculiar southern star Eta Carinae, made with the Australian Telescope. The images, at 8 and 9 GHz with a resolution of 1.0 arcsec show a source of dimension 10 arcsec and total flux of 0.7 Jy dominated by a strong central peak. The radio emission is unpolarized and offers no support to models which invoke degenerate stars or more exotic objects within the core of Eta Car. In these data we find no evidence for more than one energy source in the core with arcsecond separations as some infrared observations have suggested. Several levels of structure are evident in the radio image, which shows symmetry on the larger scales. Conventional formulae for stellar wind radio sources give a mass loss rate of order 3 x 10-4 Solar Mass/yr based on the radio flux in the central peak, which yields a wind momentum flux of order 20% of the momentum flux available from the star's radiation field. The radio emission at these frequencies is consistent with thermal emission from gas flowing away from a 'luminous blue variable' star (LBV) Eta Car is probably the brightest thermal stellar wind radio source in the sky. Title: Solar Cycle Variation of the Microwave Spectrum and Total Irradiance Authors: Schmahl, E. J.; Kundu, M. R. Bibcode: 1994SoPh..152..167S Altcode: 1994svs..coll..167S; 1994IAUCo.143..167S We have extended the proxy relationship between irradiance and microwaves by using the daily solar fluxes from Toyokawa Observatory at 1000, 2000, 3750 and 9400 MHz in addition to the Ottawa 2800 MHz flux for the years 1980-1989. It turns out that the flux at 1000 MHz is better correlated with irradiance than the flux at higher frequencies-an unexpected result. We have also found that the spectrum of the flux shows shape changes that are related to the number and type of active regions. Because of this the five-frequency spectral measurements of microwave flux allow one to separate the sunspot and coronal features, providing an improved proxy of solar variability. Title: Nonthermal Processes in Flaring X-Ray--bright Points Authors: Kundu, M. R.; Strong, K. T.; Pick, M.; White, S. M.; Hudson, H. S.; Harvey, K. L.; Kane, S. R. Bibcode: 1994ApJ...427L..59K Altcode: X-ray-bright point (XBPs) are known to show variability on a number of timescales, including impulsive X-ray brightenings. The relationship between these XBP 'flares' and normal solar flares is poorly known. A fundamental question is whether nonthermal acceleration of particles takes place in XBP flares. We address this issue by searching for nonthermal radio emission at metric wavelengths from flaring XBPs identified in Yohkoh soft x-ray telescope (SXT) data. Unequivocal evidence for type III-like radio bursts, usually attributed to beams of nonthermal electrons on open field lines, is found. This suggests that XBP flares are similar to normal flares and can indeed accelerate nonthermal populations of energetic particles. Title: Nonthermal Radio Emission Associated with a Coronal Disconnection Event Authors: Gopalswamy, N.; Kundu, M. R.; St. Cyr, O. C. Bibcode: 1994ApJ...424L.135G Altcode: We have found possible radio signatures of a coronal disconnection event observed by the Solar Maximum Mission Coronagraph/Polarimeter. The radio emission seems to be produced by charged particles accelerated during the same reconnection process which is responsible for the disconnection event. We discuss the implications of the radio emission characteristics to the reconnection process. Title: Three dimensional coronal structures using clark lake observations Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R. Bibcode: 1994AdSpR..14d..65S Altcode: 1994AdSpR..14...65S Throughout the quiet-Sun years 1982-1987, the Clark Lake Radioheliograph mapped the solar corona on a daily basis at frequencies from 30 to 100 MHz. The Clark Lake maps show a variety of features which we have analyzed quantitatively. Among the features are coronal streamers, which appear to cross the solar disk during a solar rotation. We have modeled the streamers with various geometrics and density profiles, and computed ray-tracing images for comparison with the CLRO maps. These models produced estimates of density and spatial scales in 3 dimensions for the streamers. We discuss the significance of these estimates and compare them with inferences made from optical observations. One of the possible conclusions we draw from these comparisons is that there are unresolved structures in stremers, not observable optically in the limb data. Title: Three Dimensional Coronal Structures Using Clark-Lake Observations Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R. Bibcode: 1994SoPh..150..325S Altcode: We have undertaken a study of coronal features observed at meter-decameter wavelengths using the Clark Lake radioheliograph. Among the coronal structures we have studied are the radio manifestations of coronal streamers on the solar disk and above the solar limb. We have analyzed the radio data quantitatively, using ray-tracing models for comparison with the maps. Our study provides information about the streamers' three-dimensional shapes, scales, and density profiles, for comparison with related observations using white-light coronagraphs. Title: Non-radial magnetic field structures in the solar corona Authors: Gopalswamy, N.; Kundu, M. R.; Raoult, A.; Pick, M. Bibcode: 1994SoPh..150..317G Altcode: We report on the structure and geometry of coronal magnetic fields inferred from the observations of meter-decimeter type III and moving type IV radio bursts, associated with a Hα flare. This is the first report of type III radio bursts from the Nançay radioheliograph after it acquired the two-dimensional multifrequency capability. Dispersion of the radio source positions with frequency suggests that open and closed field lines are considerably inclined to the radial direction which is consistent with the connectivity observed in the magnetogram. We suggest that multiple arch systems are involved in the type IV emission. From the polarization and dispersion characteristics of the type IV source, we infer that the emission is due to fundamental plasma emission. Title: Pulsed Acceleration in Solar Flares Authors: Aschwanden, Markus J.; Benz, Arnold O.; Dennis, Brian R.; Kundu, Mukul R. Bibcode: 1994ApJS...90..631A Altcode: 1994IAUCo.142..631A We study the nonlinear dynamics of particle acceleration in solar flares by analyzing the time series of various quasi-periodic radio signatures during flares. In particular we present the radio and hard X-ray data of three flares which suppport the following tentative conclusions: (1) Particle acceleration and injection into magnetic structures occurs intrinsically in a pulsed mode (with a typical period of 1-2 s), produced by a single, spatially coherent, nonlinear system, rather than by a stochastic system with many spatially independent components ('statistical flare' produced by a fragmented primary energy release). (2) The nonlinear (quasi-periodic) mode of pulsed particle acceleration and injection into a coronal loop can be stabilized by phase locking with an MHD wave (oscillation) mode, if both periods are close to each other. (3) Pulsed injection of electron beams into a coronal loop may trigger nonlinear relaxational oscillations of wave-particle interactions. This is particularly likely when the limit cycles of both systems are similar. Title: Eta Carinae Authors: White, S.; Duncan, R.; Drake, S.; Lim, J.; Kundu, M. Bibcode: 1994IAUC.5932....2W Altcode: 1994IAUC.5932....1W S. White, University of Maryland; R. Duncan, Australia Telescope; S. Drake, Goddard Space Flight Center; J. Lim, California Institute of Technology; and M. Kundu, University of Maryland, report: "Australia Telescope observations of the luminous blue variable eta Car show that it is undergoing a radio outburst, with the flux having doubled in the last 7 months and apparently still increasing. It is currently a 2-Jy radio source at 9 GHz. The rise in flux is associated with the appearance of a new feature in the radio images, about 1".1 northwest of the radio source attributed to the stellar wind and almost as bright. Assuming that this feature is due to a gas clump ejected asymmetrically by the star and radiating thermal free-free emission, the minimum mass involved is 0.005 solar mass. Infrared observations to follow the history of dust formation in this gas clump would be valuable." Title: Observing Stellar Coronae with the Goddard High Resolution Spectrograph. I. The dMe Star AU Microscopii Authors: Maran, S. P.; Robinson, R. D.; Shore, S. N.; Brosius, J. W.; Carpenter, K. G.; Woodgate, B. E.; Linsky, J. L.; Brown, A.; Byrne, P. B.; Kundu, M. R.; White, S.; Brandt, J. C.; Shine, R. A.; Walter, F. M. Bibcode: 1994ApJ...421..800M Altcode: We report on an observation of AU Mic taken with the Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope. The data consist of a rapid sequence of spectra covering the wavelength range 1345-1375 A with a spectral resolution of 10,000. The observations were originally intended to search for spectral variations during flares. No flares were detected during the 3.5 hr of monitoring. A method of reducing the noise while combining the individual spectra in the time series is described which resulted in the elimination of half of the noise while rejecting only a small fraction of the stellar signal. The resultant spectrum was of sufficient quality to allow the detection of emission lines with an integrated flux of 10-15 ergs/sq cm(sec) or greater. Lines of C I, O I, O V, Cl I, and Fe XXI were detected. This is the first indisputable detection of the 1354 A Fe XXI line, formed at T approximately = 107 K, on a star other than the Sun. The line was well resolved and displayed no significant bulk motions or profile asymmetry. From the upper limit on the observed line width, we derive an upper limit of 38 km/s for the turbulent velocity in the 107 K plasma. An upper limit is derived for the flux of the 1349 A Fe XII line, formed at T approximately = 1.3 x 106 K. These data are combined with contemporaneous GHRS and International Ultraviolet Explorer (IUE) data to derive the volume emission measure distribution of AU Mic over the temperature range 104-107 K. Models of coronal loops in hydrostatic equilibrium are consistent with the observed volume emission measures of the coronal lines. The fraction of the stellar surface covered by the footprints of the loops depends upon the loop length and is less than 14% for lengths smaller than the stellar radius. From the upper limit to the estimated width of the Fe XXI line profile we find that the we cannot rule out Alfven wave dissipation as a possible contributor to the required quiescent loop heating rate. Title: Millimeter, Microwave, Hard X-Ray, and Soft X-Ray Observations of Energetic Electron Populations in Solar Flares Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J. Bibcode: 1994ApJS...90..599K Altcode: 1994IAUCo.142..599K We present comparisons of multiwavelength data for a number of solar flares observed during the major campaign of 1991 June. The different wavelengths are diagnostics of energetic electrons in different energy ranges: soft X-rays are produced by electrons with energies typically below 10 keV, hard X-rays by electrons with energies in the range 10-200 keV, microwaves by electrons in the range 100 keV-1 MeV, and millimeter-wavelength emission by electrons with energies of 0.5 MeV and above. The flares in the 1991 June active period were remarkable in two ways: all have very high turnover frequencies in their microwave spectra, and very soft hard X-ray spectra. The sensitivity of the microwave and millimeter data permit us to study the more energetic (greater than 0.3 MeV) electrons even in small flares, where their high-energy bremsstrahlung is too weak for present detectors. The millimeter data show delays in the onset of emission with respect to the emissions associated with lower energy electrons and differences in time profiles, energy spectral indices incompatible with those implied by the hard X-ray data, and a range of variability of the peak flux in the impulsive phase when compared with the peak hard X-ray flux which is two orders of magnitude larger than the corresponding variability in the peak microwave flux. All these results suggest that the hard X-ray-emitting electrons and those at higher energies which produce millimeter emission must be regarded as separate populations. This has implications for the well-known 'number problem' found previously when comparing the numbers of non thermal electrons required to produce the hard X-ray and radio emissions. Title: Radio Constraints on Coronal Models for dMe Stars Authors: White, S. M.; Lim, J.; Kundu, M. R. Bibcode: 1994ApJ...422..293W Altcode: Radio data are used to test coronal models for dMe stars. Specifically, we show that photospheric magnetic field observations imply that the low corona of a dMe star should be saturated by magnetic fields with an average strength in excess of 1 kG. In such fields the hot component of the corona detected in X-ray observations (temperature of order 2 x 107 K) would be optically thick at least up to 15 GHz due to thermal gyroresonance opacity. The resulting emission would easily be detectable by radio observations and should have a radio spectrum rising in the microwave range. We have carried out observations to test this prediction, and in the majority of cases find that the observed fluxes at 15 GHz are too low to be consistent with the assumptions. In the few cases where the stars were detected at 15 GHz, the evidence indicates that the observed emission is nonthermal. These results imply that the hot component of the X-ray-emitting plasma in the corona is not coincident with the strong magnetic fields in the lower corona. Because the hot plasma must still be confined by closed magnetic field lines, it is likely to be restricted to heights of the order of a stellar radius above the photosphere. The results seem to imply a different genesis for the two components of the X-ray-emitting corona of flare stars: the hot component may be cooling flare plasma, while the cooler component (temperature of order 3 x 106 K) is associated with a more conventional coronal heating mechanism. Title: Observations of the 1991 Eclipse at 3.5 MM Wavelength Authors: White, S. M.; Kundu, M. R. Bibcode: 1994IAUS..154..167W Altcode: No abstract at ADS Title: Interferometry of Solar Flares at 3-mm Wavelength Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J. Bibcode: 1994IAUS..154..131K Altcode: No abstract at ADS Title: The Effects of Largescale and Smallscale Density Structures on the Radio Emission from Coronal Streamers Authors: Thejappa, G.; Kundu, M. R. Bibcode: 1994SoPh..149...31T Altcode: The radio observations of the coronal streamers obtained using Clark Lake radioheliograph at 73.8, 50.0, and 38.5 MHz during a period of minimum activity in September 1986 are presented. Streamers appear to correlate with two prominent disk sources whose intensities fluctuated randomly. The variations in half-power diameter of the radio Sun are found to correspond with the variations in the white-light extents of the coronal streamers. It appears that the shape of the radio Sun is not a function of the phase of the solar cycle; instead it depends on the relative positions of the streamers in the corona. The observed peak brightness temperatures,TB, of the streamers are found to be very low, being ≃6 × 104 K. Title: A Search for gamma-Ray Emission from Active Stars Authors: White, S. M.; Harmon, B. A.; Lim, J.; Kundu, M. R. Bibcode: 1994ASPC...64..498W Altcode: 1994csss....8..498W No abstract at ADS Title: VLA Observations of a High Coronal Flare Authors: Raulin, J. P.; Gopalswamy, N.; Kundu, M. R.; Nitta, N. Bibcode: 1993AAS...183.0706R Altcode: 1993BAAS...25.1300R We present radio observations of a coronal flare which occurrred on 1993 April 22, in a weak magnetic field region to the west of AR 7477. The observations were made by the Very Large Array (VLA) at 20 and 90 cm. The event consists of bright (brightness temperature of 10(10) K) unpolarized bursts, followed by a longlasting unpolarized continuum with moderately high brightness temperature (2-3 10(9) K) in the high corona (90 cm observations). The low coronal counterpart of this flare is a weak and moderatly polarized 20 cm radio emission. Full disk Yohkoh images show that the corresponding radio emission is located in or above magnetic loops connecting AR 7477 and its neighborhood. The presence of permanent and non-varying noise storm associated with AR 7477 seems to indicate that the overall magnetic field structure of the active region is unaffected by the flare. The coronal radio source which is indicative of acceleration of electrons to nonthermal energies, is not associated with major Hα emissio n nor with bright X ray emission. The absence of any detectable circular polarization, as well as the high brightness temperature, seems to indicate that the 90 cm emission is second harmonic plasma emission. Title: Variability in Sunspot Associated Microwave Emission: Umbral Oscillations? Authors: Gopalswamy, N.; Schmahl, E. J.; Kundu, M. R. Bibcode: 1993AAS...183.6808G Altcode: 1993BAAS...25.1396G We report on microwave observations of sunspot associated emission that shows variability over a time scale of minutes. To our knowledge, this is the first time such rapid variability has been observed in microwave radiation from a sunspot. These observations were obtained by the Very Large Array (VLA) on April 24, 1992 at 2cm. The radio emission from the sunspot umbra was in the form of several compact sources with a size less than 4 arcsec. The time evolution of the peak flux of these sources showed significant time variations which were sometimes periodic. The period of these ocillations was approximately 3 min, similar to that of intensity and Doppler shift oscillations observed in optically thin, transition region lines such as C IV (1548.19 Angstroms) in sunspot umbrae. There were also morphological changes in the extended sunspot emission over which the compact sources were superposed. We also observed the appearance of new compact sources within the umbra where there was reduced emission before. The brightness temperatures of these compact sources were in the range (1-5)times 10(5) K. We explore possible interpretations of the time variability. Title: Evolution of a Solar Active Region and Flare Productivity Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.; Bruner, M. Bibcode: 1993AAS...183.6807K Altcode: 1993BAAS...25.1396K We have studied the evolution of an active region (AR 7515) in terms of flare productivity. This region appeared on the east limb on May 23, 1993 and continued its onward march across the disk. We followed its evolution until June 2. This region produced many small flares. We studied the topology, both magnetic and structural of the flaring region as observed at 17 GHz by the Nobeyama radio Heliograph (NRH) with a spatial resolution of 10 arcsec and the Yohkoh SXT which has a spatial resolution of 2.5 arcsec. Among other things, we find: (i) Frequently a flare starts with the appearance of a new region/loop which interacts with a pre-existing loop; this interaction acta as a flare trigger. (ii) There appear to exist multiple sets of interacting loops in the same active region. Different bursts on the same day seem to come from diffrent sets of interacting loops. (iii) Sometimes two or more sets of interacting loops can activate at the same time, giving rise to different peaks in the same burst. In the decay phase of some bursts there may appear a new or reactivated region/loop which becomes the source of new burst emission. (iv) A simple spiky burst in general originates from a narrow region and by implication from a compact set of interacting loops. Title: Evidence for Ordinary Mode Emission from Microwave Bursts Authors: Alissandrakis, C. E.; Nindos, A.; Kundu, M. R. Bibcode: 1993SoPh..147..343A Altcode: We analyze high-resolution, one-dimensional observations of simple microwave bursts, obtained at 4.9 GHz with the Westerbork Synthesis Radio Telescope in 1980, together with Hα photographs of the associated flares from the Observatories of Athens and Meudon. In most cases the polarization structure can be interpreted in terms of extraordinary mode emission, taking into account the polarity of the underlying magnetic field and propagation effects, which may lead to inversion of the sense of polarization in the limbward part of the flaring loop. We found evidence for ordinary mode emission in two classes of events. In one class theo-mode comes from regions overlying strong magnetic field, which we interpret in terms of thermal gyroresonance absorption of the extraordinary mode at the third harmonic of the gyrofrequency. In the other class the entire burst emits in theo-mode, which may be attributed to high gyrosynchrotron optical depth. Title: Structure of a fast coronal mass ejection from radio observations. Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1993AdSpR..13i..75G Altcode: 1993AdSpR..13R..75G The authors investigate the thermal structure of a coronal mass ejection (CME) in meter-dekameter wavelengths and compare it with the optical evidence. The multifrequency observations enable us to infer the three dimensional structure of the CME. The authors estimated the mass of the CME and found to be in reasonable agreement with the range of values obtained from white light observations. Title: Interferometric observations of solar flares at 3 mm wavelength Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J. Bibcode: 1993AdSpR..13i.289K Altcode: 1993AdSpR..13..289K We report on the observations of a number of flares at a wavelength of 3.5 mm during the 1991 June solar campaign. Many flares, including small ones, show an impulsive phase at milllimeter wavelengths which indicates the presence of MeV electrons, and the millimeter observations are far more sensitive to such electrons than are current γ-ray detectors. However, these energetic electrons do not always show a good correlation with the lower-energy electrons which produce hard X-rays below 100 keV. The production efficiency of MeV electrons seems to vary considerably from flare to flare. An extended phase similar to the soft X-ray behaviour is also seen at millimeter wavelengths, which we attribute to dense hot material radiating thermal bremsstrahlung. In the impulsive onset the millimeter emission seems to be consistently delayed with respect to the hard X-rays. Title: Simultaneous Observations of Solar Plage with the Solar Extreme Ultraviolet Rocket Telescope and Spectrograph (SERTS), the VLA, and the Kitt Peak Magnetograph Authors: Brosius, Jeffrey W.; Davila, Joseph M.; Thompson, William T.; Thomas, Roger J.; Holman, Gordon D.; Gopalswamy, N.; White, Stephen M.; Kundu, Mukul R.; Jones, Harrison P. Bibcode: 1993ApJ...411..410B Altcode: We obtained simultaneous images of solar plage on 1991, May 7 with SERTS, the VLA,4 and the NASA/National Solar Observatory spectromagnetograph at the NSO/Kitt Peak Vacuum Telescope. Using intensity ratios of Fe XVI to Fe XV emission lines, we find that the coronal plasma temperature is (2.3-2.9) x 10 exp 6 K throughout the region. The column emission measure ranges from 2.5 x 10 exp 27 to l.3 x 10 exp 28 cm exp -5. The calculated structure and intensity of the 20 cm wavelength thermal bremsstrahlung emission from the hot plasma observed by SERTS is quite similar to the observed structure and intensity of the 20 cm microwave emission observed by the VLA. Using the Meyer (1991, 1992) revised coronal iron abundance, we find no evidence either for cool absorbing plasma or for contributions from thermal gyroemission. Using the observed microwave polarization and the SERTS plasma parameters, we calculate a map of the coronal longitudinal magnetic field. The resulting values, about 30-60 G, are comparable to extrapolated values of the potential field at heights of 5000 and 10,000 km. Title: Meter-Wave Radio Emission from Flaring X-ray Bright Points Authors: Kundu, M. R.; Strong, K. T.; Pick, M.; Kane, S. R.; Harvey, K.; White, S. M. Bibcode: 1993BAAS...25.1180K Altcode: No abstract at ADS Title: A Study of the Solar Active Regions Using Simultaneous VLA and Yohkoh Soft X-ray Imaging: CoMStOC `92 Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.; Lemen, J. R.; Strong, K. T.; Schmelz, J. T. Bibcode: 1993BAAS...25R1213G Altcode: No abstract at ADS Title: Hard X-ray and Radio Spectra for Solar Flares from AR 6659 Authors: White, S. M.; Murphy, R.; Schwartz, R. A.; Kundu, M. R.; Gopalswamy, N.; Lim, J. Bibcode: 1993BAAS...25Q1222W Altcode: No abstract at ADS Title: VLA and Yohkoh Observations of an M1.5 Flare Authors: Gopalswamy, N.; Kundu, M. R.; Lemen, J. R.; Nitta, N.; Strong, K. T. Bibcode: 1993BAAS...25.1186G Altcode: No abstract at ADS Title: Millimeter, Microwave and X-Ray Morphology and Spectra of the 07Jan92 Flare Authors: Silva, A. V.; Lin, R. P.; de Pater, I.; White, S. M.; Kundu, M. R.; Gary, D. E.; Hudson, H. S. Bibcode: 1993BAAS...25Q1223S Altcode: No abstract at ADS Title: VLA, OVRO, Yohkoh and Optical Observations During CoMStOC Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.; Lemen, J.; Strong, K. T.; de La Beaujardiere, J. Bibcode: 1993BAAS...25.1213S Altcode: No abstract at ADS Title: Solar Coronal Plasma and Magnetic Field Diagnostics Using SERTS and Coordinated VLA Observations Authors: Brosius, J. W.; Davila, J. M.; Thompson, W. T.; Thomas, R. J.; Holman, G. D.; Gopalswamy, N.; White, S. M.; Kundu, M. R.; Jones, H. P. Bibcode: 1993BAAS...25.1224B Altcode: No abstract at ADS Title: A Multiwavelength Portrait of a Solar Active Region Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N. Bibcode: 1993BAAS...25.1183W Altcode: No abstract at ADS Title: The Radio Source Around eta Carinae Authors: White, S. M.; Duncan, R. A.; Lim, J.; Nelson, G. J.; Drake, S. A.; Kundu, M. R. Bibcode: 1993AAS...182.3906W Altcode: 1993BAAS...25..858W The first high--spatial--resolution (1{('') }) radio image of the source surrounding the famous massive southern star eta Carinae has been obtained with the Australia Telescope. The image shows a number of interesting features: a strong central peak; ridges of emission close to the peak and extending away from it in the directions of putative ``jets'' seen in the HST image of the region, and also other ridges in the directions of the lobes of the Homunculus; a box--like extended feature of dimension 7{('') } \ times 5{('') }, with its major axis orthogonal to the major axis of the Homunculus; and two fainter lobes extending to 5{('') } \ from the star in the directions of both lobes of the Homunculus. The radio image bears a strong resemblance to the high--resolution infra--red images of the region around the star. No radio emission associated with the more extended X-ray--emitting nebula is detected. The current rate of mass loss from the star is estimated, and physical conditions within the nebula are discussed. Title: Spectral observations of active region sources with RATAN-600 and WSRT Authors: Alissandrakis, C. E.; Gel'Frejkh, G. B.; Borovik, V. N.; Korzhavin, A. N.; Bogod, V. M.; Nindos, A.; Kundu, M. R. Bibcode: 1993A&A...270..509A Altcode: We present spectral observations of neutral line and sunspot associated sources obtained with the RATAN-600 radio telescope and the WSRT in the wavelength range of 2 to 6 cm. Sources associated with large sunspots have flat spectra, while neutral line sources have very steep spectra. In the case of a large spot we estimated the magnetic field to be at least 2700 G at the base of the transition region and 1800 G in the low corona. We consider possible interpretations of the radio emission above the neutral lines. Gyroresonance emission at the fourth harmonic is inadequate, whereas emission from a small population of nonthermal electrons (total number 10 exp 30 to 10 exp 31) with a delta = 3 power law distribution seems to be sufficient. Title: Thermal and nonthermal emissions during a coronal mass ejection Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1993SoPh..143..327G Altcode: We report on the thermal and nonthermal radio emissions from a coronal mass ejection (CME) observed at meter-decameter wavelengths using the Clark Lake multifrequency radioheliograph. From white-light observations of the Solar Maximum Mission Coronagraph/Polarimeter instrument the CME was found to have a speed of ∼ 450 km s−1. Since there was no nonthermal radio emission in the beginning of the event and the one which occurred later was quite weak, we were able to observe the thermal structure of the CME in radio. Type III bursts and a nonthermal continuum started several minutes after the CME onset. We use the radio and optical observations to show that the CME was not driven by the flare. We investigate the thermal structure and geometry of the mass ejection in radio and compare it with the optical evidence. Finally we develop a schematic model of the event and point out that particle acceleration high in the corona is possible. Title: A 1.5 GHz Radio Survey of the Hyades Open Stellar Cluster Authors: White, S. M.; Jackson, P. D.; Kundu, M. R. Bibcode: 1993AJ....105..563W Altcode: Results of a radio survey of the Hyades open stellar cluster carried out with the VLA at 1.5 GHz are reported. Seventeen fields containing over 150 cataloged stars were mapped down to a limiting sensitivity ranging from 0.3 mJy at the centers of the fields to 0.9 mJy at a distance of 20 arcmin from field centers. Two stars were detected as radio sources: the evolved spectroscopic binary V471 Tau, consisting of a white dwarf and a red dwarf; and the apparently premain-sequence G+K star spectroscopic binary HD 27130. The failure to detect any single stars as radio sources is generally consistent with the age-rotation-activity paradigm, according to which stellar activity is due to magnetic fields produced by dynamo action in rapidly rotating stars and should decrease with age as a star spins down due to magnetic braking. It is concluded that the Hyades M dwarf population is not more active at radio wavelengths than the nearby flare star population, or else the number of flare stars in the Hyades is much less than presently assumed. Title: Analysis of EUV, Microwave and Magnetic Field Observations of Solar Plage Authors: Brosius, J. W.; Davila, J. M.; Jones, H. P.; Thompson, W. T.; Thomas, R. J.; Holman, G. D.; White, S. W.; Gopalswamy, N.; Kundu, M. R. Bibcode: 1993ASPC...46..291B Altcode: 1993mvfs.conf..291B; 1993IAUCo.141..291B No abstract at ADS Title: Radio observations of coronal streamers. Authors: Kundu, Mukul R. Bibcode: 1992ESASP.348...87K Altcode: 1992cscl.work...87K The author presents some radio observations of coronal streamers, obtained at meter-decameter wavelengths, using the Clark Lake multifrequency radioheliograph. Using daily imaging observations he has generated synoptic charts similar to white light coronagraph synoptic charts, and compared radio brightness enhancements with bright coronal streamers. By using several frequencies simultaneously, it has been possible to construct three-dimensional structures of coronal streamers. The author shows that type III producing electrons propagate in coronal streamers. He also compares the relative positions of type III burst sources and coronal streamers as observed by HAO C/P experiment aboard SMM; infers the paths of type III-emitting electrons in dense coronal streamers, and from multi-frequency observations derives electron density distributions above active regions near the limb. Title: Observations of stationary radio sources: coronal polar plumes? Authors: Gopalswamy, Natchimuthkonar; Schmahl, Edward J.; Kundu, Mukul R. Bibcode: 1992ESASP.348..113G Altcode: 1992cscl.work..113G Weak stationary radio sources are often observed near the poles of the Sun during solar minimum in the two dimensional radio images at meter-decameter wavelengths. The authors present observations from the Clark Lake multifrequency radioheliograph obtained during Carrington rotation 1771 (Jan 14 to Feb 10, 1986) and 1785 (Jan 31 to Feb 25, 1987). They explore various possibilities to interpret these stationary sources involving thermal and nonthermal emissions from polar plumes. Title: Models of coronal streamers at meter-decameter wavelengths. Authors: Schmahl, Edward J.; Gopalswamy, Natchimuthkonar; Kundu, Mukul R. Bibcode: 1992ESASP.348..145S Altcode: 1992cscl.work..145S Throughout the quiet Sun years 1982 - 1987, the Clark Lake radioheliograph routinely mapped the solar corona on a daily basis at frequencies from 30 to 100 MHz. The Clark Lake maps show a variety of features which are analyzed quantitatively. Among the features are coronal streamers, which appear to cross the solar disk during a solar rotation. The authors have modeled the streamers with various geometries and computed ray-tracing images for comparison with the CLRO maps. The best fitting streamer models have a density profile ≍5 times Saito (1970) with a background ≍0.1 times Saito. The required low background value may be explained by either scattering on "microstructure" or unresolved "macrostructure". Title: Solar Observations with a Millimeter Wavelength Array Authors: White, S. M.; Kundu, M. R. Bibcode: 1992SoPh..141..347W Altcode: Rapid developments in the techniques of interferometry at millimeter wavelengths now permit the use of telescope arrays similar to the Very Large Array at microwave wavelengths. These new arrays represent improvements of orders of magnitude in the spatial resolution and sensitivity of millimeter observations of the Sun, and will allow us to map the solar chromosphere at high spatial resolution and to study solar radio burst sources at millimeter wavelengths with high spatial and temporal resolution. Here we discuss the emission mechanisms at millimeter wavelengths and the phenomena which we expect will be the focus of such studies. We show that the flare observations study the most energetic electrons produced in solar flares, and can be used to constrain models for electron acceleration. We discuss the advantages and disadvantages of millimeter interferometry, and in particular focus on the use of and techniques for arrays of small numbers of telescopes. Title: Are coronal type II shocks piston driven? Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1992AIPC..264..257G Altcode: 1992pacp.work..257G Flare blast waves and shocks piston driven by coronal mass ejections (CMEs) have been proposed to be responsible for generating type II radio bursts in the solar corona. The idea for piston-driven shocks came primarily from temporal association of shocks and CMEs. Our compilation of CME events with simultaneous radio observations with positional information supports idea of flare blast waves. Title: The High-Frequency Characteristics of Solar Radio Bursts Authors: Lim, J.; White, S. M.; Kundu, M. R.; Gary, D. E. Bibcode: 1992SoPh..140..343L Altcode: We compare the millimeter, microwave, and soft X-ray emission from a number of solar flares in order to determine the properties of the high-frequency radio emission of flares. The millimeter observations use a sensitive interferometer at 86 GHz which offers much better sensitivity and spatial resolution than most previous high-frequency observations. We find a number of important results for these flares: (i) the 86 GHz emission onset appears often to be delayed with respect to the microwave onset; (ii) even in large flares the millimeter-wavelength emission can arise in sources of only a few arc sec dimension; (iii) the millimeter emission in the impulsive phase does not correlate with the soft X-ray emission, and thus is unlikely to contain any significant thermal bremsstrahlung component; and (iv) the electron energy distributions implied by the millimeter observations are much flatter (spectral indices of 2.5 to 3.6) than is usual for microwave or hard X-ray observations. Title: Unusually Low Coronal Radio Emission at the Solar Minimum Authors: Thejappa, G.; Kundu, M. R. Bibcode: 1992SoPh..140...19T Altcode: We present two-dimensional observations of the quiet Sun at 73.8, 50.0, and 38.5 MHz obtained with the Clark Lake Radioheliograph during the sunspot minimum period of September 1986. The observed peak brightness temperatures during the entire period of sunspot minimum are found to be extremely low, lying in the range (0.6 × 105 K − 2.5 × 105 K). It is shown that these low values cannot be explained by the generally adopted models for Ne and Te in a homogeneous corona. The effect of scattering by random density fluctuations is introduced in order to decrease the values of predicted Tb. The value of peak Tb is computed as a function of relative r.m.s. density fluctuations ε = <ΔNe>/Ne; and it is found that ɛ should be in the range from 0.07 to 0.19, 0.1 to 0.25, and 0.15 to 0.35, respectively, at 38.5, 50.0, and 73.8 MHz, respectively, to explain the observed low brightness temperatures. Title: Radio flares and magnetic fields on weak-line T Tauri stars. Authors: White, S. M.; Pallavicini, R.; Kundu, M. R. Bibcode: 1992A&A...259..149W Altcode: We report the first detection of circular polarization in the radio emission of two weak-line T Tauri stars. This is direct confirmation of the presence of magnetic fields in the coronae of these stars. The degree of polarization at 5 GHz is small, consistent with previous observations which did not find measurable polarization. We have also observed a radio flare on one of the two stars. The rising spectrum of the radio emission together with the low degree of polarization are strong evidence that radio outbursts on this class of stars are due to nonthermal gyrosynchrotron emission which is optically thick in the microwave range. One of the two stars shows no evidence for circumstellar material, and thus can be classified as 'naked'. However the other apparently has a dust disk, and the evidence of flaring on this star indicates that the mechanism involved does not require an empty circumstellar environment. Title: Analysis of EUV, Microwave, and Magnetic Field Observations of a Solar Active Region Authors: Brosius, J. W.; Davila, J. M.; Jones, H. P.; Thompson, W. T.; White, S. M.; Gopalswamy, N.; Kundu, M. R. Bibcode: 1992AAS...180.4002B Altcode: 1992BAAS...24R.792B No abstract at ADS Title: Simultaneous Hard X-ray, Soft X-ray, Millimeter and Microwave Observations of a Solar Flare Authors: White, S. M.; Kundu, M. R.; Lim, J.; Gopalswamy, N. Bibcode: 1992AAS...180.4504W Altcode: 1992BAAS...24..802W We present non-imaging data across a wide range of wavelengths for a solar flare which occurred on 1991 June 13. This flare is of interest because it shows a spike in hard X-rays at the beginning of the event which had a relatively hard X-ray spectrum, and was followed by a much softer impulsive phase. We present the BATSE and OSSE observations (from the Gamma Ray Observatory): the former have good time resolution, while the latter provide well-resolved spectral information. These are contrasted with the GOES soft-X-ray data on the hot thermal component in the corona, and radio observations up to 86 GHz which are sensitive to both the nonthermal and thermal components of the flare. The 86 GHz data from the BIMA millimeter interferometer show a spike in the impulsive phase coincident with the hard X-ray spike above 100 keV, as well as a long-duration thermal phase which appears to be consistent with an origin in the same material seen by GOES. We discuss the implications of the observations for particle acceleration in this flare. Title: Estimation of the Mass of a Coronal Mass Ejection from Radio Observations Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1992ApJ...390L..37G Altcode: The mass of a coronal mass ejection (CME) is estimated using meter-decametric observations obtained with the Clark Lake multifrequency radioheliograph. Mass estimates in the past were made using coronagraph and white-light photometer observations. Since the radiation at radio and optical wavelength regimes has different physical origins, the radio method can provide an independent check on the mass estimates. The estimate of the 1986 February 16 CME using the radio method is close to the average value of CME masses reported in the literature. Title: Millimeter Observations of Solar Flares Authors: Silva, A. V.; Lin, R. P.; de Pater, I.; White, S. M.; Kundu, M. R. Bibcode: 1992AAS...180.4510S Altcode: 1992BAAS...24..803S No abstract at ADS Title: Radio Observations During the 1991 June Campaign of Max'91 in Conjunction with Compton GRO Experiments Authors: Kundu, M. R. Bibcode: 1992AAS...180.3403K Altcode: 1992BAAS...24R.783K A summary of all available radio observations made during the 1991 June campaign of the MAX '91/Flare 22 program will be presented. The presentation will be concerned primarily with millimeter wavelength (BIMA and Nobeyama) and centimeter wavelengths (Owens Valley and Nobeyama) observations. Emphasis will be given to the question of millimeter observations as a diagnostic for Mev electrons in solar flares (gamma ray flares --- BATSE and OSSE data), millimeter emission occurring at the steep rise phase of hard X-ray emitting electrons (BATSE data) and delay of millimeter emission onset and 25-100 Kev X-rays (BATSE data). Implications of these results for generation of millimeter emission and particle acceleration process will be discussed. The Nobeyama data consist of non-imaging patrol observations at several frequencies in the frequency range 1--80 GHz, and Owens Valley data were obtained using the frequency agile interferometer in the frequency range 1--18 GHz. Light curves and spectral information of the most energetic flares will be presented. Title: 2-cm Observations of Quiescent and Flaring Emission from a Solar Active Region Authors: Lim, J.; White, S. M.; Kundu, M. R. Bibcode: 1992AAS...180.1102L Altcode: 1992BAAS...24..746L We present 2-cm images of a solar active region comprising a large leading spot and several smaller trailing spots, observed with the VLA on 1989 Dec 14 and 16. On both days, slowly-varying quiescent emission and impulsive flaring emission were detected. Comparisons of the radio images with white-light pictures and magnetograms obtained on Dec 13 and 17 revealed that the quiescent emission originated almost entirely from above the penumbra of large spots, whereas the flaring emission originated from regions of complex magnetic field topology near but not necessarily above magnetic neutral lines. The most intense source of quiescent emission had a relatively low brightness-temperature ( ~ 10(5) K), was highly circularly polarized (ranging from about 30\ trailing edge (i.e., limbward side) of the large leading spot. We discuss models for this emission, constrained by the low brightness temperature but high polarization. The weaker flare of Dec 14 showed a single resolved source, and was weakly circularly-polarized. The stronger flare of Dec 16 comprised a strong source with multiple peaks and several weaker compact sources, all with low degrees of circular polarization. Snapshot images of this flare showed an elongated feature moving rapidly away from the main region of emission and joining with the compact sources. We discuss likely mechanisms for this feature, and emission process(es) responsible for the flares. Title: The Structure of the Corona of dMe Flare Stars Authors: White, S. M.; Lim, J.; Kundu, M. R. Bibcode: 1992AAS...180.6005W Altcode: 1992BAAS...24..826W There is now considerable information on both the surface magnetic fields of dMe flare stars and on the thermal (X-ray emitting) populations in their coronae. We show that the simplest picture of the corona of a dMe flare star based on the measured photospheric magnetic field strengths, the measured filling factors of these fields, and the X-ray emission from their coronae, are inconsistent with radio observations of the coronae. We discuss possible resolutions of this dilemma. Title: A 5GHz radio survey of selected POST T Tauri and naked T Tauri stars. Authors: White, S. M.; Pallavicini, R.; Kundu, M. R. Bibcode: 1992A&A...257..557W Altcode: Results of a radio survey of weak-lined T Tauri (variably classified as either post T Tauri or naked T Tauri) stars at 5 GHz are reported. Thirty-two targets, chosen on the basis of known high-activity levels or youth indications, were observed, and 15, including eight previously unknown radio sources, were detected. It is suggested that most weak-lined T Tauris with high activity levels, e.g., as indicated by a high X-ray flux, are likely to be detectable radio sources at some time, but the radio emission goes through high and low phases. For the subsample of 14 stars observed in Taurus-Auriga which were thoroughly studied at IR, optical, and X-ray wavelengths, a clear association is found between radio activity and youth. Title: Observations on Mode Coupling in the Solar Corona and Bipolar Noise Storms Authors: White, S. M.; Thejappa, G.; Kundu, M. R. Bibcode: 1992SoPh..138..163W Altcode: We review high-spatial-resolution observations of the Sun which reflect on the role of mode coupling in the solar corona, and present a number of new observations. We show that typically polarization inversion is seen at 5 GHz in active region sources near the solar limb, but not at 1.5 GHz. Although this is apparently in contradiction to the simplest form of mode coupling theory, in fact it remains consistent with current models for the active region emission. Microwave bursts show no strong evidence for polarization inversion. We discuss bipolar noise storm continuum emission in some detail, utilizing recent VLA observations at 327 MHz. We show that bipolar sources are common at 327 MHz. Further, the trailing component of the bipole is frequently stronger than the leading component, in apparent conflict with the `leading-spot' hypothesis. The observations indicate that at 327 MHz mode coupling is apparently strong at all mode-coupling layers in the solar corona. The 327 MHz observations require a much weaker magnetic field strength in the solar corona to explain this result than did earlier lower-frequency observations: maximum fields are 0.2 G. This is a much weaker field than is consistent with current coronal models. Title: High Dynamic Range Multifrequency Radio Observations of a Solar Active Region Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N. Bibcode: 1992ApJS...78..599W Altcode: High-dynamic-range multifrequency radio observations of a solar active region are presented. The evolution of the region is followed at 5 GHz as it rotates from the limb to disk center, and when it is at disk center, observations at 0.33, 1.5, 5, 8.4, and 15 GHz are used to analyze the distribution of density and magnetic field within the active region. A dynamic range of up to 1500 (at 8.4 GHz) was achieved because these data were well suited to the self-calibration technique. The signatures of both optically thick gyroresonance emission are unambiguously identified, and magnetic fields and optically thin thermal free-free emission are outlined. Images are compared at 5 and 8.4 GHz in order to identify regions in the trailing part of the active region where optically thin four-harmonic gyroresonance emission is contributing to the observed brightness temperatures at 5 GHz, indicating the presence of 450 G fields. Title: Millimeter and hard X-ray/γ-ray observations of solar flares during the June 91 GRO campaign. Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J. Bibcode: 1992NASCP3137..502K Altcode: 1992como.work..502K We have carried out high-spatial-resolution millimeter observations of solar flares using the Berkeley-Illinois-Maryland Array (BIMA). At the present time, BIMA consists of only three elements, which is not adequate for mapping highly variable solar phenomena, but is excellent for studies of the temporal structure of flares at millimeter wavelengths at several different spatial scales. We present BIMA observations made during the Gamma Ray Observatories (GRO)/Solar Max 1991 campaign in Jun. 1991 when solar activity was unusually high. Our observations covered the period 8-9 Jun. 1991; this period overlapped the period 4-15 Jun. when the Compton Telescope made the Sun a target of opportunity because of the high level of solar activity. Title: Meter-decameter radio emission associated with a coronal mass ejection Authors: Kundu, M. R.; Gopalswamy, N. Bibcode: 1992LNP...399..268K Altcode: 1992esf..coll..268K; 1992LNP...399..268G; 1992IAUCo.133..268K A study of meter-dekameter radio emission associated with the 1986 Feb 10 coronal Mass ejection event is presented here. The event was accompanied by a major flare (optical importance 1B and X-ray importance C9.6), preceded by a filament disappearance. Changes in the intensity of a pre-existing noise storm was observed during the onset of the flare. A flare continuum, a moving type IV, and a type II occurred during the event. The event was also associated with a strong hard X-ray burst. The speeds of moving type IV burst and CME were of the same order of 1600 kms -1, while the type II shock speed was 1900 kms -1. The positional data indicate that the moving type IV burst and the inferred type II shock had different trajectories. The moving type IV burst was confined to one leg of the CME while the type II shock was far ahead of the CME leading edge. We discuss the inferred relation among different entities such as the CME, type II shock, type IV plasmoid and the erupting filament. Title: A 5 GHz Survey of Weak-Lined T Tauri Stars Authors: White, S. M.; Pallavicini, R.; Kundu, M. R. Bibcode: 1992ASPC...26..334W Altcode: 1992csss....7..334W No abstract at ADS Title: Multifrequency Observations of a Remarkable Solar Radio Burst Authors: White, S. M.; Kundu, M. R.; Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Kucera, T.; Bieging, J. H. Bibcode: 1992ApJ...384..656W Altcode: Observations of an impulsive solar-radio burst from three observatories are presented. The striking observational aspects of this flare are that the time profile was identical throughout at 8.6, 15, and 86 GHz, that the spectrum was apparently flat from 15 to 86 GHz, and that there was a sharp cutoff in the spectrum between 5.0 and 8.6 GHz. The simplest interpretation of the cutoff, namely as a plasma frequency effect, leads to the conclusion that there was exceptionally high-density material in the solar corona (of about 5 x 10 exp 11/cu cm). Very Large Array images at 15 GHz show a single-loop structure which brightened uniformly and showed little change in size during the whole impulsive phase. The flat spectrum is consistent with optically thin thermal bremsstrahlung emission, but the lack of observed soft X-ray emission and other properties of the flare cannot easily be accommodated by this mechanism. The possibility is explored that the emission is optically thick due to thermal absorption of nonthermal gyrosynchrotron emission, or optically thin gyrosynchrotron emission absorbed by high-density material intervening along the line of sight. Both of these explanations also face difficulties. Title: Radio observations of weak-lined T Tauri stars. Authors: White, S. M.; Pallavicini, R.; Kundu, M. R. Bibcode: 1992MmSAI..63..751W Altcode: We report the results of a search for radio-continuum emission from weak-lined T Tauri stars selected on the basis of a range of criteria. A correlation is found with strong X-ray emission and with youth. All the stars in the survey older than about 20 million years were not detected as radio sources. A flare was seen on one of the survey targets, with a rise time of several hours. Circular polarization was also seen in two of the targets, providing the first direct confirmation of the presence of magnetic fields on these stars. Title: Radio observations of solar and stellar coronae Authors: Kundu, M. R.; White, S. M. Bibcode: 1992MmSAI..63..715K Altcode: Recent results of radio observations of the solar and stellar coronae are reviewed. Attention is given to the results obtained on quiet-sun fine structures; the active region observations, with particular consideration given to the soft X-ray and radio comparisons of observations made during the Coronal Magnetic Structures Observing Campaign and the strength of the magnetic fields in the corona; the radio observations of solar flares; and the radio observations of stellar coronae of the RS Canum Venaticorum binaries, M dwarf stars, pre-main-sequence stars, and chemically-peculiar B stars. Also discussed are current issues in stellar radiophysics and perspectives in solar radio physics. Title: HST Observations of the Flare Star AU MIC Authors: Robinson, R. D.; Shore, S. N.; Carpenter, K. G.; Woodgate, B. E.; Maran, S. P.; Brandt, J. C.; Kundu, M. R.; White, S. M.; Linsky, J. L.; Walter, F. M. Bibcode: 1992ASPC...26...31R Altcode: 1992csss....7...31R No abstract at ADS Title: Largescale Structures Associated with Eruptive Flares and Radio Waves Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1992LNP...399..207G Altcode: 1992esf..coll..207G; 1992IAUCo.133..207G We review some recent results obtained from 2-dimensional imaging observations of the Sun using the Clark Lake multifrequency radioheliograph. The radioheliograph produced images of the Sun's corona on a daily basis at several frequencies within the range 20-125 MHz during the period 1982-87. Using these images both large scale structures as well as transient phenomena such as bursts have been studied. In this paper we discuss the nature of radio emission associated with eruptive filaments and CMEs. It is possible to trace the structure of magnetic fields in the corona based on the multifrequency observations of moving type IV bursts at meter and decameter wavelengths. We illustrate this by discussing specific events. We discuss a rare case of the detection of thermal radio emission in association with a fast CME. We estimate the CME mass using spatially resolved radio data. Title: VLA observations of solar active regions at 6 and 20 CM Authors: Alissandrakis, C. E.; Kundu, M. R.; Shevgaonkar, K. R. Bibcode: 1991A&A...251..276A Altcode: High-resolution observations are presented of two active regions at 6 and 20 cm over a period of 5 days, together with H-alpha and photospheric magnetic fields. The large-scale emission at 20 cm is associated with the H-alpha plage. In one region the strongest source was over the neutral line, near the tip of an active-region filament, which indicates that the emission probably originated in small-scale coronal loops. In the second region the peak of the emission was near a well-developed sunspot. Neither region showed evidence of large-scale loops joining their preceding and following parts. Several other sources were observed at 20 cm; a source associated with an H-alpha plage region crossed by a filament and one associated with a small bipolar region are briefly discussed. The 6-cm emission from a well-developed spot showed clearly the characteristics expected from gyroresonance model computations. Title: An Investigation of the Flare Star AU Mic with the Goddard High Resolution Spectrograph on the Hubble Space Telescope Authors: Maran, S. P.; Woodgate, B. E.; Carpenter, K. G.; Robinson, R. D.; Shore, S. N.; Linsky, J. L.; Brown, A.; Byrne, P. B.; Kundu, M. R.; White, S.; Brandt, J. C.; Shine, R. A.; Walter, F. M. Bibcode: 1991BAAS...23.1382M Altcode: No abstract at ADS Title: Large-Scale Features of the Sun at 20 Centimeter Wavelength Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R. Bibcode: 1991ApJ...379..366G Altcode: Results are reported from an experimental study of the characteristics of large-scale coronal structures such as active regions, plages, filaments, and coronal holes using data obtained with the VLA at 1.5 GHz during the period September 11-17, 1988. The radio data were supplemented with He 10830- A, H-alpha, and Calcium-K spectroheliograms. A statistical analysis of some of the characteristics of the active regions is performed. Most of the active region sources were found to be about 100 arcsec in size, with bridges between regions common; lower brightness temperature regions showed a higher degree of polarization in general. The maximum polarization was found at the edge of active regions but well within the associated plages. The degree of polarization from bright active regions was small (not more than 20 percent), in agreement with previous results. Evidence was found for compression of preexisting flux by the emerging flux from a new region, which took place in the apparent absence of magnetic reconnection. Title: Time Resolved Observations of the Lyman-Alpha Region in AU Mic with the Goddard High Resolution Spectrograph Authors: Woodgate, B. E.; Maran, S. P.; Carpenter, K. G.; Robinson, R. D.; Shore, S. N.; Linsky, J. L.; Byrne, P. B.; Kundu, M. R. Bibcode: 1991BAAS...23.1383W Altcode: No abstract at ADS Title: VLA Observations of Interacting Flaring Loops Authors: Kundu, M. R.; White, S. M.; McConnell, D. M. Bibcode: 1991SoPh..134..315K Altcode: We present 4.9 GHz observations of an impulsive radio burst observed at the Very Large Array on 1981 May 16. The flare occurred in a complex active region containing several spots. The radio burst lay at the edge of an active-region microwave source, close to a neutral line. The compact burst showed morphological evidence for the presence of two loops in the rise phase, with the subsequent burst peak lying between these loops. This suggests that interaction between the loops played some role in the initiation of the flare. The flare spectrum is consistent with thermal gyrosynchrotron emission. The main microwave peak was displaced from the nearest Hα kernels by about 10″, but there is strong evidence for post-flare loops coincident with the Hα kernels during the later stages of the event. Title: Coronal Magnetic Structures Observing Campaign. I. Simultaneous Microwave and Soft X-Ray Observations of Active Regions at the Solar Limb Authors: Nitta, N.; White, S. M.; Kundu, M. R.; Gopalswamy, N.; Holman, G. D.; Brosius, J. W.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T. Bibcode: 1991ApJ...374..374N Altcode: Using simultaneous microwave and soft X-ray measurements made with the Very Large Array (VLA) at 6 and 20 cm and the X-ray Polychromator (XRP) aboard the Solar Maximum Mission (SMM), we have studied two active regions near the solar limb. These observations were taken as part of the Coronal Magnetic Structures Observing Campaign (CoMStOC), a collaboration designed to study the magnetic field in the solar corona. The images in soft X-rays and at 20 cm wavelength are similar: both show peaks above the active regions and extended bridge of emission 200,000 km long connecting the two regions. The brightness temperature of the 20 cm emission is lower than that predicted from the X-ray emitting material, however; it can be attributed to free-free emission in cooler (<106 K) plasma not visible to XRP, with an optical depth ∼1. The 6 cm emission is concentrated at lower altitudes and in a ∼160,000 km long bundle of loops in the northern active region. Comparison of the 6 cm map with the potential magnetic field lines computed from photospheric magnetic fields (measured 2 days earlier) indicates that the 6 cm emission is associated with fields of less than ∼200 G. Such fields would be too weak to attribute the observed 6 cm emission to gyroresonance radiation. Analysis of the 6 cm loop bundle indicates that it is strongly asymmetric, with the magnetic field in the northern leg ∼2 times stronger than in the southern leg; the 6 cm emission most likely arises from a combination of hot ( ≥ 2 × 106 K) and cool plasmas, while the 20 cm emission becomes optically thick in the cooler (∼9 × 103 K) plasma. We estimate an Alfvén speed ∼7000 km s-1 and ratio of electron gyrofrequency to plasma frequency ∼1.0 in the northern leg of the 6 cm loop. Title: A Search for Solar Oscillations in the Solar Chromosphere Using Millimeter Interferometric Observations Authors: Kundu, M. R.; White, S. M. Bibcode: 1991BAAS...23R1033K Altcode: No abstract at ADS Title: Global Streamer Evolution Authors: Thejappa, G.; Kundu, M. R.; Gopalswamy, N. Bibcode: 1991BAAS...23.1045T Altcode: No abstract at ADS Title: On the Reconciliation of Simultaneous Microwave Imaging and Hard X-Ray Observations of a Solar Flare Authors: Nitta, N.; White, S. M.; Schmahl, E. J.; Kundu, M. R. Bibcode: 1991SoPh..132..125N Altcode: We have compared microwave imaging data for a small flare with simultaneous hard X-ray spectral observations. The X-ray data suggest that the power-law index δ of the energy distribution of the radiating electrons is 5.3 (thick-target) which differs significantly from the estimate (δ = 1.4) from a homogeneous optically-thin gyrosynchrotron model which fits the radio observations well. In order to reconcile these results, we explore a number of options. We investigate a double power-law energy spectrum for the energetic electrons in the flare, as assumed by other authors: the power law is steep at low energies and much flatter at the higher energies which produce the bulk of the microwaves. The deduced break energy is about 230 keV if we tentatively ignore the X-ray emission from the radio-emitting electrons: however, the emission of soft photons by the flat tail strongly contributes to the observed hard X-ray range and would flatten the spectrum there. A thin-target model for the X-ray emission is also inconsistent with radio data. An inhomogeneous gyrosynchrotron model with a number of free parameters and containing an electron distribution given by the thick-target X-ray model could be made to fit the radio data. Title: VLA Observations of Radio Filaments Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R. Bibcode: 1991BAAS...23.1045G Altcode: No abstract at ADS Title: New Observations of Solar Noise Storm Radiation at Decameter Wavelengths Authors: Thejappa, G.; Kundu, M. R. Bibcode: 1991SoPh..132..155T Altcode: We report multifrequency observations of storm continuum and other radio bursts. Based on their positional study and their correlation with other coronal and photospheric features, we deduce that the storm source is located in the magnetic field lines lying above a single bipolar active region. Energetic electrons trapped in the magnetic structures above the spots must be responsible for the storm radiation. We show that spontaneous emission of Langmuir waves by anisotropic distributions can explain both storm continuum and bursts self-consistently. Whenever the collisional damping (νc) is more than the growth (- υA), there is a steady emission responsible for the continuum, and whenever νc = -υA (which may be satisfied randomly) there is a sudden jump in Tb giving rise to bursts. The number density of energetic particles required to explain the storm continuum at 73.8, 50, and 30.9 MHz frequencies is estimated to lie in the limits nb/ne ∼ 10−10−10−9 in the context of the present observations. The brightness spectrum of the storm continuum is computed and compared with observations. Title: Multifrequency Observations of a Remarkable Solar Radio Burst Authors: White, S. M.; Kundu, M. R.; Bastian, T. S.; Gary, D. E.; Hurford, G. J.; Kucera, T.; Bieging, J. H. Bibcode: 1991BAAS...23.1043W Altcode: No abstract at ADS Title: Millimeter Imaging of Energetic Electrons in Solar Flares in Conjunction with GRO Experiments Authors: Kundu, M. R.; White, S. M. Bibcode: 1991BAAS...23Q1073K Altcode: No abstract at ADS Title: Millimeter Interferometric Observations of Solar Flares During the SOLAR-A Mission Authors: Kundu, M. R.; White, S. M. Bibcode: 1991LNP...387..338K Altcode: 1991fpsa.conf..338K We present the results of the first high-spatial-resolution interferometric observations of solar flares at millimeter wavelengths, carried out with the Berkeley-Illinois-Maryland Array (BIMA). The observations represent an improvement of an order of magnitude in both sensitivity and spatial resolution compared with previous solar observations at these wavelengths. Most of the flares occurring within the field of view during the observations have been detected by BIMA, including both very impulsive and longer-duration events. It appears that millimeter burst sources are not much smaller than microwave sources. If the emission in the flash phase is predominantly due to gyrosynchrotron emission, we can rule out thermal gyrosynchrotron models for the radio emission because the flux at millimeter wavelengths is too high. During the Solar-A mission we plan to obtain both imaging data as well as dedicated patrol observations of flare time profiles at millimeter wavelengths. Title: Strong Magnetic Fields and Inhomogeneity in the Solar Corona Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N. Bibcode: 1991ApJ...366L..43W Altcode: It is shown that fields of 1800 G can exist in the corona based on observations of gyroresonance emission at 15 GHz at coronal temperatures. The strong fields occur in a small source radiating in the extraordinary (x) mode over the penumbra of a large symmetric sunspot. The optically-thin ordinary mode emission from the region shows a nearby peak at only 36,000 K which may be due to a sunspot plume, and a hole over the umbra consistent with the expected low-density material there. The x-mode source is highly asymmetric, despite the apparent symmetry of the sunspot, and its appearance and location imply that the strongest magnetic fields in the corona are localized in a compact flux tube. Title: High spatial resolution observations of solar flares at 3.3 mm wavelength Authors: Kundu, M. R.; White, S. M.; Welch, W. J.; Bieging, J. H. Bibcode: 1991AdSpR..11e..91K Altcode: 1991AdSpR..11...91K We present the first high-spatial-resolution interferometric observations of solar flares at millimeter wavelengths, carried out with the Berkeley-Illinois-Maryland Array (BIMA). The observations represent an improvement of an order of magnitude in both sensitivity and spatial resolution compared with previous solar observations at these wavelengths. Most of the flares occurring within the field of view during the observations were detected by BIMA, including both very impulsive and longer-duration events. It appears that millimeter burst sources are not much smaller than microwave sources. If the emission in the flash phase is predominantly due to gyrosynchrotron emission, we can rule out thermal gyrosynchrotron models for the radio emission because the flux at millimeter wavelengths is too high. During the Flares 22 campaign we will collect both imaging data as well as dedicated patrol observations of flare time profiles at millimeter wavelengths. Title: Millimeter Solar Observing with BIMA Authors: Kundu, M. R.; White, S. M.; Welch, W. J. Bibcode: 1991max..conf...11K Altcode: No abstract at ADS Title: VLA Observations of Active Region 5555 During the 1st Max'91 Campaign Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R. Bibcode: 1991max..conf...23S Altcode: No abstract at ADS Title: Association of a Type IV Burst with a Slow CME Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1991max..conf..139G Altcode: No abstract at ADS Title: Triennial Report of IAU Commission 40 (Radio Astronomy) 1988-1991 Authors: Altenhoff, Wilhelm J.; Andernach, Heinz; Baars, Jaap; Chini, Rolf; Cohen, R. J.; Condon, J. J.; Fukui, Y.; Güsten, R.; van der Hulst, J. M.; Henkel, C.; Huchtmeier, W.; Ishiguro, M.; Krichbaum, T.; Kundu, M.; Lasenby, A.; Reich, W.; Roelfsema, P.; Thorsett, S. E.; Tuffs, R.; Walmsley, C. M.; Wendker, H.; Wielebinski, R.; Wilson, T. L.; Witzel, A. Bibcode: 1991IAUTA..21..449A Altcode: No abstract at ADS Title: Meter-Decameter Observations of Dme Flare Stars with the Clark-Lake Radio Telescope Authors: Jackson, P. D.; Kundu, M. R.; Kassim, N. Bibcode: 1990SoPh..130..391J Altcode: The now-closed Clark Radio Observatory was used in 1984 and 1985 to search for flaring emission from a number of dMe flare stars in the 30.9 to 110.6 MHz frequency range. No emission was found to greatly exceed detection limits which range from about 1 Jy for 1 hr averaging, to about 50 Jy for 1 s averaging, even though flares were often seen to tens of mJy at 20 cm using the VLA for those times when VLA-CLRO observations were coordinated. There are marginal detections of flaring from AD Leo over two periods on December 15, 1985 which mark the beginning and the end of along-lasting, narrow-band flare at 1415 MHz. Title: Coronal mass ejections and solar radio bursts Authors: Kundu, Mukul R. Bibcode: 1990IJRSP..19..506K Altcode: The radio signatures and properties of coronal mass ejection (CME) events are discussed. The signatures are mostly in the form of type 2 and type 4 burst emissions. Although type 2 bursts are temporally associated with CMEs, it is shown that there is no spatial relationship between them. It is shown that moving type 4 and type 2 bursts can be associated with slow CMEs with speeds as low as 200 km/s, contrary to the previous belief that only CMEs with speeds greater than 400 km/s are associated with radio bursts. A specific event is discussed in which the CME and type 4 burst had nearly the same speed and direction, but the type 2 burst location was behind the CME and its motion was transverse. The speed and motion of the type 2 burst strongly suggest that the type 2 shock was decoupled from the CME and probably due to a flare behind the limb. Therefore only the type 4 source could be directly associated with the slow CME. Title: The Observation of an Unusually Fast Type IV Plasmoid Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1990ApJ...365L..31G Altcode: A moving type IV burst of the 'isolated source' type has been detected whose out-of-plane speed, at 1600 km/sec, becomes about 2800 km/sec upon assumption of radial motion; this is twice as high as previously reported speeds for bursts of this type. While shock waves are known to have such high speeds, and a shock wave is likely to form ahead of a high-speed plasmoid, no radio signature has been observed for such a shock. This lack of shock detection may, however, be primarily due to poor observing conditions. Energetic electrons, trapped in an about 1.4 G magnetic field of the plasmoid, can adequately account for the emission. Title: Book-Review - Energetic Phenomena on the Sun Authors: Kundu, M. R.; Woodgate, B.; Schmahl, E. J.; Staude, J. Bibcode: 1990AN....311..416K Altcode: No abstract at ADS Title: UVSP and VLA observations of the 24 June 1980 flare: Asymmetric or isotropic beaming? Authors: Kundu, M. R.; Cheng, C. C.; Schmahl, E. J. Bibcode: 1990SoPh..129..343K Altcode: Observations of the 15:22 UT flare of 24 June 1980 were made using the Very Large Array (VLA) at 6 cm wavelength simultaneously with the Hard X-ray Imaging Spectrometer (HXIS) aboard the Solar Maximum Mission. It was found that at the peak of the impulsive phase, the brightest microwave point appeared to lie between the soft (3.6-8.0 keV) and hard (22-30 keV) X-ray maxima, which were themselves separated by ∼ 20″ (Kundu et al., 1984). Since the publication of these results, we have analyzed the imaging data from the Ultraviolet Spectrometer Polarimeter (UVSP) with the goal of narrowing the possible interpretations of the event. Like the VLA and HXIS, the UVSP observations provide information about the location of the primary electrons; the observations taken together suggest that the fast electrons were symmetrically distributed within the flare loop. Title: Filament Eruption and Storm Radiation at Meter / Decameter Wavelengths Authors: Kundu, M. R.; Gopalswamy, N. Bibcode: 1990SoPh..129..133K Altcode: We report the study of a weak noise storm observed by the Clark Lake multifrequency radioheliograph at four frequencies. The noise storm onset was associated with a filament eruption and a gradual rise and fall in soft X-rays. We compare the noise storm emission with related emissions in other wavelengths to develop a composite scenario of the event. Using the properties of the quiet corona inferred from the simultaneously observed quiet-Sun radiation, we estimate the brightness temperature of the storm continuum, which seems to be consistent with the observations reported in Solar Geophysical Data. Superthermal particles with a temperature that is ten times the coronal electron temperature and a density of ∼ 10−3 times the coronal density are adequate to explain the observed radiation. Since the noise storm observations were made at four frequencies, we were able to obtain a brightness temperature spectrum of the storm radiation. If the storm radiation is affected in the same way as the quiet-Sun emission by inhomogeneities, the observed spectrum can be interpreted as due to propagation effects. Since the Clark Lake instrument can observe both quiet Sun and weak bursts simultaneously, we were able to estimate the propagation effects from the quiet-Sun observations and use it to correct the brightness temperature of storm radiation. Title: Multiple Moving Magnetic Structures in the Solar Corona Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1990SoPh..128..377G Altcode: 1990IAUCo.121P.377G We report the study of moving magnetic structures inferred from the observations of a moving type IV event with multiple sources. The ejection contains at least two moving radio emitting loops with different relative inclinations. The radio loops are located above multiple Hα flare loops in an active region near the limb. We investigate the relationship between the two systems of loops. The spatial, temporal and geometrical associations between the radio emission and near surface activities suggest a scenario similar to coronal mass ejection (CME) events, although no CME observations exist for the present event. From the observed characteristics, we find that the radio emission can be interpreted as Razin suppressed optically thin gyrosynchrotron emission from nonthermal particles of energy ∼ 100, keV and density ∼ 102-105 cm−3 in a magnetic field ≤ 2 G. Title: Microwave and X-Ray Observations of a Major Confined Solar Flare Authors: Schmahl, E. J.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.; Kundu, M. R. Bibcode: 1990ApJ...358..654S Altcode: Observations of an X4 flare of May 19, 1984 using the VLA and the SMM X-ray Polychromator are discussed. The 6 cm radio source remained stationary throughout the decay phase. Combined with other evidence, this indicates that the flare was magnetically confined and did not disrupt the complex structure of its region. The observed structures may be associated with a neutral sheet connecting the two bipoles. Title: First High Spatial Resolution Interferometric Observations of Solar Flares at Millimeter Wavelengths Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Bieging, J. H.; Hurford, G. J. Bibcode: 1990ApJ...358L..69K Altcode: The first high spatial resolution interferometric observations of solar flares at millimeter wavelengths, carried out with the Berkeley-Illinois-Maryland Array are presented. The observations were made at 3.3 mm wavelength during the very active periods of March 1989, using one or three baselines with fringe spacings of 2-5 arcsec. The observations represent an improvement of an order of magnitude in both sensitivity and spatial resolution compared with previous solar observations at these wavelengths. It appears that millimeter burst sources are not much smaller than microwave sources. The most intense bursts imply brightness temperatures of over 10 to the 6th K and are due to nonthermal gyrosynchrotron emission or possibly thermal free-free emission. If the emission in the flash phase is predominantly due to gyrosynchrotron emission, thermal gyrosynchrotron models can be ruled out for the radio emission because the flux at millimeter wavelengths is too high. Title: Microbursts at Meter-Decameter Wavelengths Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R. Bibcode: 1990SoPh..127..165T Altcode: We study the characteristics of microbursts using a large data base obtained with the multifrequency radioheliograph of the Clark Lake Radio Observatory. Most of the new observations were made during July 29, 1985 to August 2, 1985; we also include for statistical studies the microburst data used in our earlier studies. We perform a statistical analysis of many characteristics such as frequency drift, source size and brightness temperature and compare them with the properties of normal type III bursts. We investigate the coronal structures and surface activities associated with some of the events. We find that (i) the brightness temperature is in the range 6 × 105 K to 6 × 107 K; (ii) the drift rate of the microbursts is slightly smaller than that of normal type III bursts, implying electron beams with speeds ∼0.2c. Title: CoMStOCI: Physical Properties of an Active Region Loop Observed at the Solar Limb Authors: Holman, G. D.; Brosius, J. W.; Nitta, N.; White, S. M.; Kundu, M. R.; Gopalswamy, N.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T. Bibcode: 1990BAAS...22..899H Altcode: No abstract at ADS Title: Evolution of Active Regions at 20 cm Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R. Bibcode: 1990BAAS...22..795G Altcode: No abstract at ADS Title: Magnetic Field Strengths in Post-Flare Loop Systems Authors: Schmahl, E. J.; Kundu, M. R. Bibcode: 1990BAAS...22Q.827S Altcode: No abstract at ADS Title: The solar probe mission Authors: Feldman, W. C.; Anderson, J.; Bohlin, J. D.; Burlaga, L. F.; Farquhar, R.; Gloeckler, G.; Goldstein, B. E.; Harvey, J. W.; Holzer, T. E.; Jones, W. V.; Kellogg, P. J.; Krimigis, S. M.; Kundu, M. R.; Lazarus, A. J.; Mellott, M. M.; Parker, E. N.; Rosner, R.; Rottman, G. J.; Slavin, J. A.; Suess, S. T.; Tsurutani, B. T.; Woo, R. T.; Zwickl, R. D. Bibcode: 1990AIPC..203..101F Altcode: 1990pacr.rept..101F The Solar Probe will deliver a 133.5 kg science payload into a 4 Rs perihelion solar polar orbit (with the first perihelion passage in 2004) to explore in situ one of the last frontiers in the solar system-the solar corona. This mission is both affordable and technologically feasible. Using a payload of 12 (predominantly particles and fields) scientific experiments, it will be possible to answer many long-standing, fundamental problems concerning the structure and dynamics of the outer solar atmosphere, including the acceleration, storage, and transport of energetic particles near the Sun and in the inner (<65 Rs) heliosphere. Title: High-Dynamic-Range Multifrequency Radio Observations of a Solar Active Region Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N. Bibcode: 1990BAAS...22R.794W Altcode: No abstract at ADS Title: VLA Observations of Solar Active Regions at 6 and 20 cm During the Spacelab 2 Mission Authors: Alissandrakis, C. E.; Kundu, M. R.; Shevgaonkar, R. K. Bibcode: 1990BAAS...22..795A Altcode: No abstract at ADS Title: Millimeter-Interferometer Observations of Solar Flares Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Bieging, J. H.; Hurford, G. J. Bibcode: 1990BAAS...22..823K Altcode: No abstract at ADS Title: New Observations of Storm Radiation at Decameter Wavelengths and Their Interpretation Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R. Bibcode: 1990BAAS...22..794T Altcode: No abstract at ADS Title: Kilometric Shock-Associated Events and Microwave Bursts Authors: Kundu, M. R.; MacDowall, R. J.; Stone, R. G. Bibcode: 1990Ap&SS.165..101K Altcode: The peak times of impulsive microwave bursts are compared with those of shock-associated (SA) kilometric radio events. The first peaks in these two frequency regimes are usually well-correlated in time, but the last peaks of the SA events observed at 1 MHz occur an average of 20 min after the last impulsive microwave peaks. In some cases, the SA events overlap in time with the post-burst increases of microwave bursts; sometimes there is general correspondence in their intensity time profiles. These observations suggest that the earlier components of the SA events are usually caused by electrons accelerated in or near the microwave source region. We discuss the possibility that the later components of some SA events could be associated with nonthermal electrons responsible for microwave post-burst increases, although they have traditionally been attributed to electrons accelerated at type II burst producing shocks in the upper corona. Title: Magnetic field reconnection in solar and stellar flares Authors: Kundu, M. R.; White, S. M. Bibcode: 1990AdSpR..10i..85K Altcode: 1990AdSpR..10...85K Radio observations are sensitive to energetic electrons, and thus are an important tool for studying the properties of solar flares. High spatial resolution multifrequency observations at centimeter wavelengths can provide important information on the region of energy release during flares and, therefore, on their triggering mechanisms. The changes in polarization and its structure during the preflare and impulsive phase have led to inferences about magnetic field topology in the flaring region /1/. We have learnt that evolving magnetic field structures often trigger the flare /2/. In this paper, we discuss evidence for magnetic reconnection in both solar and stellar flares derived from radio observations. We present two cases of solar flares well-observed by the VLA which show interacting magnetic structures leading to a flare. Both cases are strongly suggestive of reconnection. In the second part of the paper we discuss more indirect evidence based on flares in the coronae of red dwarf stars. Title: Some Problems in Low Frequency Solar Radio Physics Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1990LNP...362...97G Altcode: 1990lfas.work...97G Several important problems in solar radio physics can be attacked using the high spatial resolution observations from a low frequency space array, as the problem of ionospheric refraction does not exist. Noise storms are believed to occur in closed magnetic loops due to trapped superthermal particles. Recent radioheliograph observations suggest such a magnetic field topology up to altitudes of about 40 MHz emission. The problem of relative locations and sources of the storm continuum and bursts can be effectively studied by imaging them with higher spatial resolution. Interplanetary type II bursts are observed from heights above ~ 10 R while coronal type II bursts are observed from heights less than ~ 3 R. Observations filling this gap have important implications for the understanding of solar-terrestrial relations through shocks and mass ejections. Title: Millimeter and Microwave Activity of the Sun Authors: Kundu, M. R.; White, S. M. Bibcode: 1990IAUS..142..457K Altcode: Preliminary results of high-spatial-resolution millimeter observations of recent solar flares carried out with the Berkeley-Illinois-Maryland Array are presented. Findings obtained from multifrequency observations using the VLA are reported. The time profiles of several bursts during March 1989 are presented. Most of the bursts were impulsive and short-lived, and a number of longer-duration bursts were observed as well. All the bursts were fairly weak, with none exceeding 1 sfu of correlated amplitude. A number had rise times less than the available resolution of 10 sec. VLA observations in September 1988 showed that there is exceptionally good correspondence between the 1.5-GHz radio sources and the regions which are dark in He 10830 images and bright in Ca images. Title: Microbursts at Meter-Decameter Wavelengths Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R. Bibcode: 1990IAUS..142..521T Altcode: No abstract at ADS Title: The Radio Spectra of Rs-Canum Stars Authors: White, S. M.; Kundu, M. R.; Uchida, Y.; Nitta, N. Bibcode: 1990ASPC....9..239W Altcode: 1990csss....6..239W The results of observations of several systems are presented for the 0.327-90 GHz range to study the radio coronae and outbursts associated with the RS CVn stars, as well as their visibility at millimeter wavelengths. The radio spectra are observed with the VLA and the Nobeyama 45-m millimeter-wavelength telescope. The three stars observed with the Nobeyama and VLA telescopes are UX Ari, AR Lac, and HR 5110, and the frequencies and conditions of the nonsimultaneous observations are set forth. Observations of the RS CVn systems at mm wavelengths is possible, and it is theorized that important information regarding flares and energy release can be derived from these data. A simple model is presented for the radio-coronae source related to outbursts of up to 5 GHz, and the onset of outbursts are predicted to be accompanied by low frequency type-II plasma emission. Title: The Sun at the Vla's Metric and Decimetric Wavelengths Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.; Schmahl, E. J. Bibcode: 1990IAUS..142..523W Altcode: Preliminary results of solar observations at 0.333 and 1.5 GHz made with the VLA during the September 11-17, 1988 period are presented. Generally, there are few structural changes in the active region sources from one day to the next, suggesting that structural evolution is relatively slow. Contour maps at 1.5 GHz are presented for each of the four days. Two noise storms were present at 0.33 GHz all week and were highly polarized. Title: Measurement of solar magnetic fields from radio observations Authors: Kundu, M. R. Bibcode: 1990MmSAI..61..431K Altcode: Measurements of magnetic fields in the sun's atmosphere using radio observations are discussed. Radio measurements of magnetic fields in the chromosphere and the corona are indirect. In the chromosphere, these are based upon the measurement of polarization of active regions at millimeter wavelengths. In the transition region and the corona, the properties of gyroresonance radiation of active regions at centimeter wavelengths are used. Total intensity and polarization maps and modeling are used to determine which harmonic (second or third) is predominant in the active region emission. A direct method of measuring coronal magnetic fields using cyclotron line emission is discussed, and the relevant data as presently available are presented. Title: Dual Frequency Variability Study of an Active Region Authors: Shevgaonkar, R. K.; Kundu, M. R. Bibcode: 1990IAUS..142..489S Altcode: The VLA is used to investigate a short-time variability of a solar region at 6 and 2 cm wavelengths simultaneously. The observed low brightness temperatures indicate that the emission is mainly originating from the chromosphere-corona transition region. It is shown that an independent variation of a few percent in the magnetic field (900 +/- 45 G) and a factor-of-two variation in the density (2 to 4 x 10 exp 10/cu cm) over a time scale of a few hours is required to explain the uncorrelated brightness temperature at the two wavelengths. Title: The Radio Signatures of a Slow Coronal Mass Ejection: Electron Acceleration at Slow-Mode Shocks? Authors: Kundu, M.; Gopalswamy, N.; White, S.; Cargill, P.; Schmahl, E. J.; Hildner, E. Bibcode: 1989ApJ...347..505K Altcode: The evolution of a coronal mass ejection (CME) event observed on February 17, 1985 is studied using two-dimensional radio imaging observations along with simultaneously obtained coronagraph observations. This event shows that a slow CME can be associated with type II and type IV radio bursts. The implications of the spatial association of the radio bursts with the CME are discussed. It is argued that the CME is due to an instability of the large-scale magnetic field in a helmet streamer and that the radio bursts are some of the responses to this instability. The new feature of this event is the clear association of the moving type IV burst with a CME traveling slower than the coronal Alfven speed. The structure of slow shocks driven by such a CME is discussed, and it is shown that shock drift and diffusive acceleration are ineffective. An acceleration mechanism involving current-driven lower hybrid waves is proposed. Title: A VLA Survey of Nearby Flare Stars Authors: White, Stephen M.; Jackson, Peter D.; Kundu, Mukul R. Bibcode: 1989ApJS...71..895W Altcode: Results from a VLA survey of nearby flare stars are combined with those of other surveys to compare the incidence of radio detection of late-type dwarf stars with other stellar parameters. About 40 percent of known nearby flare stars were detected in the survey. It is found that there is a deficiency of radio detections for M dwarf stars later than dM5.5, in agreement with the falloff in X-ray luminosity of these stars. Evidence is found for a link between radio activity and rotation, because most of the detected sources are stars which are believed to be young disk stars and are still rapid rotators. Title: Simple non-thermal models for the quiescent radio emission of dMe flare stars. Authors: White, S. M.; Kundu, M. R.; Jackson, P. D. Bibcode: 1989A&A...225..112W Altcode: Simple nonthermal gyrosynchrotron models were applied to the quiescent emission of M dwarf stars. Evidence is presented which suggests that these stars have a number of smaller active regions contributing to the observed flux. The evidence includes an absence of Zeeman polarization in optical observations and a lack of polarization in quiescent emission. Title: Soft X-Ray, Microwave, and Hard X-Ray Emission from a Solar Flare: Implications for Electron Heating and Acceleration in Current Channels Authors: Holman, Gordon D.; Kundu, Mukul R.; Kane, Sharad R. Bibcode: 1989ApJ...345.1050H Altcode: The soft X-ray, microwave, and hard X-ray emissions from the solar flare of May 14, 1980 are studied. The flare consists of a gradual component in soft X-rays and microwaves and a superposed impulsive burst accompanied by hard X-ray emission. The impulsive phase of the flare appears in the soft X-ray emission as a temperature spike and as an increased rate of energy dissipation into the plasma. A new, spatially and spectrally distinct, microwave component appears during the impulsive burst. The data are interpreted in terms of Joule heating and the electric field acceleration of electrons in one or more current sheets. It is found that all three emissions can be generated with sub-Dreicer electric fields. The soft X-ray emitting plasma can be heated by a single current sheet only if the resistivity in the sheet is well above the classical, collisional resistivity. Conditions are also given for the hard X-ray emission to be from nonthermal electrons with classical resistivity. Title: Evidence for Noise Storm Emission by Superthermal Particles During a Filament Eruption Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1989BAAS...21.1146G Altcode: No abstract at ADS Title: Radio Observations of Coronal Changes Authors: Kundu, M. R.; Gopalswamy, N. Bibcode: 1989BAAS...21.1145K Altcode: No abstract at ADS Title: Limb Passage of a Microwave Source Authors: Schmahl, E. J.; Kundu, M. R. Bibcode: 1989BAAS...21R1145S Altcode: No abstract at ADS Title: Microbursts at Meter-Decameter Wavelengths Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R. Bibcode: 1989BAAS...21.1145T Altcode: No abstract at ADS Title: Time Variability of Solar Active Regions at Centimeter Wavelengths Authors: Shevgaonkar, R. K.; Kundu, M. R. Bibcode: 1989ApJ...342..586S Altcode: An analysis is presented of the variability of centimeter wavelength emission originating from the solar transition region and lower corona, and the variability is compared with the sun's quiescent emission. Sequential dual wavelength observations are presented and used to put constraints on a possible model of the variability of active region emissions and to better understand the dynamics of active regions. It is shown that gyroresonance emission contributes significantly to the active region emission at 6 cm, whereas all the quiet-sun emission can be attributed to free-free emission. From comparison of the quiet-sun and active region models, it is shown that the density at the base of the transition region is higher in active regions. Title: Energetic Phenomena on the Sun Authors: Kundu, Mukul R.; Woodgate, B.; Schmahl, E. J. Bibcode: 1989ASSL..153.....K Altcode: 1989eps..conf.....K No abstract at ADS Title: The First Interferometric Observations with Arc-Second Resolution of Solar Radio Bursts at Millimeter Wavelengths Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Bieging, J. H. Bibcode: 1989BAAS...21..861K Altcode: No abstract at ADS Title: VLA Observations of a Small Impulsive Flare Authors: White, S. M.; Kundu, M. R.; McConnell, D. Bibcode: 1989BAAS...21R.834W Altcode: No abstract at ADS Title: Meter Wave Radio Signatures of Slow CME's and Coronal Streamer Evolution Authors: Kundu, M. R.; Gopalswamy, N. Bibcode: 1989BAAS...21R.857K Altcode: No abstract at ADS Title: Partially Occulted Microwave and X-ray Flares Authors: Schmahl, E. J.; Kundu, M. R.; Tappin, J.; Simnett, G. Bibcode: 1989BAAS...21Q.834S Altcode: No abstract at ADS Title: Radioheliograph and White-Light Coronagraph Studies of a Coronal Mass Ejection Event Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1989SoPh..122..145G Altcode: We analyze the radioheliograph and SMM-C/P observations of 1986 November 3 mass ejection event. The metric radio emissions are the only detected activity associated with the mass ejection, but are adequate to study the evolution of the event. The start time of the ejection seems to precede a possible flare behind the limb indicated by the early type III bursts. We discuss the physical relation between various types of bursts and the CME. We interpret moving type IV bursts as a plasma emission process. It is also shown using white-light coronagraph data that the density in the source region of the moving type IV is sufficient to support second harmonic plasma emission at the observed frequency of 50 MHz. Title: Interpretation of Multiwavelength Observations of Solar Active Regions Obtained During CoMStOC Authors: Brosius, J. W.; Holman, G. D.; Nitta, N.; White, S. M.; Kundu, M. R.; Gopalswamy, N.; Schmelz, J. T.; Saba, J. R. L.; Willson, R. Bibcode: 1989BAAS...21..838B Altcode: No abstract at ADS Title: Radio and Optical Observations of Moving Magnetic Structures in the Solar Corona Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1989BAAS...21..857G Altcode: No abstract at ADS Title: Simultaneous Microwave and Soft X-ray Observations of Active Regions at the Solar Limb Authors: Nitta, N.; White, S.; Kundu, M.; Gopalswamy, N.; Holman, G.; Brosius, J.; Schmelz, J.; Saba, J.; Strong, K. Bibcode: 1989BAAS...21..828N Altcode: No abstract at ADS Title: Joule Heating and Runaway Electron Acceleration in a Solar Flare Authors: Holman, G. D.; Kundu, M. R.; Kane, S. Bibcode: 1989BAAS...21..864H Altcode: No abstract at ADS Title: The Sun at the VLA's Meter and Decimeter Wavelengths Authors: White, S. M.; Gopalswamy, N.; Kundu, M. R. Bibcode: 1989BAAS...21..861W Altcode: No abstract at ADS Title: Simultaneous Multi-Frequency Imaging Observations of Solar Microwave Bursts Authors: Kundu, M. R.; White, S. M.; Schmahl, E. J. Bibcode: 1989SoPh..121..153K Altcode: 1989IAUCo.104..153K We review the results of simultaneous two-frequency imaging observations of solar microwave bursts with the Very Large Array. Simultaneous 2 and 6 cm observations have been made of bursts which are optically thin at both frequencies, or optically thick at the lower frequency. In the latter case the source structure may differ at the two frequencies, but the two sources usually seem to be related. However, this is not always true of simultaneous 6 and 20 cm observations. The results have implications for the analysis of non-imaging radio data of solar and stellar flares. Title: A Slowly Moving Plasmoid Associated with a Filament Eruption Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1989SoPh..122...91G Altcode: We report the imaging observations of a slowly moving type IV burst associated with a filament eruption. This event was preceded by weak type III burst activity and was accompanied by a quasi-stationary continuum that persisted for several hours. The starting times and speeds of moving type IV burst and the erupting filament are nearly the same, implying a close physical relation between the two. The moving type IV burst is interpreted as gyrosynchrotron emission from a plasmoid containing a magnetic field of ∼1-2 G and nonthermal electrons of density ∼105-106 cm−3 with a relatively low average energy of ∼50 keV. Title: Quiscent and flaring radio emission from the flare stars AD Leonis, EQ Pegasi, UV Ceti, Wolf 630, YY Geminorum and YZ Canis Minoris. Authors: Jackson, P. D.; Kundu, M. R.; White, S. M. Bibcode: 1989A&A...210..284J Altcode: Observations of the flare stars AD Leo, EQ Peg, UV Cet, Wolf 630, YY Gem, and YZ CMi at 6 and 20 cm wavelengths are presented. These observations display how a sample of the more active radio flare stars behave over periods of several hours. An extensive time analysis at five minute resolution, to investigate the typical variability of these stars, is presented together with a ten-second-resolution time analysis for periods of enhanced activity. Highlights are the enhanced 6-cm activity from both components of the UV Ceti system, quiescent emission from UV Ceti at 20 cm (which has a higher flux than the quiescent emission at 6 cm), the possible detection of polarized quiescent emission, a 20-cm flare from AD Leo in which the polarization changes sign during the rise phase of the flare, and a relatively high level of 6-cm emission from AD Leo. Title: Recent results of meter-decameter wave observations of solar flares. Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1989sasf.confP.185G Altcode: 1989IAUCo.104P.185G; 1988sasf.conf..185G The authors present recent results from meter-decameter imaging of several classes of solar radio bursts: preflare activity in the form of type III bursts, correlated type IIIs from distant sources, and type II and moving type IV bursts associated with flares and CMEs. Title: Non-thermal electrons and stellar radio emission. Authors: White, S. M.; Kundu, M. R. Bibcode: 1989sasf.confP..37W Altcode: 1989IAUCo.104P..37W Radio emission from dMe flare stars has both a flaring and a quiescent component. When one compares stellar radio emission with the Sun, however, one finds that the apparent brightness temperature of the quiescent component often exceeds the temperature of non-thermal solar radio flares, and so it is likely that stellar quiescent emission also comes from non-thermal electrons. Here the authors briefly review the observations of quiescent emission, argue that the emitting regions are small, show that such small regions can still account for the observed fluxes, and discuss the source of electrons. Title: Joule heating and runaway electron acceleration in a solar flare Authors: Holman, Gordon D.; Kundu, Mukul R.; Kane, Sharad R. Bibcode: 1989dots.work..198H Altcode: The hard and soft x ray and microwave emissions from a solar flare (May 14, 1980) were analyzed and interpreted in terms of Joule heating and runaway electron acceleration in one or more current sheets. It is found that all three emissions can be generated with sub-Dreicer electric fields. The soft x ray emitting plasma can only be heated by a single current sheet if the resistivity in the sheet is well above the classical, collisional resistivity of 107 K, 1011/cu cm plasma. If the hard x ray emission is from thermal electrons, anomalous resistivity or densities exceeding 3 x 1012/cu cm are required. If the hard x ray emission is from nonthermal electrons, the emissions can be produced with classical resistivity in the current sheets if the heating rate is approximately 4 times greater than that deduced from the soft x ray data (with a density of 1010/cu cm in the soft x ray emitting region), if there are at least 104 current sheets, and if the plasma properties in the sheets are characteristic of the superhot plasma observed in some flares by Lin et al., and with Hinotori. Most of the released energy goes directly into bulk heating, rather than accelerated particles. Title: Energetic phenomena on the Sun: Introduction. Authors: Kundu, M. R.; Woodgate, B. Bibcode: 1989epos.conf.....K Altcode: Contents: 1. Previous history. 2. The Solar Maximum Mission: objectives, instruments, operations. 3. Summary of workshop results. Title: Particle acceleration. Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.; Alissandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.; Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.; Tsuneta, S.; van Hoven, G. Bibcode: 1989epos.conf..127V Altcode: Contents: 1. Introduction. 2. Phenomena associated with mildly-relativistic electrons. 3. Phenomena associated with ions and relativistic electrons in solar flares. 4. Theoretical studies of particle acceleration. 5. Achievements - outstanding questions. Title: Energetic phenomena on the sun Authors: Kundu, Mukul Ranjan; Woodgate, Bruce; Schmahl, E. J. Bibcode: 1989epos.book.....K Altcode: 1989QB526.F6E52.... No abstract at ADS Title: Impulsive phase transport. Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.; Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose, D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.; Tanaka, K.; Zirin, H. Bibcode: 1989epos.conf..225C Altcode: The work of this group was concerned with how the energy released in a solar flare is transported through the solar atmosphere before escaping in the form of radiant and mechanical energy. Title: Three dimensional structures of coronal streamers, holes and CME plasmoids from multifrequency imaging observations Authors: Kundu, M. R.; Schmahl, E. J.; Gopalswamy, N.; White, S. M. Bibcode: 1989AdSpR...9d..41K Altcode: 1989AdSpR...9R..41K Throughout the quiet Sun years 1982-1987, the Clark Lake Radioheliograph routinely mapped the solar corona on a daily basis at frequencies from 30 to 100 MHz. The Clark Lake maps show a variety of features which we have analyzed quantitatively, providing information about the three dimensional nature of large scale structures of the solar corona. Title: First interferometric observations with arc-sec. resolution of solar radio bursts at millimeter wavelengths Authors: Kundu, Mukul R.; White, S. M.; Gopalswamy, N.; Bieging, J. H. Bibcode: 1989dots.work..119K Altcode: The Berkeley-Maryland-Illinois Array (BIMA) is briefly described in the context of solar observations. Specific areas of research that could be performed using BIMA during the Solar Maximum Mission (SMM) in 1991 are outlined. Some preliminary results of flare observations during March 1989 are presented. Title: Largescale Magnetic Field Phenomena Authors: Harrison, R. A.; Bentley, R. D.; Brosius, J.; Dwivedi, B. N.; Jardine, M.; Klimchuk, J. A.; Kundu, M. R.; Pearce, G.; Saba, J.; Sakurai, T.; Schmahl, E. J.; Schmelz, J.; Sime, D. G.; Steele, C. D. C.; Sun, M. T.; Tappin, S. J.; Waljeski, K.; Wang, A. H.; Wu, S. T. Bibcode: 1989tnti.conf....1H Altcode: No abstract at ADS Title: Microwave Evidence for Large-Scale Changes Associated with a Filament Eruption Authors: Kundu, M. R.; Schmahl, E. J.; Fu, Q. -J. Bibcode: 1989ApJ...336.1078K Altcode: VLA observations at 6 and 20 cm wavelengths taken on August 3, 1985 are presented, showing an eruptive filament event in which microwave emission originated in two widely separated regions during the disintegration of the filament. The amount of heat required for the enhancement is estimated. Near-simultaneous changes in intensity and polarization were observed in the western components of the northern and southern regions. It is suggested that large-scale magnetic interconnections permitted the two regions to respond similarly to an external energy or mass source involved in the disruption of the filament. Title: Millimeter wavelength observations of solar flares for Max 1991 Authors: Kundu, M. R.; Gopalswamy, N.; Nitta, N.; Schmahl, E. J.; White, S. M.; Welch, W. J. Bibcode: 1988fnsm.work..107K Altcode: The Hat Creek millimeter-wave interferometer (to be known as the Berkeley-Illinois-Maryland Array, BIMA) is being upgraded. The improved array will become available during the coming solar maximum, and will have guaranteed time for solar observing. The Hat Creek millimeter-wave interferometer is described along with the improvements. The scientific objectives are briefly discussed. Title: Detection of the dMe Flare Star YZ Canis Minoris Simultaneously at 20 and 90 Centimeter Wavelengths Authors: Kundu, M. R.; Shevgaonkar, R. K. Bibcode: 1988ApJ...334.1001K Altcode: The first aperture synthesis detection of the flare star YZ CMi at 90 cm wavelength is presented here. The simultaneous observations carried out at 20 and 90 cm wavelengths show that the emission at the two wavelengths is unipolar in the same sense and is uncorrelated. The high brightness temperature of ≡1013K at 90 cm wavelength strongly supports the coherent nature of the emission. The authors propose that the coherent emission is intrinsically unpolarized and the polarization is introduced by absorption in the higher coronal levels with large-scale magnetic fields, presumably the dipole magnetic field. Title: Modelling a C-type flare observed in microwaves and hard X-rays Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, Brian R. Bibcode: 1988fnsm.work..246S Altcode: Using the very large array (VLA) at 6 and 20 cm wavelength and the hard X-ray burst spectrometer on the Solar Maximum Mission, a two-ribbon flare was observed from the onset phase through the maximum and decline on November 14, 1981. Because of the extensive size of the microwave source and the gradual variations in hard X-rays whose spectrum becomes progressively flatter with time, the flare is classified as a C-type flare. Considering the hardening of the X-ray spectrum and its non-impulsive nature, a coronal trap model was invoked for the energetic electrons. The microwave emission is easily accounted for by gyrosynchronous radiation from mildly relativistic electrons. It was found that the source must be optically thick at 20 cm during the maximum phase, but as the source evolved toward an optically thin regime, the intensity decreased while the degree of circular polarization increased. In an initial homogeneous model, we found that the computed microwave spectrum was too narrow to match the patrol spectrum from 606 to 15400 MHz. In the model, the magnetic field consists of a dipolar arcade bridging the H alpha ribbons, and extending to heights of order 40,000 to 50,000 km. The variation of the magnetic field strength from footpoints to apex causes the gyrosynchrotron spectrum to be broader. Preliminary conclusions regarding the electron distributions producing the hard X-rays and the microwaves, and the suitability of this model for C-type flares is presented. Title: Current Loop Coalescence Model of Solar Flares: Erratum Authors: Tajima, T.; Sakai, J.; Nakajima, H.; Kosugi, T.; Brunel, F.; Kundu, M. R. Bibcode: 1988ApJ...329..517T Altcode: No abstract at ADS Title: Variability of Metric Emission from the Sun Authors: Shevgaonkar, R. K.; Kundu, M. R.; Jackson, P. D. Bibcode: 1988ApJ...329..982S Altcode: Full-disk observations of the sun obtained with the VLA at 317 MHz have been analyzed, with special attention being given to the short period variability of the meter-wavelength sources. A reduction in brightness is noted over coronal holes at 90 cm. Thermal emission models for the slowly varying component are investigated, along with a nonthermal emission mechanism for storm radiation at meter wavelengths. The results indicate that the thermal model encounters difficulties in accommodating short period changes over a few tens of minutes, and that the nonthermal mechanism encounters difficulty in accounting for the variability of low brightness temperatures of less than 10 to the 6th K. A gyrotron synchrotron emission mechanism has been ruled out. Title: High resolution microwave and X-ray observations of solar flares Authors: Alissandrakis, C. E.; Schadee, A.; Kundu, M. R. Bibcode: 1988A&A...195..290A Altcode: This paper presents an analysis of high spatial resolution observations of 18 weak flares, carried out during the Solar Maximum Year in the microwave range, H-alpha, and soft X-rays, together with observations of the associated hard X-ray emission and the photospheric magnetic field. This combination of observations made it possible to obtain a picture of the flare geometry and the relative position of the various emissions, to study the change of the geometry during the flare, to estimate the electron temperature and emission measure of the thermal plasma, and to compute the contribution of the free-free process in the microwave emission. Results are interpreted as evidence for the presence of energetic electrons even in the post-burst phase of some flares. There was also found a clear case of homologous radio and X-ray bursts, one case of foot-point expansion with a relative velocity of 20 km/s at 6.16 cm, as well as some evidence of triggering of flares by disturbances moving with a velocity of 5000-13,000 km/s. Title: Co-ordinated VLA and EXOSAT observations of the flrae stars UV Ceti, EQ Pegasi, YZ Canis Minoris and AD Leonis. Authors: Kundu, M. R.; Pallavicini, R.; White, S. M.; Jackson, P. D. Bibcode: 1988A&A...195..159K Altcode: The authors have observed four flare stars (UV Cet, EQ Peg, YZ CMi and AD Leo) simultaneously with the VLA and the EXOSAT satellite over continuous periods of 7 - 10 h. This is the first time that flare stars were observed simultaneously in X-rays and at microwave frequencies with high sensitivity instrumentation. All stars were detected both at the quiescent level and during flares. Although considerable activity in both X-rays and in the radio was found, there was little correlation between the two wavelength domains. The auhors discuss the significance of these observations for coronal activity in red dwarf flare stars. Title: An Eruptive Prominence and Associated Cm-Mm Emission Outside the Solar Limb Authors: Zodi, A. M.; Correia, E.; Costa, J. E. R.; Kaufmann, P.; Martin, S. F.; Kundu, M. R. Bibcode: 1988SoPh..116...83Z Altcode: We present radio maps at 22 and 44 GHz which show the emission before and after the eruption of a quiescent prominence located at the west limb. The observed radiation following the eruption is not consistent with thermal bremsstrahlung mechanism. It can be interpreted as due to gyrosynchrotron emission of nonthermal electrons. Our observations appear to be similar to the microwave radiation observed in post-flare loops; this radiation is due to nonthermal electrons trapped in the closed magnetic structures formed after the prominence eruption. Title: A Study of Coronal Bright Points at 20-CM Wavelength Authors: Nitta, N.; Kundu, M. R. Bibcode: 1988SoPh..117...37N Altcode: We present the results of a study of coronal bright points observed at 20 cm with the VLA on a day when the Sun was exceptionally quiet. Microwave maps of bright points were obtained using data for the entire observing period of 5 hours, as well as for shorter periods of a few minutes. Most bright points, especially those appearing in the full-period maps appear to be associated with small bipolar structures on the photospheric magnetogram. Overlays of bright point (B.P.) maps on the Ca+K picture, show that the brightest part of a B.P. tends to lie on the boundary of a supergranulation network. In general, the bright points exhibit rapid variations in intensity. There is no systematic correlation between the size of a B.P. and its intensity; the apparently slow variation of B.P. emission may have rapid fluctuations superimposed on it. Title: Modelling a C-Type Flare Observed in Microwaves and Hard X-rays Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R. Bibcode: 1988BAAS...20R.748S Altcode: No abstract at ADS Title: Millimeter Wavelength Observations of Solar Flares for Max'91 Authors: Kundu, M. R.; Gopalswamy, N.; Nitta, N.; Schmahl, E. J.; White, S. M. Bibcode: 1988BAAS...20..746K Altcode: No abstract at ADS Title: Moving Radio Loop Structure During a Fast CME Authors: Gopalswamy, N.; Kundu, M. R.; Hundhausen, A. Bibcode: 1988BAAS...20Q.682G Altcode: No abstract at ADS Title: Slowly-Varying Observed with the Clark Lake Radioheliograph Authors: Schmahl, E. J.; Kundu, M. R.; Gopalswamy, N.; Jackson, P. D. Bibcode: 1988BAAS...20..712S Altcode: No abstract at ADS Title: A VLA Survey of dM Stars Covering a Broad Range in X-ray Fluxes Authors: Kundu, M. R.; White, S. M.; Agrawal, P. C. Bibcode: 1988BAAS...20..696K Altcode: No abstract at ADS Title: Coronal Bright Points at 6 and 20 Centimeter Wavelengths Authors: Kundu, M. R.; Schmahl, E. J.; Fu, Q. -J. Bibcode: 1988ApJ...325..905K Altcode: The paper presents the results of near-simultaneous observations of bright points at 6 and 20 cm for a time interval of 10 hr using the VLA. It is shown that, at both 6 and 20 cm, the radio sources in the quiet sun have a very close association with bipolar features seen in magnetograms and with dark features in He I 10830 A spectroheliograms. The paper discusses the associations and the distributions of size, brightness, and temporal variation of the microwave bright points. It is found that the brightness temperatures of the 6 and 20 cm bright points are in the approximate ratio 0.09:1 expected from the emission mechanism being thermal bremsstrahlung. Title: Large scale structure of the Sun's corona. Authors: Kundu, Mukul R. Bibcode: 1988sscd.conf..192K Altcode: The author reviews some results concerning the large scale structure of the Sun's corona, obtained with the imaging observations of the Sun at meter-decameter wavelengths, using the Clark Lake multifrequency radioheliograph. Title: Quasi-dedicated millimeter wave imaging observations of solar flares during next solar maximum Authors: Kundu, M. R. Bibcode: 1988AdSpR...8k..33K Altcode: 1988AdSpR...8...33K A brief description of the Berkeley-Illinois-Maryland Millimeter Array (BIMA) for synthesis mapping of the Sun and other sources is given here. The array will be used in a quasi-dedicated mode to observe solar flares. The main scientific objectives will be to obtain positional and structural information of millimeter solar bursts and to study high energy flare physics and the role of electron beams in producing Hα, EUV and white light emission. Other studies will be concerned with active regions, filaments and coronal holes at millimeter wavelengths. Title: Coronal bright points at 6cm wavelength Authors: Fu, Qijun; Kundu, M. R.; Schmahl, E. J. Bibcode: 1988VA.....31..103F Altcode: Results are presented from observations of bright points at a wavelength of 6-cm using the VLA with a spatial resolution of 1.2 arcsec. During two hours of observations, 44 sources were detected with brightness temperatures between 2000 and 30,000 K. Of these sources, 27 are associated with weak dark He 10830 A features at distances less than 40 arcsecs. Consideration is given to variations in the source parameters and the relationship between ephemeral regions and bright points. Title: Coronal bright points in mircrowaves. Authors: Kundu, M. R.; Nitta, N. Bibcode: 1988sscd.conf...89K Altcode: An excellent map of the quiet Sun showing coronal bright points at 20 cm wavelength was produced using the VLA on February 13, 1987. The authors studied the locations of bright points relative to features on the photospheric magnetogram and Ca+K spectroheliogram. They find that most bright points appearing in the full 5-hour synthesized map are associated with small bipolar structures on the photospheric magnetogram; and the brightest part of a B.P. tends to lie on the boundary of a supergranulation network. The bright points exhibit rapid variations in intensity superposed on an apparently slow variation. Title: Variability of meter wavelength solar radio emission. Authors: Shevgaonkar, R. K.; Kundu, M. R. Bibcode: 1988sscd.conf..248S Altcode: A study of the variability of solar radio emission at 90 cm wavelength using the VLA is presented. The VLA observations have been supplemented by meter and decameter wavelength observations obtained simultaneously with the Clark Lake radioheliograph. 90 cm sources are well correlated with Hα filaments; decameter sources are also correlated with coronal holes. Various emission mechanisms have been examined to explain the short period variability of the meter wavelength sources. The plasma radiation at the fundamental plasma frequency, as has been proposed for storm radiation appear to be the most acceptable emission mechanism, provided the source filling factor is less than a few percent. Title: A two-zone model of coronal hole structure in the high corona. Authors: Wang, Zhengzhi; Yoshimura, H.; Kundu, M. R. Bibcode: 1988sscd.conf..458W Altcode: The authors propose a two-zone model of coronal hole structure in the high corona at height around 1.5 to 1.7 solar radii, in which a central zone and a boundary zone can be clearly distinguished. The model is suggested by comparing the results of computation of potential magnetic fields of the corona and meter-decameter radio observations. The coronal magnetic fields were computed from the surface field observed at the John M. Wilcox Solar Observatory at Stanford University. The radio data were obtained at the Clark Lake Radio Observatory of the University of Maryland. The location of a coronal hole at the base of the corona is determined with the help of He I 10830 Å maps observed at the National Solar Observatory at Kitt Peak. Title: Current Loop Coalescence Model of Solar Flares Authors: Tajima, T.; Sakai, J.; Nakajima, H.; Kosugi, T.; Brunel, F.; Kundu, M. R. Bibcode: 1987ApJ...321.1031T Altcode: A computer simulation and theoretical study of the physical characteristics of the explosive coalescence of current-carrying loops is presented. Characteristics of the explosive coalescence include a large impulsive increase of the kinetic energies of electrons and ions, the simultaneous heating and acceleration of electrons and ions in high and low energy ranges, and a break in the energy spectra of electrons and ions. A characteristic double subpeak structure is found in the quasi-periodic oscillations found in the time profiles of the solar flares of June 7, 1980 and November 26, 1982 which can be explained in terms of the coalescence instability of two current loops. Title: Simultaneous 2 and 6 Centimeter Wavelength Observations of a Solar Flare Using the VLA Authors: Kundu, M. R.; Velusamy, T.; White, S. M. Bibcode: 1987ApJ...321..593K Altcode: VLA observations of a solar active region and a flare are discussed. The event was observed at wavelengths of 2 and 6 cm simultaneously. Radio maps prior to the flare delineate the most important magnetic structures in the region. Interaction between these structures apparently led to preheating of plasma above the active region some 30 minutes prior to the flare. The 2 and 6 cm flare positions were coincident, and the time profiles of the burst at the two wavelengths were almost identical, implying that the same population of electrons was responsible for emission at the two wavelengths. Emission was probably nonthermal gyrosynchrotron radiation, and the physical conditions in the burst source are derived using this assumption. Title: The Effect of a Large Flare on the Solar Corona Authors: Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.; Schmahl, E. J.; Kundu, M. R. Bibcode: 1987BAAS...19S1122S Altcode: No abstract at ADS Title: Imaging observations of the evolution of meter-decameter burst emission during a major flare. Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1987SoPh..111..347G Altcode: We present the results of a study of the evolution of 3 February, 1986 flare at meter-decameter wavelengths using the two dimensional imaging observations made with the Clark Lake multifrequency radioheliograph. The flare was complex and produced various types of meter-decameter bursts. The preflare activity was observed in the form of type III bursts some tens of minutes prior to the impulsive onset. From the positional analysis of the preflare and impulsive phase type III bursts and other measured characteristics we discuss the characteristics of energy release and possible magnetic field configurations in the vicinity of energy release region. From positional and temporal studies of the flare continuum and type II burst in relation to the microwave and hard X-ray emissions, we discuss the possible magnetic field structures in which the accelerated particles are confined or along which they propagate. We develop a schematic model of the flaring region based upon our study. Title: Meterwave observations of a coronal hole. Authors: Wang, Z.; Schmahl, E. J.; Kundu, M. R. Bibcode: 1987SoPh..111..419W Altcode: We present meterwave maps showing a coronal hole at 30.9, 50.0, and 73.8 MHz using the Clark Lake Radioheliograph in October 1984. The coronal hole seen against the disk at all three frequencies shows interesting similarities to, and significant differences from its optical signatures in He Iλl10830 spectroheliograms. Title: Coronal Bright Points in Microwaves: Their Optical Associations and Emission Measures Authors: Nitta, N.; Kundu, M. R. Bibcode: 1987BAAS...19.1122N Altcode: No abstract at ADS Title: Characteristics of shock-associated fast-drift kilometric radio bursts. Authors: MacDowall, R. J.; Stone, R. G.; Kundu, M. R. Bibcode: 1987SoPh..111..397M Altcode: The existence of a class of fast-drift, shock-associated (SA), kilometric radio bursts which occur at the time of metric type II emission and which are not entirely the kilometric continuation of metric type III bursts has been reported previously (Cane et al., 1981). In this paper, we establish unambiguous SA event criteria for the purpose of statistically comparing SA events with conventional kilometric type III bursts. We apply these criteria to all long-duration, fast-drift bursts observed by the ISEE-3 spacecraft during a 28-month interval and find that more than 70% of the events satisfying the criteria are associated with the radio signatures of coronal shocks. If a given event in our sample is associated with a metric type II or type IV burst, it is 13 times more likely to satisfy the SA criteria than an event associated only with metric type III activity. Compared with conventional kilometric type III bursts, the characteristics of these SA events are longer duration, higher maximum intensity, and a larger number of components. Differences in these characteristics for the two classes of events are not sufficient to distinguish all SA events from conventional type III bursts. The consistent lack of reported metric type III activity during the latter part of the candidate events suggests that some of the electrons are accelerated high in the corona, at or near the altitude of the shock. Title: A Study of Solar Preflare Activity Using Two-Dimensional Radio and Smm/xrp Observations Authors: Kundu, M. R.; Gopalswamy, N.; Saba, J. L. R.; Schmelz, J. T. S.; Strong, K. T. Bibcode: 1987SoPh..114..273K Altcode: We present a study of type III activity at meter- decameter wavelengths in the preflare phase of the 1986 February 3 flare using data obtained with the Clark Lake Multifrequency Radioheliograph. We compare this activity with similar type III burst activity during the impulsive phase and find that there is a displacement of burst sources between the onset and end times of the activity. A comparison of this displacement at three frequencies suggests that the type III emitting electrons gain access progressively to diverging and different field lines relative to the initial field lines. The energetics of the type III emitting electrons are inferred from observations and compared with those of the associated hard X-ray emitting electrons. The soft X-ray data from SMM-XRP shows enhanced emission measure, density and temperature in the region associated with the preflare type III activity. Title: Simultaneous radio and white light observations of the 1984 June 27 coronal mass ejection event Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1987SoPh..114..347G Altcode: We present the two-dimensional imaging observations of radio bursts in the frequency range 25-50 MHz made with the Clark Lake multifrequency radioheliograph during a coronal mass ejection event (CME) observed on 1984, June 27 by the SMM Coronagraph/Polarimeter and Mauna Loa K-coronameter. The event was spatially and temporally associated with precursors in the form of meter-decameter type III bursts, soft X-ray emission and a Hα flare spray. The observed type IV emission in association with the CME (and the Hα spray) could be interpreted as gyrosynchrotron emission from a plasmoid containing a magnetic field of ∼2.5 G and nonthermal electrons with a number density of ∼ 105 cm−3 and energy ≳350 keV. Title: Quiet Sun and Slowly Varying Component at Meter and Decameter Wavelengths Authors: Lantos, P.; Alissandrakis, C. E.; Gergely, T.; Kundu, M. R. Bibcode: 1987SoPh..112..325L Altcode: Comparison of maps of the Sun obtained over the period June 29 to July 8, 1982 at 169 MHz with the Nançay Radioheliograph and at 73.8, 50, and 30.9 MHz with the Clark Lake Radioheliograph shows that the slowly varying component at meter and decameter wavelengths is not always thermal emission. During the period under study weak noise storm continua were the most frequent sources of slowly varying component at 169 and 73.8 MHz. Most filaments show no radio counterpart on the disk. A streamer has been detected on the disk from 169 to 30.9 MHz with an optimum observability at 50 MHz. The brightest source of the slowly varying component from 73.8 to 30.9 MHz for most of the period was located above an extended coronal hole in a region where a depression was observed at 169 MHz. In favorable cases, electron densities can be derived from the positions of noise storms and radio streamers; these are in agreement with previous K-corona eclipse observations. Title: Two dimensional imaging observations of meter-decameter bursts associated with the February 1986 flare activity Authors: Gopalswamy, N.; Kundu, M. R. Bibcode: 1987sici.symp...16G Altcode: An analysis is presented of the two dimensional imaging observations of a flare observed on 3 Feb. l986 using the Clark Lake Multifrequency Radioheliograph. The flare produced almost all types of Meter-decimeter radio emission: enhanced storm radiation, type III/V bursts, II and IV and flare continuum. The flare continuum had early (FCE) and late (FC II) components and the type II occurred during the period between these two components. Comparing the source positions of type III/V and FCE it was found that these bursts must have occurred along adjacent open and closed field lines, respectively. The positional analysis of type II and FC II implies that the nonthermal electrons responsible for FC II need not be accelerated by type II shock and this conclusion is further supported by the close association of FC II with a microwave peak. Using the positional and temporal analysis of all these bursts and the associated hard X-ray and microwave emissions, a schematic model is developed for the magnetic field configuration in the flaring region in which the nonthermal particles responsible for these bursts are confined or along which they propagate. Title: Microwave Observations of the X-Flare of May 19, 1984 Authors: Schmahl, E. J.; Kundu, M. R.; Schmelz, J. T.; Saba, J.; Strong, K. T. Bibcode: 1987BAAS...19R1122S Altcode: No abstract at ADS Title: Propagation of Electrons Emitting Weak Type-Iii Bursts in Coronal Streamers Authors: Gopalswamy, N.; Kundu, M. R.; Szabo, A. Bibcode: 1987SoPh..108..333G Altcode: We report the observations of weak type III bursts at 73.8, 57.5, 50.0, and 38.5 MHz from Clark Lake Radio Observatory on four days and discuss their characteristics. In addition to Clark Lake data, the magnetogram and sunspot/active region data and the coronal streamer data obtained by HAO's Coronagraph/Polarimeter aboard SMM satellite are used to study the location of the burst sources with respect to the coronal streamers emanating from active regions. It is shown that the bursts occur within or close to the edge of dense coronal streamers implying that the coronal streamers contain open magnetic field lines along which the electrons generating the bursts propagate. The positional analysis of the bursts is used to estimate the variation of coronal electron density with radial distance. Title: Meterwave observations of a coronal hole Authors: Wang, Z.; Schmahl, E. J.; Kundu, M. R. Bibcode: 1987sici.symp...24W Altcode: Meter-wave maps are presented showing a coronal hole at 30.9, 50.0, and 73.8 MHz using the Clark Lake Radioheliograph in October 1984. The coronal hole seen against the disk at all three frequencies shows interesting similarities to, and significant differences from its optical signatures in HeI lambda10830 spectroheliograms. The 73.8 MHz coronal hole, when seen near disk center, appears to coincide with the HeI footprint of the hole. At the lower frequencies, the emission comes from higher levels of the corona, and the hole appears to be displaced, probably due to the non-radial structure of the coronal hole. The contrast of the hole relative to the quiet Sun is much greater than reported previously for a coronal hole observed at 80 MHz. The higher contrast is certainly real, due to the superior dynamic range, sensitivity, and calibration of the Clark Lake instrument. Using a coronal hole model, the electron density is derived from radio observations of the brightness temperature. A very large discrepancy is found between the derived density and that determined from Skylab EUV observations of coronal holes. This discrepancy suggests that much of the physics of coronal holes has yet to be elucidated. Title: Radio studies of large scale structures of the Sun's corona and transient activity Authors: Kundu, Mukul R. Bibcode: 1987sici.symp...22K Altcode: The use of meter-decimeter wavelength imaging observations for four different kinds of studies of solar coronal activity is discussed. (1) Large scale structure of the upper corona; daily imaging observations permit comparison of radio images with white light images from space and ground observation, generation of synoptic charts similar to white light coronagraph synoptic charts, and comparison of radio brightness enhancements and deficiencies with bright coronal streamers and coronal holes. (2) Relative positions of type III burst sources and coronal streamers as observed by Solwind experiment on the P-78-1 satellite and by the HAO C/P experiment aboard the SMM; infer the paths of type III emitting electrons in dense coronal streamers, and from multifrequency observations derive electron density distributions above active regions near the limb. (3) Non-flare associated type II/type IV bursts associated with coronal streamer disruption events; such type IV sources have a rather slow velocity (approx = to or less than 100 km/s) CMEs. (4) Meter-decimeter microbursts; these are short duration (2-10 sec) weak-type III-like bursts, produced at the fundamental plasma frequency by plasma radiation processes which have important differences from the standard mechanisms used to explain the strong type III bursts. Title: Simultaneous VLA Observations of a Flare at 6 and 20 Centimeter Wavelengths Authors: Velusamy, T.; Kundu, M. R.; Schmahl, E. J.; McCabe, M. Bibcode: 1987ApJ...319..984V Altcode: Using the Very Large Array at 6 and 20 cm wavelengths, a May 15, 1980 solar flare was mapped. The 1B flare, as observed in H alpha at Mees Solar Observatory, Maui, Hawaii, appeared as two sequential flares occurring at different neutral lines. The peaks of the time profile at 20 cm were delayed with respect to the 6 cm counterparts, but they were related to each other and to the H alpha activity. At 20 cm, precursor activity occurred, and an oppositely polarized source an arcminute away from the main burst may have triggered the flare. The main 20 cm emission appeared to be displaced limbward from the 6 cm burst. If both the 6 and 20 cm emission originated in the same system of loops, it is inferred that the apparent lateral displacement was caused by a height difference of 33,000 km in the sources of emission. Title: A study of hard X-ray associated meter-decameter bursts observed on December 19, 1979 Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R.; Sawant, H. S. Bibcode: 1987STIN...8728486K Altcode: The results of a study of the relationship of a complex meter-decameter wavelength radio burst observed with the Clark Lake E-W and N-S interferometers, with a hard X-ray burst observed with the X-ray spectrometer aboard ISEE-3 are presented. The radio burst consisted of several type III's, reverse drift type III's, a U burst, and type II and type IV bursts. The X-ray emission was also complex. The radio as well as hard X-ray emissions were observed before the flash phase of the flare; they were not always associated and it is conjectured that this may constitute evidence for acceleration of electrons high in the corona. On the other hand, all components of the reverse drift burst were associated with hard X-ray subpeaks, indicating multiple injection of electron beams along field lines with different density gradients. While the type II burst appeared to be related to the hard X-ray burst, a detailed correspondence between individual features of the radio and hard X-ray burst emissions could not be found. The type IV burst started after all hard X-ray emissions ceased. Its source appeared to be a magnetic arch, presumably containing energetic electrons responsible for the gyrosynchrotron radiation of type IV. Title: Coronal Bright Points at 6 and 20 cm Wavelengths Authors: Kundu, M. R.; Schmahl, E. J.; Jackson, P. D.; Fu, Q. -J. Bibcode: 1987BAAS...19..937K Altcode: No abstract at ADS Title: Comparison of Large Scale Structures of the Corona in White Light and Radio Wavelengths Authors: Jackson, P. D.; Kundu, M. R. Bibcode: 1987BAAS...19..931J Altcode: No abstract at ADS Title: Soft X-Ray, Microwave and Delayed Hard X-Ray Emission From Interacting Solar Flare Loops Authors: Holman, Gordon D.; Kundu, Mukul R. Bibcode: 1987BAAS...19..925H Altcode: No abstract at ADS Title: Microwave Evidence for Large Scale Magnetic Rearrangements Associated with a Filament Eruption Authors: Schmahl, E. J.; Kundu, M. R.; Fu, Q. -J. Bibcode: 1987BAAS...19..925S Altcode: No abstract at ADS Title: Dynamic Spectrum of a Radio Flare on UV Ceti Authors: Jackson, Peter D.; Kundu, Mukul R.; White, Stephen M. Bibcode: 1987ApJ...316L..85J Altcode: The dMe flare star UV Ceti (L726-8B) was observed at four frequencies simultaneously in the 1385-1652 MHz band using the Very Large Array. A flare lasting 10 minutes was observed with 6.67 s time resolution 'Dynamic spectrum'-type images in the Stokes parameters I and V show considerable complexity in the frequency-time domain; some features show a positive frequency drift with time, while others are more complex, involving both positive and negative frequency drifts. The positive drift features would be consistent with disturbances traveling downward in the star's corona. Title: The Plasma and Magnetic Field Properties of Coronal Loops Observed at High Spatial Resolution Authors: Webb, D. F.; Holman, G. D.; Davis, J. M.; Kundu, M. R.; Shevgaonkar, R. K. Bibcode: 1987ApJ...315..716W Altcode: Two data sets are analyzed in order to improve understanding of the plasma and magnetic field properties of active region coronal loops. Each set consists of coaligned, high spatial resolution soft X-ray, microwave, and magnetogram images that are used to compare observations of coronal loops and their feet in the photosphere and to constrain possible microwave emission mechanisms. The loops are found to have plasma parameters typical of quiescent active region loops. Each loop has a compact microwave source with peak brightness temperature T(b) = 1-2.5 x 10 to the 6th K cospatial with or near the loop apex. No complete loops are imaged in microwaves. The loop emission observed at 4.9 GHz is best described by fourth harmonic gyroresonance emission from a dipole loop model, but with less field variation along the loop than in the models of Holman and Kundu (1985). Title: Very-large-array observations of a complex gradual solar burst at 6 CM wavelength Authors: Kundu, M. R.; McConnell, D.; White, S. M.; Shevgaonkar, R. K. Bibcode: 1987A&A...176..131K Altcode: The authors present a 6 cm VLA observation of a burst from a solar active region. The burst shows a normal impulsive rise-and-fall superimposed on a gradual component. The peak brightness temperature of the burst remains relatively constant, and the flux variations are due to changes in the source structure. It appears as though an arcade of loops is gradually heated or filled with hot plasma. The burst is weakly polarized but unipolar; the authors investigate the possible reasons for this structure. Depolarization of optically thin emission due to twisted magnetic fields within the source can produce significant depolarization, but is probably not active in this event. Instead, it is suggested that the flare emission is optically thick and that hot overlying material preferentially absorbs one polarization. Title: Large-scale structure of the sun's corona from radio observations using the Clark Lake Radioheliograph Authors: Kundu, M. R.; Gergely, T. E.; Schmahl, E. J.; Szabo, A.; Loiacono, R.; Wang, Z.; Howard, R. A. Bibcode: 1987SoPh..108..113K Altcode: We present meterwave maps of the solar corona made with the Clark Lake Radioheliograph at 30.9, 50, and 73.8 MHz for one solar rotation. We compare and contrast them with optical data: 10830 Å maps, white-light coronagraph images (SOLWIND and Mauna Loa K coronameter) and forbidden line scans. Most of the sources in the radio maps persist for two days or more, and appear to rotate approximately with the solar rate. A coronal hole seen against the disk at all three frequencies shows interesting similarities and significant differences with the optical signatures of the hole. Elongated features of the 50 MHz corona correspond rather well to the azimuthal position of white light streamers seen in SOLWIND images. Synoptic charts made from the radio maps show overall similarities to synoptic charts constructed from (limb) coronagraph data. Some of the differences may result from the different weightings given by the radio and optical data to density and temperature, or by the different sensitivities to non-radial geometries. We show that the combined use of meter wave and optical images provide considerable new insights into the three-dimensional structure of the low to middle corona. Title: Correlated Type-Iii Burst Emission from Distant Sources on the Sun Authors: Kundu, M. R.; Gopalswamy, N. Bibcode: 1987SoPh..112..133K Altcode: We report the observation and interpretation of a correlated type III burst emitted from distant sources on the Sun. The angular separation between the distant sources is as large as 26' or ∼ 106 km. There was an active region ∼ 30° behind the limb, and it is believed that the type III burst emission originated from activity in this region. The implications of the locations of the correlated sources with regard to the geometry of the magnetic structures involved in the flare process are discussed. Title: Coronal Bright Points at 6-CM Wavelengths Authors: Fu, Q.; Kundu, M. R.; Schmahl, E. J. Bibcode: 1987SoPh..108...99F Altcode: We report the results of the first observations of solar coronal bright points at 6 cm wavelength using the Very Large Array (VLA), with a spatial resolution of ∼ 1″.2. The maximum brightness temperature of the sources observed is ≈ 3 × 104 K with a mean value of ≈ 1 × 104 K (above the quiet Sun value). The lifetime of most sources is between 5 and 20 min. The average diameter of the sources is about 5-15″ arc. The sources are gaussian-like near the footpoint of miniature loops and they appear in groups. The observations indicate that significant fluctuations in the brightness temperature (sometimes quasi-periodic) and in the spatial extents of these sources can occur over periods of a few minutes. Title: A Type-Iv Burst Associated with a Coronal Streamer Disruption Event Authors: Kundu, M. R. Bibcode: 1987SoPh..111...53K Altcode: A type IV burst was observed on February 17, 1985 with the Clark Lake Radio Observatory multifrequency radioheliograph operating in the frequency range 20-125 MHz. This burst was associated with a coronal streamer disruption event. From two-dimensional images produced at 50 MHz, we show evidence of a type II burst and a slow moving type IV burst. The observations of the moving type IV burst suggests that a plasmoid containing energetic electrons can result from the disruption of a coronal streamer. Title: The Sun's outer corona at radio wavelengths. Authors: Kundu, Mukul R. Bibcode: 1987IJRSP..16..172K Altcode: The use of meter-decameter wavelength imaging observations to follow four different kinds of studies of solar coronal activity is discussed. The Clark Lake Radio Observatory's multifrequency radioheliograph which operates in the 20-125 MHz frequency range is described. This paper emphasizes the differences observed in coronal phenomena with instruments having a higher sensitivity than the Culgoora instrument. New observations from the Clark Lake radioheliograph which show details of the long-lived structure of the corona are presented. These are then compared with features of the optical corona as shown in the data obtained by satellite-borne and ground-based coronagraphs. Title: 6 and 20 cm wavelength observations of coronal bright points Authors: Kundu, M. R.; Schmahl, E. J.; Fu, Q. J. Bibcode: 1987SoPh..113..305K Altcode: 1982SoPh..113..305K No abstract at ADS Title: Imaging observations of radio bursts at meter-decameter wavelengths Authors: Kundu, Mukul R. Bibcode: 1987SoPh..113...87K Altcode: 1982SoPh..113...87K In this article, we review some of the recent results obtained with imaging observations of the Sun at meter-decameter wavelengths, using the Clark Lake multifrequency radioheliograph. We briefly discuss the use of imaging observations to study the large scale structure of the upper corona. We discuss non-flare associated type II/type IV bursts associated with a coronal streamer disruption event associated with a slow (≤100 Km/s) CME. We discuss meter-decameter microbursts, which occur at coronal heights, often without any surface activity. Finally, we discuss a correlated type III burst whose emission originates almost simultaneously from two widely separated (≳ 105 Km) locations. Title: Microwave Observations of Red Dwarf Flare Stars Authors: Kundu, M. R.; Jackson, P. D.; White, S. M. Bibcode: 1987LNP...291..100K Altcode: 1987LNP87.291..100K; 1987csss....5..100K No abstract at ADS Title: A VLA Survey of dMe Flare Stars Authors: Jackson, P. D.; Kundu, M. R.; White, S. M. Bibcode: 1987LNP...291..103J Altcode: 1987csss....5..103J; 1987LNP87.291..103J A survey is underway, which uses the VLA at wavelengths of 6 and 20 cm, to search for radio emission from all dMe flare star. within about 10 parsecs of the Sun, and which have not yet been widely observed at radio wavelengths. At 20 cm, two bands centered at 1415 and 1515 MHz are observed and at 6 cm, two bands centered at 4535 and 4985 MHz are observed. Results so far, based on a total observing time of about one hour each during July 1986 have yielded detections from 9 of the 27 stellar systems in the program. Title: Multiwavelength Microwave Observations of Solar Active Regions and Flares Authors: Kundu, M. R. Bibcode: 1987sman.work...25K Altcode: A preflare active region was studied using the Very Large Array (VLA) at 2, 6 and 20 cm. The author also carried out simultaneous observations of a microwave burst at 2 and 6 cm wavelengths with the VLA. Title: Microwave Observations of Flare Stars UV Ceti, AT Microscopii, and AU Microscopii Authors: Kundu, M. R.; Jackson, P. D.; White, S. M.; Melozzi, M. Bibcode: 1987ApJ...312..822K Altcode: The results of observations of three red dwarf flare star systems, UV Ceti, AT Mic, and AU Mic, made in February and March of 1985, are reported. Flaring was detected from all three systems, and quiescent emission from UV Cet and AU Mic. Models for the quiescent microwave-emitting corona of UV Cet are discussed. The gravitational scale height in current models is similar to or larger than the height of the corona, which is a striking difference from the case of the solar corona and confirms that magnetic structures are required to confine the radio-emitting corona. The role of precipitation into the chromosphere of the energetic particles in such a corona is explored, and it is shown that for plausible parameters it may be the dominant energy loss mechanism. Title: Impulsive Phase Observations and Their Interpretation Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.; Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose, D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.; Tanaka, K.; Zirin, H. Bibcode: 1986epos.conf..3.4C Altcode: 1986epos.confC...4C No abstract at ADS Title: Phenomena Associated with Ions and Relativistic Electrons Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.; Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.; Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.; Tsuneta, S.; van Hoven, G. Bibcode: 1986epos.conf.2.30V Altcode: 1986epos.confB..30V No abstract at ADS Title: Theoretical Studies of Transport Processes Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.; Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose, D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.; Tanaka, K.; Zirin, H. Bibcode: 1986epos.conf.3.34C Altcode: 1986epos.confBC.34C No abstract at ADS Title: Impulsive phase transport Authors: Canfield, Richard C.; Bely-Dubau, Francoise; Brown, John C.; Dulk, George A.; Emslie, A. Gordon; Enome, Shinzo; Gabriel, Alan H.; Kundu, Mukul R.; Melrose, Donald; Neidig, Donald F. Bibcode: 1986epos.conf..3.1C Altcode: 1986epos.confC...1C The transport of nonthermal electrons is explored. The thick-target electron beam model, in which electrons are presumed to be accelerated in the corona and typically thermalized primarily in the chromosphere and photosphere, is supported by observations throughout the electromagnetic spectrum. At the highest energies, the anisotropy of gamma-ray emission above 10 MeV clearly indicates that these photons are emitted by anisotropically-directed particles. The timing of this high-energy gamma-radiation with respect to lower-energy hard X-radiation implies that the energetic particles have short life-times. For collisional energy loss, this means that they are stopped in the chromosphere or below. Stereoscopic (two-spacecraft) observations at hard X-ray energies (up to 350 keV) imply that these lower-energy (but certainly nonthermal) electrons are also stopped deep in the chromosphere. Hard X-ray images show that, in spatially resolved flares whose radiation consists of impulsive bursts, the impulsive phase starts with X-radiation that comes mostly from the foot-points of coronal loops whose coronal component is outlined by microwaves. Title: Mechanisms for Particle Accleration in Flares Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.; Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.; Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.; Tsuneta, S.; van Hoven, G. Bibcode: 1986epos.conf.2.42V Altcode: 1986epos.confB..42V No abstract at ADS Title: Three-dimensional structures of solar active regions. Authors: Kundu, M. R. Bibcode: 1986NASCP2442..291K Altcode: 1986copp.nasa..291K Three dimensional structure of an active region is determined from observations with the Very Large Array (VLA) at 2, 6, and 20 cm. This region exhibits a single magnetic loop of length approx. 10 to the 10th power cm. The 2 cm radiation is mostly thermal bremsstrahlung and originates from the footpoints of the loop. The 6 and 20 cm radiation is dominated by the low harmonic gyroresonance radiation and originates from the upper portion of the legs or the top of the loop. The loop broadens toward the apex. The top of the loop is not found to be the hottest point, but two temperature maxima on either side of the loop apex are observed, which is consistent with the model proposed for long loops. From 2 and 6 cm observations it can be concluded that the electron density and temperature cannot be uniform in a plane perpendicular to the axis of the loop; the density should decrease away from the axis of the loop. Title: VLA observations of solar filaments at 6 and 20 cm wavelengths. Authors: Kundu, M. R. Bibcode: 1986NASCP2442..117K Altcode: 1986copp.nasa..117K Using the Very Large Array the author observed several solar filaments at 1.5 and 5 GHz. The brightness temperatures of the filaments are 4 - 5×104K at 20 cm and 1.5 - 1.6×104K at 6 cm. The maximum temperature depressions appear to be associated with Hα filaments. Comparison with He 10830 Å spectroheliogram shows that 20 cm temperature depressions correspond to the regions of reduced intensity in the He 10830 Å around filaments, which correspond to coronal cavities. The author studied the temperature and density structure of the transition sheath between the filament and the surrounding corona assuming that the energy radiated away is balanced by the energy conducted from the corona. He found that the observations can be better explained by a model having a pressure gradient in the transition sheath around the filament. Title: VLA observations of coronal bright points at 6 and 20 cm wavelengths. Authors: Kundu, M. R. Bibcode: 1986NASCP2442..349K Altcode: 1986copp.nasa..349K Prior to and during the Spacelab-2 operation, observations were made at 6 and 20 cm of solar coronal bright points, using the Very Large Array (VLA) in the C-configuration. The ultraviolet coverage ranged from 200 to 18,000 wavelengths. The maps were convolved with beams of 18 x 18 inches at 20 km and 4 x 4 inches at 6 cm. Only the preliminary results from July 15 and July 31, 1985 observations. Title: Energetic Phenomena on the Sun: The Solar Maximum Mission Flare Workshop. Proceedings Authors: Kundu, Mukul; Woodgate, Bruce Bibcode: 1986epos.conf.....K Altcode: No abstract at ADS Title: Large scale structure of the sun's radio corona. Authors: Kundu, M. R. Bibcode: 1986NASCP2442..253K Altcode: 1986copp.nasa..253K The author presents results of studies of large scale structures of the corona at long radio wavelengths, using data obtained with the multifrequency radioheliograph of the Clark Lake Radio Observatory. He shows that features corresponding to coronal streamers and coronal holes are readily apparent in the Clark Lake maps. Title: Narrow-Band Radio Flares from Red Dwarf Stars Authors: White, Stephen M.; Kundu, Mukul R.; Jackson, Peter D. Bibcode: 1986ApJ...311..814W Altcode: VLA observations of narrow-band behavior in 20 cm flares from two red dwarf stars, L726 - 8A and AD Leo, are reported. The flare on L726 - 8A was observed at 1415 and 1515 MHz; the flux and the evolution differed significantly at the two frequencies. The flare on AD Leo lasted for 2 hr at 1415 MHz but did not appear at 1515 MHz. The AD Leo flare appears to rule out a source drifting through the stellar corona and is unlikely to be due to plasma emission. In the cyclotron maser model the narrow-band behavior reflects the range of magnetic fields present within the source. The apparent constancy of this field for 2 hr is difficult to understand if magnetic reconnection is the source of energy for the flare. The consistent polarization exhibited by red dwarf flares at 20 cm may be related to stellar activity cycles, and changes in this polarization will permit measuring the length of these cycles. Title: Large scale structure of the corona. Authors: Kundu, M. R. Bibcode: 1986NASCP2442..249K Altcode: 1986copp.nasa..249K This is an introduction to this section of the proceedings. In this section is a brief description of some radio results obtained with meter-decameter radioheliograph. An optical study based upon synoptic data of polarized brightness (pB), H alpha line filtergrams and large scale B-fields is presented. This is followed by two papers on the interpretation of coronal mass ejection (CME) and modeling of three dimensional coronas. Title: Phenomena Associated with Mildly Relativistic Electrons Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.; Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.; Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.; Tsuneta, S.; van Hoven, G. Bibcode: 1986epos.conf..2.2V Altcode: 1986epos.confB...2V No abstract at ADS Title: A study of solar filaments from high resolution microwave observations Authors: Kundu, M. R.; Melozzi, M.; Shevgaonkar, R. K. Bibcode: 1986A&A...167..166K Altcode: Using the Very Large Array the authors have observed several solar filaments at 1.5 and 5 GHz. The brightness temperatures of the filaments are 4 - 5×104K at 20 cm and 1.5 - 1.6×104K at 6 cm. The maximum temperature depressions appear to be associated with Hα filaments. Comparison with He 10830 Å spectroheliogram shows that 20 cm temperature depressions correspond to the region of reduced intensity in the He 10830 Å around filaments, which correspond to coronal cavities. The authors have studied the temperature and density structure of the transition sheath between the filament and the surrounding corona assuming that the energy radiated away is balanced by the energy conducted from the corona. They find that the observations can be better explained by a model having a pressure gradient in the transition sheath around the filament. Title: Microwave Observations of Red Dwarf Flare Stars Authors: Kundu, M. R.; Jackson, P. D.; White, S. M. Bibcode: 1986BAAS...18..984K Altcode: No abstract at ADS Title: Simultaneous VLA and Hard X-Ray Observations of a Large Flare on 1981 November 14 Authors: Dennis, B. R.; Kundu, M. R.; Melozzi, M. Bibcode: 1986BAAS...18..965D Altcode: No abstract at ADS Title: Solar Microbursts at Meter-Dekameter Wavelengths Authors: Kundu, M. R.; Gergely, T. E.; Szabo, A.; Loiacono, R.; White, S. M. Bibcode: 1986ApJ...308..436K Altcode: Microbursts are low-brightness-temperature bursts observed by the Clark Lake radioheliograph. The bursts occur several times per hour during quiet-sun periods and are seen at the observing frequencies from 30 to 70 MHz. They are stationary at a given frequency, have short rise times and durations of 2-10 s. Here, observations of the bursts are presented and interpretated in terms of plasma emission. The burst properties suggest that they are weak type III bursts. The observations imply that energy releases on the sun continue to be impulsive, with nonthermal electron distributions, for small releases of energy. The relation of the bursts to type III bursts and hard X-ray bursts is discussed. Title: Propagation of Weak Type III Burst Electrons in Dense Coronal Streamers Authors: Gopalswamy, N.; Kundu, M. R.; Szabo, A. Bibcode: 1986BAAS...18R.900G Altcode: No abstract at ADS Title: Book-Review - Solar Terrestrial Physics Authors: Kundu, M. R.; Biswas, S.; Reddy, B. M.; Samadurai, S.; Somov, B. V. Bibcode: 1986SSRv...44..403K Altcode: No abstract at ADS Title: A VLA Survey of dMe Flare Stars Authors: Jackson, P. D.; Kundu, M. R.; White, S. M. Bibcode: 1986BAAS...18..913J Altcode: No abstract at ADS Title: Coronal Activity at Meter-Decameter Wavelengths: Clark Lake Observations Authors: Schmahl, E. J.; Kundu, M. R.; Szabo, A.; Gergely, T. E.; Howard, R. Bibcode: 1986BAAS...18R.900S Altcode: No abstract at ADS Title: Solar Coronal Bright Points Observed with the VLA Authors: Habbal, S. R.; Ronan, R. S.; Withbroe, G. L.; Shevgaonkar, R. K.; Kundu, M. R. Bibcode: 1986ApJ...306..740H Altcode: The first observations of solar coronal bright points made at 20-cm wavelength with the VLA are reported. The brightness temperature of the sources observed varies between 1 and 5 x 10 to the 5th K. The observations indicate that significant fluctuations in the brightness temperature as well as in the spatial extent of these sources can occur over a few minutes. These fluctuations are shown to be due to density and temperature fluctuations at transition region heights combined with either plasma motions along magnetic field lines or changes in magnetic field topology, or both. Title: Book-Review - Unstable Current Systems and Plasma Instabilities in Astrophysics Authors: Kundu, M. R.; Holman, G. C.; Somov, B. V. Bibcode: 1986SSRv...44..187K Altcode: No abstract at ADS Title: A new microwave/X-ray diagnostic for the thermal phase of solar flares Authors: Schmahl, E. J.; Kundu, M. R.; Erskine, F. T. Bibcode: 1986SoPh..105...87S Altcode: We have observed 10 solar bursts during the thermal phase using the Haystack radio telescope at 22 GHz. We show that these high frequency flux observations, when compared with soft X-ray band fluxes, give useful information about the temperature profile in the flare loops. The microwave and X-ray band fluxes provide determinations of the maximum loop temperature, the total emission measure, and the index δ of the differential emission measure (q(T)/T = cTδ−1). The special case of an isothermal loop (δ = ∞) has been considered previously by Thomas et al. (1985), and we confirm their diagnostic calculations for the GOES X-ray bands, but find that the flare loops we observed departed significantly from the isothermal regime. Our results (δ = 1-3.5) imply that, during the late phases of flares, condensation cooling (δ ≈ 3.5) competes with radiative cooling (δ ≈ 1.5). Further, our results appear to be in good agreement with previous deductions from XUV rocket spectra (δ ≈ 2-3). Title: High-Spatial-Resolution Microwave and Soft X-ray Observations as Diagnostics of Solar Magnetic Loops Authors: Holman, G. D.; Webb, D. F.; Davis, J. M.; Kundu, M. R. Bibcode: 1986BAAS...18..677H Altcode: No abstract at ADS Title: Clark Lake microbursts: on a lower limit to type III burst brightnesstemperatures. Authors: White, S. M.; Kundu, M. R.; Szabo, A. Bibcode: 1986SoPh..107..135W Altcode: 1987SoPh..107..135W Further observations of solar microbursts by the Clark Lake radioheliograph are reported. The microbursts have properties consistent with weak type III bursts, with the implication that type III's can have brightness temperatures as low as 106 K. We explore the importance of this result. A single model to explain the stronger type III bursts and the weaker microbursts is sought. We show that none of the models for stabilizing the strongest type III electron streams can explain the observed microbursts: these models have threshold levels of Langmuir waves which imply emission (due to spontaneous scattering off ions) with brightness temperatures in excess of those observed. It appears that either some vital physics is still missing from models for type III bursts, or that microbursts should have properties significantly different from those of type III bursts. In the latter case further observations should allow important tests of type III models. Title: Decimeter Continuum Radio Emission from a Post-Flare Loop Authors: Kundu, M. R. Bibcode: 1986SoPh..104..223K Altcode: Radio observations offer an important means for providing estimates of magnetic fields in post-flare loops. Title: A study of hard X-ray associated meter-decameter bursts observed on December 19, 1979 Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R.; Sawant, H. S. Bibcode: 1986SoPh..103..153K Altcode: We present the results of a study of the relationship of a complex meter-decameter wavelength radio burst observed with the Clark Lake E-W and N-S interferometers, with a hard X-ray burst observed with the X-ray spectrometer aboard ISEE-3. The radio burst consisted of several type III's, reverse drift type III's, a U burst, and type II and type IV bursts. The X-ray emission was also complex. The radio as well as hard X-ray emissions were observed before the flash phase of the flare; they were not always associated and we conjecture that this may constitute evidence for acceleration of electrons high in the corona. On the other hand, all components of the reverse drift burst were associated with hard X-ray subpeaks, indicating multiple injection of electron beams along field lines with different density gradients. While the type II burst appeared to be related to the hard X-ray burst, a detailed correspondence between individual features of the radio and hard X-ray burst emissions could not be found. The type IV burst started after all hard X-ray emissions ceased. Its source appeared to be a magnetic arch, presumably containing energetic electrons responsible for the gyrosynchrotron radiation of type IV. Title: Microwave observations of red dwarf flare stars Authors: Kundu, M. R.; White, S. M.; Jackson, P. D. Bibcode: 1986AdSpR...6h.117K Altcode: 1986AdSpR...6..117K We discuss some recent observations of red dwarf flare stars. When observed over periods of about 8 hours, each of 4 flare star systems displayed at least one major flare at 20 cm. Quiescent emission at 6 cm was seen from UV Ceti and EQ Peg A, but flares were much less frequent at 6 cm than at 20 cm. We also summarize earlier observations of quiescent emission from UV Ceti. Observations of highly polarized flares with brightness temperatures in excess of 1010 K appear to be common on red dwarf stars. We have also found narrowband flares which strengthen the argument that a coheren emission mechanism is involved in these flares. One of those narrowband flares allows us to place severe constraints on conditions in the flare source, and if the flare is cyclotron maser emission it seems unlikely that magnetic reconnection is involved in the flare. Title: Shock waves and coronal transients: The event of 1980 April 17 Authors: Gary, D. E.; Gergely, T. E.; Kundu, M. R. Bibcode: 1986AdSpR...6f.311G Altcode: 1986AdSpR...6..311G The coronal mass ejection (CME) event of 1980 April 17 was observed with the SMM coronagraph, and an accompanying Type II (shock wave related) burst was observed simultaneously with the Culgoora and Clark Lake radioheliographs. The method of analysis of the combined radio observations is presented. Although the radio positions were affected by severe ionospheric refraction, the combined radio observations allow a useful reduction in the range of possible positions of the 80 MHz source when the 43 MHz source is required to lie within the range of position angles of the CME. The positions of the 80 MHz radio sources under this assumption are compared with the positions of the CME loop. Title: Simultaneous imaging and spectral observations in microwaves and hard X-rays of the impulsive phase of a solar limb flare Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R. Bibcode: 1986AdSpR...6f.143S Altcode: 1986AdSpR...6..143S We have observed the impulsive phase of a solar flare at microwave wavelengths and in hard X-rays, and deduced the strength of the magnetic field and the number of energetic electrons producing the burst. The microwave observations, using the Very Large Array at 6 cm, had spatial resolution of 8''×8'', close to the resolution of the Hard X-ray Imaging Spectrometer on SMM which also imaged this flare. The Hard X-ray Burst Spectrometer determined the spectrum of the burst in the range 25-512 keV, and several patrol telescopes recorded the microwave time profile at frequencies from 2.8 to 19.6 GHz. The combined data show that the derived number of microwave emitting electrons is at least three orders of magnitude fewer than the number of thick target electrons producing the hard X-rays. We propose that the reason for this discrepancy in numbers is that the fast electrons are highly beamed, and radiate gyrosynchrotron emission less efficiently than isotropically distributed electrons. However, we cannot rule out the alternate explanation: that the electron energy spectrum steepens at moderate energies (> 150 keV), and then flattens at higher energies (> 200 keV) where gyrosynchrotron processes become important. Title: Impulsive phase transport. Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.; Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose, D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.; Tanaka, K.; Zirin, H. Bibcode: 1986NASCP2439....3C Altcode: Contents: 1. Introduction: motivation for transport studies, historical perspective, overview of the chapter. 2. Impulsive phase observations and their interpretation: gamma-ray emission above 10 MeV, hard X-ray and microwave morphology, combined soft and hard X-ray spectra, iron Kα emission, ultraviolet and hard X-ray emission, white light emission, Hα emission. 3. Theoretical studies of transport processes: electron beams and reverse currents, proton transport, radiative energy transport by amplified decimetric waves. 4. Summary. Title: EXOSAT observations of quiescent and flaring emission from active late-type stars Authors: Pallavicini, R.; Monsignori-Fossi, B. C.; Landini, M.; Kundu, M. R.; Lang, K. R. Bibcode: 1986AdSpR...6h.125P Altcode: 1986AdSpR...6Q.125P The authors present the highlights of several guest investigator programs carried out with the EXOSAT satellite. They discuss quiescent as well as flaring emission from normal F to M dwarfs, from dMe flare stars and from RS CVn binaries. Title: Solar-terrestrial physics. Proceedings of the second Indo-US workshopon solar-terrestrial physics, held at New Delhi, India, 30 January - 3 February 1984. Authors: Kundu, M. R.; Biswas, S.; Reddy, B. M.; Samadurai, S. Bibcode: 1986spps.book.....K Altcode: No abstract at ADS Title: Possible evidence for beaming in flares from microwave and hard X-rayimaging and spectra. Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R. Bibcode: 1986lasf.conf..396S Altcode: 1986lasf.symp..396S The authors have observed the impulsive phase of a solar flare at microwave wavelengths and in hard X-rays, and deduced the strength of the magnetic field and the number of energetic electrons producing the burst. The combined data show that the derived number of microwave emitting electrons is at least three orders of magnitude fewer than the number of thick target electrons producing the hard X-rays. The authors propose that the reason for this discrepancy in numbers is that the fast electrons are highly beamed, and radiate gyrosynchrotron emission less efficiently than isotropically distributed electrons. Title: A high spatial resolution study of microwave flare precursors Authors: Kundu, M. R. Bibcode: 1986AdSpR...6f..93K Altcode: 1986AdSpR...6...93K We provide several examples of preflare changes from VLA high resolution microwave data, which show that in general the active region increases in intensity and polarization over a period of several tens of minutes prior to the onset of a flare in that region. However, this phenomenon by itself does not appear to be sufficient to trigger a flare. We show that a few minutes (<~ 10 min) just before the flare onset something else happens, usually in the form of one of the following three features: (1) sudden change of polarization of the flaring region; (2) change of orientation of the neutral plane separating one polarity from another in a bipolar region; and (3) appearance of new sources in the immediate vicinity of some pre-existing structure of the active region. All three features are consistent with the emergence of new flux, which interacts with a pre-existing region to form a neutral or current sheet. The formation of the latter is ultimately responsible for triggering the onset of a flare. Title: Coronal activity at radio wavelengths. Authors: Kundu, M. R. Bibcode: 1986HiA.....7..725K Altcode: The author describes the multifrequency radioheliograph of the Clark Lake Radio Observatory. Its use for studies of large scale structures of the corona at long radio wavelengths is discussed. The author shows that features corresponding to coronal streamers and coronal holes are readily apparent in the Clark Lake maps. The author also presents results on studies of microbursts at meter-decameter wavelengths. Title: Microwave Observations of Flare Stars UV Ceti, AT Mic, and AU Mic Authors: Kundu, M. R.; Jackson, P. D.; Melozzi, M.; White, S. M. Bibcode: 1986LNP...254..284K Altcode: 1986csss....4..284K No abstract at ADS Title: EXOSAT Detection of a Very Large Flare on EQ Peg Authors: Pallavicini, R.; Kundu, M. R.; Jackson, P. D. Bibcode: 1986LNP...254..225P Altcode: 1986csss....4..225P No abstract at ADS Title: Microbursts observed at Clark Lake Authors: White, S. M.; Kundu, M. R.; Gergely, T. E. Bibcode: 1986AdSpR...6f.285W Altcode: 1986AdSpR...6Q.285W Microbursts are low brightness temperature burst observed by the Clark Lake radioheliograph. The bursts are seen at the observing frequencies from 30 MHz to 70 MHz, are stationary at a given frequency, and have short rise times and durations of 2 - 10 seconds. We present observations of the bursts, and show that their properties imply that they are weak type III bursts. However, we also show that none of the theories invoked to explain strong type III bursts can accomodate such weak bursts. We expect that important differences in the properties of microbursts and the stronger type III's will be found, and will be important in understanding the propagation of electron streams in the corona. Title: Particle acceleration. Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.; Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.; Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.; Tsuneta, S.; van Hoven, G. Bibcode: 1986NASCP2439....2V Altcode: Contents: 1. Introduction. 2. Phenomena associated with mildly-relativistic electrons: soft and hard X-ray source structure, location and development, microwave source structure, location and development, time structures and time delays in radio and hard X-rays, microwave rich flares, decimetric - metric observations and comparison with X-ray observations, discussion of models for X-ray and microwave emission. 3. Phenomena associated with ions and relativistic electrons: gamma-ray observations, neutron observations, implications of gamma-ray and neutron observations, interplanetary charged-particle observations, acceleration mechanisms. 4. Mechanisms for particle acceleration in flares: particle acceleration in reconnecting magnetic fields, electron acceleration along the magnetic field with sub-Dreicer electric fields, lower hybrid waves, Fermi acceleration and MHD turbulence, shock acceleration, acceleration of electrons by intense radio waves, preferential acceleration of heavy ions. 5. Achievements - outstanding questions. Title: Impulsive energy release in solar flares: A summary Authors: Kundu, M. R. Bibcode: 1986AdSpR...6f.207K Altcode: 1986AdSpR...6..207K Discoveries in solar physics made during the SMM-SMY-SMA period are highlighted, with special reference to impulsive energy release in solar flares. Major discoveries include observational evidence for magnetic reconnection and its theoretical interpretation, chromospheric evaporation to explain the simultaneous blue shift of X-ray lines and red shift of Hα, simultaneous production of high energy (Mev) electrons and protons, and their acceleration by Fermi shock acceleration upto 100 Mev energies, and evidence for a new acceleration process to explain the electron deficient very hard ion spectrum ( > 1000 Mev) in the extended emission phase of the large 1982 June 3 flare. Title: High Spatial Resolution Microwave Observations of Solar Flares Authors: Kundu, M. R. Bibcode: 1986spps.book..159K Altcode: No abstract at ADS Title: The proposed NRAO Millimeter Array and its use for solar studies. Authors: Kundu, Mukul R. Bibcode: 1986NASCP2449..471K Altcode: 1986rfsf.nasa..471K The author gives a brief summary of the proposed NRAO Millimeter Array discussed at a workshop held in Green Bank, W. Va., September 30 - October 2, 1985. He also provides a brief description of the solar studies that can be made with such an array. Title: Microwave imaging of a solar limb flare - Comparison of spectra and spatial geometry with hard X-rays Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R. Bibcode: 1985ApJ...299.1017S Altcode: A solar limb flare was mapped using the Very Large Array (VLA) together with hard X-ray (HXR) spectral and spatial observations of the Solar Maximum Mission satellite. Microwave flux records from 2.8 to 19.6 GHz were instrumental in determining the burst spectrum, which has a maximum at 10 GHz. The flux spectrum and area of the burst sources were used to determine the number of electrons producing gyrosynchrotron emission, magnetic field strength, and the energy distribution of gyrosynchrotron-emitting electrons. Applying the thick target model to the HXR spectrum, the number of high energy electrons responsible for the X-ray bursts was found to be 10 to the 36th, and the electron energy distribution was approximately E exp -5, significantly different from the parameters derived from the microwave observations. The HXR imaging observations exhibit some similiarities in size and structure o the first two burst sources mapped with the VLA. However, during the initial burst, the HXR source was single and lower in the corona than the double 6 cm source. The observations are explained in terms of a single loop with an isotropic high-energy electron distribution which produced the microwaves, and a larger beamed component which produced the HXR at the feet of the loop. Title: Book-Review - Unstable Current Systems and Plasma Instabilities in Astrophysics - I.A.U. SYMP.107 Authors: Kundu, M. R.; Holman, G. D.; Roberts, B. Bibcode: 1985Obs...105..240K Altcode: No abstract at ADS Title: Simultaneous observations of hard X-ray and microwave burst sources in a limb flare Authors: Takakura, T.; Kundu, M. R.; McConnell, D.; Ohki, K. Bibcode: 1985ApJ...298..431T Altcode: Associated with a flare that occurred just behind the west solar limb on 1981 August 3, a hard X-ray source (20 - 30 keV) and a microwave source at 5 GHz were observed simultaneously with the Hinotori spacecraft and the VLA. Both sources were located in the corona. The height of the centroid above the west limb was 15arcsec (104km) for the hard X-ray source and 54arcsec (4×104km) for the radio source. The sources are believed to be located near the tops of two independent coronal arcades or loops, one low and the other high, rather than at two different heights of a common arcade or loop. Title: Microwave emission from late-type dwarf stars UV Ceti and YZ Canis Minoris. Authors: Kundu, M. R.; Shevgaonkar, R. K. Bibcode: 1985ApJ...297..644K Altcode: Simultaneous high-resolution observations of two late-type dwarf stars, UV Cet and YZ CMi, at 6 and 20 cm are presented. These observations put sufficient constraints on existing interpretations to conclude that the quiescent microwave emission from these stars is due to gyrosynchrotron radiation of nonthermal electrons having a power-law energy distribution. From the lifetime of 1 hr of the nonthermal particles against radiation and collision losses, a magnetic field of a few thousand gauss on the photosphere of these stars is estimated. The observations indicate that the ambient density in the coronae of YZ CMi is an order of magnitude higher than that of UV Cet. Title: High Spatial Resolution Microwave Observations of the Sun Authors: Kundu, M. R. Bibcode: 1985SoPh..100..491K Altcode: Over the past decade two large arrays — the Westerbork Synthesis Radio Telescope (WSRT) and the Very Large Array (VLA) built primarily for sidereal radio astronomy have been used for solar radio astronomical studies with spatial resolution of a few seconds of arc. In this review, we discuss some results obtained at Maryland using these instruments. Title: The Diameter of the Sun at Decameter Wavelengths Authors: Gergely, T. E.; Gross, B. D.; Kundu, M. R. Bibcode: 1985SoPh...99..323G Altcode: Using observations obtained with the Clark Lake radioheliograph we determined the diameter of the Sun in the decameter wavelength range. Both equatorial and polar diameters increase with decreasing frequency, as D=Afα. The eccentricity of the brightness distribution appears to remain constant in the frequency range (30-74 MHz) in good agreement with the optical results in a corresponding height range. The smaller size of the polar diameter is attributed to coronal holes covering the poles during the period of our observations, while streamers were observed at the equator most of the time. Title: Book-Review - Unstable Current Systems and Plasma Instabilities in Astrophysics Authors: Kundu, M. R.; Holman, G. D. Bibcode: 1985S&T....70..134K Altcode: No abstract at ADS Title: Book-Review - Unstable Current Systems and Plasma Instabilities in Astrophysics Authors: Kundu, M. R.; Holman, G. D.; Kleczek, J. Bibcode: 1985Ap&SS.113..424K Altcode: No abstract at ADS Title: VLA Observations of a Radio Plage at Centimeter Wavelengths Authors: Shevgaonkar, R. K.; Kundu, M. R. Bibcode: 1985SoPh...98..119S Altcode: VLA observations of a solar plage region at 6 and 20 cm wavelengths are presented. The high frequency 6 cm emission correlates well with the associated sunspots, whereas 20 cm emission shows good correlation with the Hα plage. Large temperature variations over a period of one day are observed in the plage associated component without any significant changes in the sunspots. The dominant emission mechanisms at 6 and 20 cm are found to be gyroresonance radiation and bremstrahlung respectively. It is concluded that the coronal condensation above the chromospheric Hα plage has an electron density of ∼5 × 109 cm−3 and it extends to a height of ∼5 × 104 km. Title: Book-Review - Unstable Current Systems and Plasma Instabilities in Astrophysics Authors: Kundu, M. R.; Holman, G. D. Bibcode: 1985Sci...229...46K Altcode: No abstract at ADS Title: Microwave Emission from Late Type Dwarf Stars UV Ceti and YZ CMi Authors: Kundu, M. R.; Shevgaonkar, R. K. Bibcode: 1985ASSL..116..229K Altcode: 1985rst..conf..229K The authors present simultaneous VLA observations of two late type dwarf stars UV Ceti and YZ CMi at 6 and 20 cm. Multiwavelength observations put sufficient constraints on existing interpretations of quiescent radio emission from these stars. They found that the microwave emission is due to gyro-synchrotron radiation of nonthermal electrons having a power law energy distribution. This emission originates from a source whose size is 2 - 3 times larger than the star. The authors estimate a magnetic field of ≡140 G and a density of ⪉2×108cm-3 in the microwave source. Title: Summary of the Current and Future Problems in Radio Stars Authors: Kundu, M. R.; Hjellming, R. M. Bibcode: 1985ASSL..116..397K Altcode: 1985rst..conf..397K No abstract at ADS Title: Simultaneous Microwave Observations of Solar Flares at 6-CM and 20-CM Wavelengths Using the VLA Authors: Melozzi, M.; Kundu, M. R.; Shevgaonkar, R. K. Bibcode: 1985SoPh...97..345M Altcode: Using the Very Large Array, solar burst observations have been carried out simultaneously at 6 and 20 cm. Structural changes and preheating have been observed in the flaring regions on time scales of minutes to tens of minutes before the onset of the burst impulsive phase. The 6 cm burst sources are located close to the neutral line, or near the legs of a flaring loop. The 20 cm burst sources show complex and extended structures spatially separated from both the preburst emission and the gradual decay phase of the burst. We interpret the observations in terms of a two-component flare model (bulk heating as well as acceleration of particles) and derive the physical parameters of the burst sources. Title: Book-Review - Unstable Current Systems and Plasma Instabilities in Astrophysics Authors: Kundu, M. R.; Holman, G. D.; Achterberg, A. Bibcode: 1985SSRv...41..212K Altcode: No abstract at ADS Title: Erratum - a Study of Flare Buildup from Simultaneous Observations in Microwave Hα and Ultraviolet Wavelengths Authors: Kundu, M. R.; Gaizauskas, V.; Woodgate, B. E.; Schmahl, E. J.; Shine, R.; Jones, H. P. Bibcode: 1985ApJS...58..195K Altcode: No abstract at ADS Title: The microwave structure of hot coronal loops Authors: Holman, G. D.; Kundu, M. R. Bibcode: 1985ApJ...292..291H Altcode: The thermal cyclotron emission from model dipole magnetic loops is computed. It is shown that a simple, isothermal dipole loop can show a great deal of spatial and polarization structure at microwave frequencies. This structure is sensitive to the observation frequency and angle of observation. Two qualitatively distinct microwave loop structures can be distinguished: (1) 'thin loop,' observed as a string of independent microwave peaks, corresponding to different harmonics of the local electron gyrofrequency; and (2) 'thick loop,' the harmonics are merged, so that a more continuous microwave structure is observed. It is shown that the presence of an external plasma can result in a change in the observed mode of polarization along one leg of a loop, without a change in the sign of the line-of-sight magnetic field. Models such as these, along with high-resolution microwave and related observations, can provide an excellent diagnostic of the magnetic and plasma properties of coronal loops. Title: Dual frequency observations of solar microwave bursts using the VLA Authors: Shevgaonkar, R. K.; Kundu, M. R. Bibcode: 1985ApJ...292..733S Altcode: Simultaneous observations at 2 and 6 cm wavelengths of a solar active region and of microwave bursts were carried out with the VLA. The quiescent 6 cm emission is strongly associated with photospheric sunspots and is dominated by gyroresonance radiation. The emission at 2 cm, on the other hand, is due to free-free mechanism, and it originates from the chromosphere-corona transition region. The bursts observed have multiple peaks. Two-dimensional snapshot maps have been produced at 6 and 2 cm. From the brightness temperature and the degree of circular polarization, the magnetic field in the microwave burst sources has been estimated. The generating mechanisms responsible for 6 and 2 cm radiation are discussed; it is concluded that the 6 cm radiation in the bursts studied here originates from the bulk heated plasma, whereas the 2 cm radiation is due to the nonthermal particles generated in the energy-release process. Title: Multiwavelength observations of a preflare solar active region using the VLA Authors: Kundu, M. R.; Shevgaonkar, R. K. Bibcode: 1985ApJ...291..860K Altcode: A preflare active region was studied using the Very Large Array at 2, 6, and 20 cm. At 2 cm the region is composed of two components located in regions of opposite polarity. Both components are preheated prior to the impulsive onset of a flare. However, one component develops new structures during preburst phase, and the burst occurs in this location. It is believed that the new structures represent emerging flux regions which interact with an overlying loop to produce a neutral sheet, which ultimately is responsible for triggering the flare. Title: The Sun and nearby Stars: Microwave Observations at High Resolution Authors: Kundu, M. R.; Lang, K. R. Bibcode: 1985Sci...228....9K Altcode: High-resolution microwave observations are providing new insights into the nature of active regions and eruptions on the sun and nearby stars. The strength, evolution, and structure of magnetic fields in coronal loops can be determined by multiple-wavelength observations with the Very Large Array. Flare models can be tested with Very Large Array snapshot maps, which have angular resolutions of better than 1 second of arc in time periods as short as 10 seconds. Magnetic changes that precede solar eruptions on time scales of tens of minutes involve primarily emerging coronal loops and the interactions of two or more loops. Magnetic reconnection at the interface of two closed loops may accelerate electrons and trigger the release of microwave energy in the coronal parts of the magnetic loops. Nearby main-sequence stars of late spectral type emit slowly varying microwave radiation and stellar microwave bursts that show striking similarities to those of the sun. Title: Book-Review - Unstable Current Systems and Plasma Instabilities in Astrophysics Authors: Kundu, M. R.; Holman, G. D. Bibcode: 1985JBAA...95..139K Altcode: No abstract at ADS Title: Observations of the Cygnus Loop at 40 MHz with the Clark Lake Teepee Tee Authors: Jackson, P. D.; Kassim, N. E.; Kundu, M. R. Bibcode: 1985BAAS...17..545J Altcode: No abstract at ADS Title: Observations of Flares at 6 and 20 cm Wavelengths From Late Type Dwarf Stars UV Ceti and AT Mic Authors: Kundu, M. R.; Jackson, P. D.; Melozzi, M. Bibcode: 1985BAAS...17..589K Altcode: No abstract at ADS Title: A study of flare buildup from simultaneous observations in microwave, H-alpha, and UV wavelengths Authors: Kundu, M. R.; Gaizauskas, V.; Woodgate, B. E.; Schmahl, E. J.; Shine, R.; Jones, H. P. Bibcode: 1985ApJS...57..621K Altcode: The results of high-resolution observations of the solar preflare activity of June 25, 1980 are analyzed. The observations were carried out simultaneously in the UV microwave, and H-alpha wavelengths using the VLA, the Ottawa River photoheliograph, and the Solar Max spectrometer and polarimeter instruments. Increases were observed in the intensitiy and polarization of compact sources at a wavelength of 6-cm during the preflare hour. The increases were associated with rising and twisting motions in the magnetic loops near the sight of the subsequent flare. Consistent with this process, analysis of the transverse and Doppler motions observed in the H-alpha filament before disruption showed that the filament was activated internally by the motions of evolving magnetic flux patterns. Ultraviolet data for C IV brightenings and upflows at the first appearance of the H-alpha filament indicated the presence of rising magnetic loops and material rising within the loops. The complete VLA, microwave and H-alpha data sets are given. Title: The coalescence instability in solar flares Authors: Tajima, T.; Brunel, F.; Sakai, J. -I.; Vlahos, L.; Kundu, M. R. Bibcode: 1985IAUS..107..197T Altcode: The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic and emission as well as the characteristics of two-dimensional microwave images obtained during a flare. The plasma compressibility leads to the explosive phase of loop coalescence and its overshoot results in amplitude oscillations in temperatures by adiabatic compression and decompression. It is noted that the presence of strong electric fields and super-Alfvenic flows during the course of the instability play an important role in the production of nonthermal particles. A qualitative explanation on the physical processes taking place during the nonlinear stages of the instability is given. Title: Unstable current sytems and plasma instabilities in astrophysics Authors: Kundu, M. R.; Holman, G. D. Bibcode: 1985IAUS..107.....K Altcode: Among the topics discussed are: magnetic field reconnection in cosmic plasmas; energy dissipation mechanisms in the solar corona; and the acceleration of runaway electrons and Joule heating in solar flares. Consideration is also given to: the nonlinear evolution of the resistive tearing mode; anomalous transport in current sheets; equilibrium and instability in extragalactic jets; and magnetic field reconnection in differentially rotating accretion disks. Among additional topics discussed are: the creation of high energy electron tails by lower hybrid waves and its connection with type-II and type-III bursts; beam current systems in solar flares; and the spatio-temporal features of microwave emissions of active regions and flares. Title: Forty Years of Solar Radio Research Authors: Kundu, M. R. Bibcode: 1985spit.conf...23K Altcode: No abstract at ADS Title: Microwave Observations of Solar Active Regions and Flares Using the Very Large Array Authors: Kundu, M. R. Bibcode: 1985spit.conf..503K Altcode: No abstract at ADS Title: An interpretation of the millisecond time variation in hard X-ray solar flares Authors: Krishan, V.; Kundu, M. R. Bibcode: 1985IAUS..107..299K Altcode: Recent observations of the fast time variability in the hard X-ray emission from solar flares are interpreted. The fast spikes are assumed to be superimposed on the thermal X-ray emission. The rise and fall of a spike are caused by disruptions in the plasma. The rise time represents the impulsive heating time and the decay or fall time represents a quick cooling of the plasma due to the accelerating growth rate of the m = 1 tearing mode. The estimated characteristic time durations of the spike are found to be in good agreement with the observed ones. Title: Observational evidence for magnetic reconnection in microwave solar bursts Authors: Kundu, M. R. Bibcode: 1985IAUS..107..185K Altcode: Observations of magnetic reconnection in the solar coronal magnetic field are presented. The observations were carried out using the NRAO VLA with a special resolution of 2 arcsec at 6-cm. The period of observation corresponded to the onset of an impulsive burst observed on May 14, 1980 at 19:57 UT. A second set of VLA observations of several interconnecting coronal loops associated with the onset of an impulsive burst on June 24, 1980, is also presented. The acceleration of electrons emitting microwaves was observed during magnetic reconnection in both events. Polarization maps for three selected phases in the evolution of the burst events are provided. Title: Erratum - Microwave Soft and Hard X-Ray Imaging Observations of Two Solar Flares Authors: Kundu, M. R.; Machado, M. E.; Erskine, F. T.; Rovira, M. G.; Schmahl, E. J. Bibcode: 1984A&A...140..476K Altcode: No abstract at ADS Title: Center-to-limb variation of a sunspot-associated microwave source Authors: Alissandrakis, C. E.; Kundu, M. R. Bibcode: 1984A&A...139..271A Altcode: Observations of the simple bipolar active region McMath 16862, obtained with the Westerbork Synthesis Radio Telescope at 6.16 cm over six consecutive days, indicate two bright sources associated with the region's two main spots, as well as some weaker emission that may be associated with loop structures. Application of a novel analytical method has allowed the mapping of the vertical as well as the horizontal component of the sunspot magnetic field at specific locations in the low corona. While the vertical component decreases away from the source's center, the horizontal component has both a radial and an azimuthal part. These results are interpreted in terms of a force-free magnetic field model, as well as in terms of a dipole whose axis is inclined to the vertical. Title: Microwave Emission from Late Type Dwarf Stars UV Ceti and YZ CMi Authors: Kundu, M. R.; Shevgaonkar, R. K. Bibcode: 1984BAAS...16Q.892K Altcode: 1984BAAS...16..892K No abstract at ADS Title: Structure and Polarization of Active Region Microwave Emission Authors: Kundu, M. R.; Alissandrakis, C. E. Bibcode: 1984SoPh...94..249K Altcode: We present observations of active region radio emission at 6.16 cm wavelength, obtained with an angular resolution of 3″ by 10″ arc using the Westerbork Synthesis Radio Telescope (WSRT) during the action interval May 20-27, 1980 of the Solar Maximum Year (SMY). We present maps in both total intensity (I) and circular polarization (V) of three regions (Hale numbers 16850, 16863, and 16864) and provide a detailed comparison of these maps with on- and off-band Hα pictures and with magnetograms. The strongest sources were associated with neutral lines and soft X-ray arcades. We present evidence that these neutral lines were characterized by having their two opposite polarities close to each other, implying a high magnetic field gradient, and by their association with arch filament systems. The sunspot associated radio sources had a relatively simple structure in region 16850; however for the large spots of regions 16864 and 16863 the emission had a patchy appearance with a tendency of the peaks to lie over the penumbra. In the V maps we observed for the first time two `islands', polarized in the sense of the ordinary mode, which were located inside the sunspot associated sources and were associated with intrusions of opposite polarity field into the penumbra. These structures can be accounted for if the electron temperature along the line of sight is not a monotonically increasing function of height, but has a maximum near the second harmonic level. Finally we give a detailed analysis of observations of the inversion of the sense of circular polarization in region 16863. We find that the large scale structure of the magnetic field can be approximated by a dipole with its axis inclined by 11° with respect to the photosphere and with a dipole moment of about 2 × 1031 cgs units; the depolarization line is located at a height of 0.16-0.19 R⊙ above the dipole, where the estimated intensity of the magnetic field is 10-20 G. Title: Simultaneous Observations of Solar Flares at 6 and 20 cm Wavelengths Using the VLA Authors: Melozzi, M.; Shevgaonkar, R. K.; Kundu, M. R. Bibcode: 1984BAAS...16.1003M Altcode: No abstract at ADS Title: Microbursts at Meter-Decameter Wavelengths Authors: Kundu, M. R.; Gergely, T. E.; Loiacono, R. Bibcode: 1984BAAS...16R.892K Altcode: No abstract at ADS Title: Temporal and Spatial Variations of Solar Coronal Bright Points Observed with the VLA Authors: Habbal, S. R.; Cowell, A.; Ronan, R.; Withbroe, G. L.; Shevgaonkar, R.; Kundu, M. Bibcode: 1984BAAS...16..929H Altcode: No abstract at ADS Title: Microwave and Hard X-ray Imaging of a Solar Limb Flare Authors: Schmahl, E. J.; Kundu, M. R. Bibcode: 1984BAAS...16.1002S Altcode: No abstract at ADS Title: Coronal extension of flaring region magnetic fields inferred from high-resolution microwave and type III burst observations Authors: Lantos, P.; Pick, M.; Kundu, M. R. Bibcode: 1984ApJ...283L..71L Altcode: Observations of three solar radio bursts, obtained with the Very Large Array of the National Radio Astronomy Observatory at 6 cm wavelength, have been combined with meter observations from the Mark III Nancay Radioheliograph. There is a good correlation between solar activity observed at the two wavelength domains. A small change by about 10 sec in the centimetric burst location corresponds to a large change, by about 0.5 solar radius, in the related metric type III burst location. This indicates discrete injection/acceleration regions and the presence of very divergent magnetic fields. The bursts come from two distinct active regions. With two-dimensional spatial resolution, it is shown that, in this sample, each active region possesses a coronal extension that is separated from that of the neighboring active region. Title: Three-dimensional structures of two solar active regions from VLA observations at 2, 6, and 20 centimeter wavelengths Authors: Shevgaonkar, R. K.; Kundu, M. R. Bibcode: 1984ApJ...283..413S Altcode: Three-dimensional structures of two active region groups are determined from observations with the Very Large Array (VLA) at 2, 6, and 20 cm. One of the groups exhibits a single magnetic loop of length approximately 10 to the 10th cm. The 2 cm radiation is mostly thermal bremsstrahlung and originates from the footprints of the loop. The 6 and 20 cm radiation is dominated by low-harmonic gyroresonance radiation and originates from the upper portion of the legs or the top of the loop. The loop broadens toward the apex. The top of the loop is not found to be the hottest point, but two temperature maxima on either side of the loop apex are observed, which is consistent with the model proposed for long loops. From 2 and 6 cm observations it can be concluded that the electron density and temperature cannot be uniform in a plane perpendicular to the axis of the loop; the density should decrease away from the axis of the loop. Title: Recent advances in solar radio physics Authors: Kundu, M. R. Bibcode: 1984InEPS..93..201K Altcode: High spatial resolution microwave observations of solar active regions, coronal loops and flares are reviewed. Observations of preflare active regions are presented; in particular the interpretations of reversal of polarization at the flare site and the role of newly emerging flux in triggering the onset of flares are considered. The spatial locations of microwave burst emitting regions are discussed; loops or arcades of loops appear to be the sites of flare energy release in microwave bursts. Direct observational evidence of magnetic reconnection as the primary cause of acceleration of electrons in microwave bursts is provided. Title: Sharp Edges in Solar Microwave Spectra - Neutral Current Sheets or Cyclotron Lines Authors: Schmahl, E. J.; Shevgaonkar, R. K.; Kundu, M. R.; McConnell, D. Bibcode: 1984SoPh...93..305S Altcode: We have mapped two solar active regions using the VLA at three closely spaced frequencies (4496, 4716, and 4996 MHz) in an attempt to determine the origin of the steep spectra (indexγ ≈ −5 to −8) sometimes observed with large single telescopes. One of the regions observed indeed shows an anomalously large slope (γ ≈ −6) compared to the usual (γ ≈ −2 to −2.5). The other region shows a similar slope (γ ≈ −5) but with a larger range of statistical error. Two possible explanations for such steep edges in solar spectra are (1) transmission effects of neutral current sheets, and (2) the appearance of cyclotron lines. The internal evidence of the microwave maps and simultaneous optical observations favor an explanation in terms of cyclotron lines. Title: The Radio Sky from Clark Lake Authors: Kundu, M. R. Bibcode: 1984S&T....67..519K Altcode: The Clark Lake Radio Observatory's telescope is currently the most sophisticated instrument for low frequency astronomical radio research. Using this instrument, astronomers have identified an association of bright X-ray point flares on the sun with the brief, intense radio bursts, classified as 'Type III', that are generated by the interaction of electron streams with ambient coronal plasma. Other solar observations at Clark Lake are of coronal transient shock waves and plasma cloud distributions. Radio galaxies such as 3C 129 are also frequent objects of study. Title: The spatial distribution of 6 centimeter gyroresonance emission from a flaring X-ray loop Authors: Kahler, S. W.; Webb, D. F.; Davis, J. M.; Kundu, M. R. Bibcode: 1984SoPh...92..271K Altcode: We compare simultaneous high resolution soft X-ray and 6 cm images of the decay phase of an M3 X-ray flare in Hale Region 16413. The photographic X-ray images were obtained on an AS & E sounding rocket flown 7 November, 1979, and the 6 cm observations were made with the VLA. The X-ray images were converted to arrays of line-of-sight emission integrals and average temperature throughout the region. The X-ray flare structure consisted of a large loop system of length ∼ 1.3 arc min and average temperature ∼8 × 106 K. The peak 6 cm emission appeared to come from a region below the X-ray loop. The predicted 6 cm flux due to thermal bremsstrahlung calculated on the basis of the X-ray parameters along the loop was about an order of magnitude less than observed. We model the loop geometry to examine the expected gyroresonance absorption along the loop. We find that thermal gyroresonance emission requiring rather large azimuthal or radial field components, or nonthermal gyrosynchrotron emission involving continual acceleration of electrons can explain the observations. However, we cannot choose between these possibilities because of our poor knowledge of the loop magnetic field. Title: VLA observations of fine structures in a solar active region at 6 centimeter wavelength. Authors: McConnell, D.; Kundu, M. R. Bibcode: 1984ApJ...279..421M Altcode: A complex solar active region at 6 cm has been observed with the VLA. Radio images of the region have been constructed and compared with simultaneous optical data from the region. It is found that all radio sources are associated with either sunspots or regions of the corona where strong transverse magnetic fields are likely, that the transverse field sources are brighter than the sunspot sources, and that some of the sunspot sources have a polarized ring structure. The observations are interpreted in terms of thermal gyroresonance emission, with the radiation from the transverse field sources being at the third harmonic of the gyrofrequency and predominantly at the second harmonic from the sunspot sources. Title: Sharp Edges in Solar Microwave Spectra: Neutral Current Sheets or Cyclotron Lines? Authors: Schmahl, E. J.; Shevgaonkar, R. K.; Kundu, M. R. Bibcode: 1984BAAS...16..534S Altcode: No abstract at ADS Title: Simultaneous Observation of Hard X-ray and Microwave Burst Sources in a Limb Flare Authors: Kundu, M. R.; Takakura, T. Bibcode: 1984BAAS...16..524K Altcode: No abstract at ADS Title: Microwave, soft and hard X-ray imaging observations of two solar flares Authors: Kundu, M. R.; Machado, M. E.; Erskine, F. T.; Rovira, M. G.; Schmahl, E. J. Bibcode: 1984A&A...132..241K Altcode: A set of microwave and hard X-ray observations of two flares observed simultaneously with the Very Large Array (VLA) and the Solar Maximum Mission Hard X-ray Imaging Spectrometer (SMM-HXIS) are presented. The LVA was used at 6 cm to map the slowly varying and burst components in three neighboring solar active regions (Boulder Nos. 2522, 2530, and 2519) from approximately 14:00 UT until 01:00 UT on June 24-25, 1980. Six microwave bursts less than 30 sfu were observed, and for the strongest of these, two-dimensional 'snapshot' (10 s) maps with spatial resolution of 5 in. were synthesized. HXIS data show clear interconnections between regions 2522 and 2530. The X-ray observations present a global picture of flaring activity, while the VLA data show the complexity of the small magnetic structures associated with the impulsive phase phenomena. It is seen that energy release did not occur in a single isolated magnetic structure, but over a large area of intermingled loop structures. Title: The Microwave Structure of Hot Coronal Loops Authors: Holman, G. D.; Kundu, M. R.; Yang, C. Bibcode: 1984BAAS...16R.534H Altcode: No abstract at ADS Title: Simultaneous Dual Wavelength Observations of an Impulsive Microwave Burst Using the VLA Authors: Shevgaonkar, R. K.; Kundu, M. R. Bibcode: 1984BAAS...16Q.524S Altcode: No abstract at ADS Title: Interpretation of microwave active region structures using SMM soft X-ray observations Authors: Strong, K. T.; Alissandrakis, C. E.; Kundu, M. R. Bibcode: 1984ApJ...277..865S Altcode: The purpose of this paper is to investigate the roles played by the geometrical effect of gyroresonance absorption and by the low-temperature (<106K) flux tubes above sunspot regions with microwave ring structures, by combining WSRT 6 cm observations with the X-ray observations made with the X-ray Polychromator on the SMM satellite. Some features associated with Hale regions 16863 and 16864 are analyzed from observations on 1980 May 25 and 26 combined with model computations of the radio emission. The nature of a cool and compact coronal feature seen in soft X-rays, which corresponded to some interesting microwave and magnetic features, is also examined. Finally, the origin of the X-ray and radio emission associated with neutral lines of the magnetic field is considered. Title: A study of the evolution of energetic electrons in a solar flare Authors: Holman, G. D.; Kundu, M. R.; Dennis, B. R. Bibcode: 1984ApJ...276..761H Altcode: A study of the impulsive microwave and hard X-ray emissions from the June 25, 1980 solar flare notes that its light curves are consistent with the flaring of the regions in unison rather than sequentially, or in an uncorrelated manner. The maximum 6-cm flux, which occurs 1.4 min after the maximum in the integrated 28-498 keV X-ray emission, and coincides with a secondary peak in the X-ray light curve, is explained by the observation that the X-ray spectrum, and hence that of the electrons, is harder at the time of the 6-cm flux maximum. The results show a clear correlation between the X-ray flux greater than 100 keV and the microwave flux. The steep, low-frequency spectrum at the time of the 6-cm maximum indicates that the emission at this time is nonthermal. The spectral behavior of the hard X-ray emission is not consistent with the betatron acceleration mechanism. Title: A multiple type-II burst associated with a coronal transient and its MHD simulation Authors: Gergely, T. E.; Kundu, M. R.; Wu, S. T.; Dryer, M.; Smith, Z.; Stewart, R. T. Bibcode: 1984AdSpR...4g.283G Altcode: 1984AdSpR...4..283G A large coronal transient took place on 8 May 1981. The transient was related to an M7.7/2B flare and was associated with at least two coronal type II bursts. The velocities of the type II bursts were in the range 1100-1800 kms-1, in excess of the transient velocity of 500-1000 kms-1. Two dimensional positions of the type II radio sources are available from both the Clark Lake and the Culgoora Radio Observatories. We carry out two dimensional MHD simulations of the event, taking into account the observed velocity, position, and size of the type II bursts. We simulate the multiple shocks observed during the event and their interaction, and discuss some results of the simulation. Title: Coronal transients and their interplanetary effects. Authors: Hundhausen, A. J.; Burlaga, L. F.; Feldman, W. C.; Gosling, J. T.; Hildner, E.; House, L. L.; Howard, R. A.; Krieger, A. S.; Kundu, M. R.; Low, B. C.; Sheeley, N. R., Jr.; Steinolfson, R. S.; Stewart, R. T.; Stone, R. G.; Wu, S. T. Bibcode: 1984NASRP1120....6H Altcode: Contents: 1. Introduction. 2. Background material: Ancient history - solar flares and geomagnetic storms. Modern history - interplanetary shock waves. Coronal transients or mass ejections. 3. The present: Theoretical models. New observations of coronal mass ejections. 4. The future: Solar origins. Interplanetary effects. Title: Forty Years of Solar Radio Astronomy - a History of Major Advances Authors: Kundu, Mukul R. Bibcode: 1984sdra.conf..247K Altcode: 1983sdra.conf..247K No abstract at ADS Title: Observations of solar radio bursts from meter to kilometer wavelengths Authors: Kundu, M. R.; Stone, R. G. Bibcode: 1984AdSpR...4g.261K Altcode: 1984AdSpR...4..261K Using the Clark Lake Radioheliograph data we present direct evidence that type III electron streams propagate in dense coronal streamers. We also present imaging observations of meter-decameter microbursts, which appear to be similar to those observed in hard X-rays. At meter-decameter wavelengths, these microbursts appear to be due to plasma radiation. From observations made with ISSE-3, we discuss the characteristics of hectometer and kilometer wavelength radio bursts. In particular, we show that from studies of type III storms that the exciter electrons propagate along spiral structures, where the density is enhanced and that there is an acceleration of the solar wind. We discuss type II bursts at kilometer wavelengths, compare them with meter type II bursts and discuss their association with interplanetary shocks. We show that the interaction between type III electron streams and shocks at kilometer wavelengths can provide information on the interplanetary shock geometry. Finally, we discuss the possibility that some shock associated (SA) events may be emissions caused by electrons accelerated lower in the atmosphere rather than high in the corona in type II shocks.

Recent advances in solar research have resulted from new work on plasma radiation theory, new observations of active regions and flares across the electromagnetic spectrum and the availability of spacecraft in situ measurements of solar ejecta. In this paper, we review some results obtained with the Clark Lake multifrequency radioheliograph at meter-decameter wavelengths and from satellite multifrequency directive observations at hectometer and kilometer wavelengths. We present evidence that type III electrons propagate in dense coronal streamers, and that frequently observed microbursts (presumably of type III) at meter-decameter wavelengths are due to plasma radiation. We discuss observations of hectometer and kilometer type III radio storms which reveal information about active region structures, interplanetary magnetic field configuration, and solar wind acceleration. We also discuss kilometer type II bursts, interactions between type III electrons and interplanetary shocks, and present some new results on shock associated (SA) events. Title: Relative positions of microwave and hard X-ray burst sources Authors: Kundu, M. R. Bibcode: 1984AdSpR...4g.157K Altcode: 1984AdSpR...4Q.157K Simultaneous microwave and hard X-ray imaging observations of 12 bursts show that it is difficult to discern a general pattern between microwave and hard X-ray burst locations. In general, the microwave source is displaced from the hard X-ray source. The commonly believed behavior of the microwave source being located near the top and hard X-ray source near the footpoints of a loop appears to be true in some cases but not all. If the burst source is simple, both may be located near loop tops. Sometimes when the hard X-ray source has two components, one weak and one strong, the microwave source is not located over a neutral line (loop top) but close to a sunspot where the magnetic field is strongest. It appears that more than one loop or arcade may sometimes be involved in the microwave and hard X-ray emission. This is particularly true when several interacting loops trigger the onset of a flare. Title: Solar Terrestrial Physics Authors: Kundu, M. R.; Biswas, B.; Reddy, B. M.; Ramadurai, S. Bibcode: 1984stp..conf.....K Altcode: No abstract at ADS Title: Recent advances in solar radio physics. Authors: Kundu, M. R. Bibcode: 1984PIASE..93..201K Altcode: The author reviews high spatial resolution microwave observations of solar active regions, coronal loops and flares. Observations of preflare active regions are presented; in particular the author discusses the interpretations of reversal of polarization at the flare site and the role of newly emerging flux in triggering the onset of flares. He discusses the spatial locations of microwave burst emitting regions; loops or arcades of loops appear to be the sites of flare energy release in microwave bursts. Title: Millisecond time structures in hard x-ray bursts from Sun Authors: Krishan, V.; Kundu, M. R. Bibcode: 1984stp..conf..147K Altcode: No abstract at ADS Title: Radio and Visible Light Observations of a Coronal Arcade Transient Authors: Gergely, T. E.; Kundu, M. R.; Erksine, F. T., III; Sawyer, C.; Wagner, W. J.; Illing, R.; House, L. L.; McCabe, M. K.; Stewart, R. T.; Nelson, G. J.; Koomen, M. J.; Michels, D.; Howard, R.; Sheeley, N. Bibcode: 1984SoPh...90..161G Altcode: We discuss simultaneous visible-light and radio observations of a coronal transient that occurred on 9 April, 1980. Visible-light observations of the transient and the associated erupting prominence were available from the Coronagraph/Polarimeter carried aboard SMM, the P78-1 coronagraph, and from the Haleakala Observatory. Radio observations of the related type III-II-IV bursts were available from the Clark Lake and Culgoora Observatories. The transient was extremely complex; we suggest that an entire coronal arcade rather than just a single loop participated in the event. Type III burst sources observed at the beginning of the event were located along a nearby streamer, which was not disrupted, but was displaced by the outmoving loops. The type II burst showed large tangential motion, but unlike such sources usually do, it had no related herringbone structure. A moving type IV burst source can be associated with the most dense feature of the white-light transient. Title: Association Between X-Ray and Meter - Decameter Bursts (stip Interval Viii) Authors: Sawant, H. S.; Kane, S. R.; Kundu, M. R.; Gergely, T. E. Bibcode: 1984sii..conf..113S Altcode: No abstract at ADS Title: Hydrologic appraisal of rivers plan-form at confluence zone - A case study using Landsat MSS data Authors: Shevgaonkar, R. K.; Kundu, M. R. Bibcode: 1984AdSpR...4g.247S Altcode: 1984AdSpR...4..247S In river systems confluences and bifurcations are typical features whose effects are largely dependent on the specific characteristics of the rivers involved. The study makes an attempt to analyse the planform configuration at the confluence zone of the Wainganga and Khobragadi rivers in the central part of India. The data used are the Landsat MSS CCT data of date 17.12.1972 for scene 154-046 and black and white aerial photographs of November, 1969. Supervised method of classification using maximum likelihood classification method is employed. The study confirms that the discharge and sediment transport in the individual rivers constitute the dominating factors in the changes of planform geometry at a confluence. The usefulness of the Landsat MSS data and digital analysis techniques. for generating the necessary data inputs for the study is also validated. Title: High spatial resolution microwave observations of Solar Flares Authors: Kundu, M. R. Bibcode: 1984stp..conf..159K Altcode: No abstract at ADS Title: VLA observations of "compact" sources in CTB 80. Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1983JApA....4..253V Altcode: High resolution (3 arcsec-4 arcsec) maps of three compact sources in CTB 80, observed with the Very Large Array at 6 and 20 cm wavelengths are presented. The central core consists of a limb-brightened shell (of diameter 30 arcsec) superimposed on a diffuse emission of size 75 arcsec x 45 arcsec. The compact sources 1949+324 and 1952+332 located near the tips of the southwest and northeast ridges are rather remarkable and possibilities for these to be fragments ejected by the SN are examined. 1949+324 is fully resolved by the 4 arcsec beam and shows structure with multiple components oriented perpendicular to the ridge. 1950+326 is a background radio source. Title: Optical, microwave and UV imagery of a solar flare. Authors: Gaizauskas, V.; Kundu, M. R.; Schmahl, E. J.; Shine, R. A.; Woodgate, B. E. Bibcode: 1983JRASC..77..261G Altcode: No abstract at ADS Title: The Thermal Phase of Flares: A New Diagnostic Using Microwaves &GOES X-rays Authors: Schmahl, E. J.; Kundu, M. R.; Erskine, F. E. Bibcode: 1983BAAS...15..972S Altcode: No abstract at ADS Title: Three Dimensional Structures of Solar Active Regions and Flare Buildup from VLA Observations Authors: Kundu, M. R.; Shevgaonkar, R. K. Bibcode: 1983BAAS...15..972K Altcode: No abstract at ADS Title: Spatial Characteristics of Microwave Bursts Authors: Kundu, M. R. Bibcode: 1983SoPh...86..205K Altcode: The spatial characteristics of microwave bursts are discussed in relation to impulsive and post-burst phases. The existence of two components - a gradual and another spiky - in the impulsive phase is discussed from the WSRT high time and spatial resolution observations. Using the WSRT data, evidence is presented for homologous flares at 6 cm, from the similarity of their spatial structure and their temporal evolution. Preflare changes in microwave active regions are presented and their interpretations in terms of newly emerging flux at the flare site are discussed. High spatial resolution observations of the structure of microwave flaring loops and their interpretation in terms of arcades of loops as the sites of primary energy release are presented. Theoretical interpretation of the confinement of microwave producing energetic electrons in the coronal part of loops is discussed. The relative timing of the peaks of impulsive hard X-ray and microwave burst is discussed. Possible diagnostics of impulsive phase onsets from cm-λ polarization data are presented, and the role of the emergence of new flux and of the current sheet formed between closed loops in producing impulsive energy release at centimeter wavelengrths are analyzed. Title: X-Ray and Microwave Observations of Active Regions Authors: Webb, D. F.; Davis, J. M.; Kundu, M. R.; Velusamy, T. Bibcode: 1983SoPh...85..267W Altcode: We compare coordinated, high spatial resolution (2-3 arc sec) observations at 6 cm and in soft X-rays with photospheric magnetograms and optical filtergrams of two active regions. The correspondence of the brightest centimetric components in these regions with coronal loops, sunspots and pores, chromospheric structures and the photospheric magnetic field was determined. Our principal results are: The association between the microwave components and coronal X-ray and photospheric magnetic field structures is complex; in general X-ray emission was not associated with the microwave components. A majority of the components were not associated with sunspots, although the brightest (Tb ≥ 4 × 106 K) components overlay regions of strong photospheric field or high field gradients. Several of the components coincided with the apparent bases of shorter coronal loops and 4 with the tops of X-ray loops. Title: Direct evidence of type III electron streams propagating in coronal streamers Authors: Kundu, M. R.; Gergely, T. E.; Turner, P. J.; Howard, R. A. Bibcode: 1983ApJ...269L..67K Altcode: Using two-dimensional solar images at 73.8 MHz, obtained with the Clark Lake Multifrequency Radioheliograph, the authors present direct evidence that type III electron streams propagate in dense coronal streamers. This evidence is substantiated by the excellent coincidence that is found in position angle between the densest parts of streamers observed with the Solwind coronagraph on the P78-1 satellite and the maximum brightness of type III burst sources. Title: VLA observations of a solar active region and coronal loops Authors: McConnell, D.; Kundu, M. R. Bibcode: 1983ApJ...269..698M Altcode: In May 1981, observations of a solar active region at 6 cm and 20 cm were conducted with the aid of a Very Large Array (VLA). It was found that the 6 cm emission was associated with sunspots and transverse magnetic fields between spots. The 20 cm emission came from elongated sources connecting regions of opposite magnetic polarity. The sources of the emission at 20 cm could be identified as coronal loops. A model for hydrostatic loops proposed by Rosner et al. (1978) was employed to determine a likely mechanism for the emission at 20 cm. It was found that a two-component model of bremsstrahlung emission from the feet and gyroresonance emission from the top of the loops can satisfactorily explain the observations. Title: Network to Cell Contrast at Microwaves Authors: Chiuderi Drago, F.; Kundu, M. R.; Schmahl, E. J. Bibcode: 1983SoPh...85..237C Altcode: Using different models deduced from EUV lines for the cell and for various network components, the corresponding radio brightness temperature in the millimetric and centimetric range of wavelengths are computed. The contrast C = [Tb (network)]/[Tb (cell)] and the difference ΔT = Tb (network) - Tb (cell) are compared with the few available observations of the quiet Sun inhomogeneities performed with sufficient angular resolution. The comparison shows a satisfactory agreement with most of the observations. Title: A coronal transient associated with a high-speed type II burst Authors: Gergely, T. E.; Kundu, M. R.; Hildner, E. Bibcode: 1983ApJ...268..403G Altcode: Several characteristics of a white light transient observed by the ATM Coronagraph experiment aboard Skylab are discussed. The transient was associated with a very high speed type II radio burst. The observed plane of the sky speed of the burst was 4900 km/s, 6-7 times higher than the speed of the transient itself. Based on the relative speeds of the transient and the radio burst, it is argued that the type II disturbance must have propagated in a still undisturbed corona, at an approximately 35-deg angle to the preexisting streamer and along an essentially open field configuration. The electron density gradients derived from the radio and the white light observations are compared, and it is shown that they are in agreement within the limits of the observations. The assumption that the type II was a weak MHD shock leads to large values for the coronal magnetic field. The possibility that the type II radition originated in a strong shock, with a magnetic Mach number greater than 2, is considered. Title: Microwave, Soft and Hard X-ray Imaging Observations of Two Solar Flares Authors: Kundu, M. R.; Machado, M.; Erskine, F. T.; Rovira, M. G.; Schmahl, E. J. Bibcode: 1983BAAS...15..714K Altcode: No abstract at ADS Title: First Results from the Clark-Lake Multifrequency Radioheliograph Authors: Kundu, M. R.; Erickson, W. C.; Gergely, T. E.; Mahoney, M. J.; Turner, P. J. Bibcode: 1983SoPh...83..385K Altcode: We give a brief description of the Clark Lake Multifrequency Radioheliograph which is presently used for solar research in the frequency range 20-125 MHz. We present two-dimensional images of the Sun's corona at several frequencies within this range, obtained with time resolution as good as 1.28 s. The shape of the Sun's outer corona as observed at meter-decameter wavelengths appears to change in time periods as short as a few seconds. Title: Decameter Wavelength Observations of the Quiet Sun Authors: Gergely, T. E.; Gross, B. D.; Kundu, M. R. Bibcode: 1983BAAS...15Q.716G Altcode: No abstract at ADS Title: Ground based solar radio observations during solar maximum mission Authors: Kundu, M. R. Bibcode: 1983STIN...8320887K Altcode: The Very Large Array (VLA) and the Westerbork Synthesis Radio Telescope (WSRT) were used for making aperture synthesis maps of solar active and flaring regions. Observations of the Flare buildup in the form of increased intensity and polarization were made. Ring structure associated with sunspots were interpreted as due to the existence of cool material above the spot. Model computations were performed to explain the total intensity and polarization structures of a continuous set of active region maps. Title: Thermal and Nonthermal Phenomena in Solar Flare Loops at 20-CM Wavelength and in X-Rays Authors: Schmahl, E. J.; Kundu, M. R.; Landecker, P. B.; McKenzie, D. L. Bibcode: 1983SoPh...83....3S Altcode: 1983STIN...8424522S We present X-ray images from the P78-1 satellite for a long-lasting burst at 20 cm wavelength mapped with the Very Large Array on 19 May, 1979 by Velusamy and Kundu (1981). The decimeter wave observations were originally interpreted in terms of two models, one invoking thermal electrons radiating at low harmonics of the gyrofrequency, and the other invoking mildly relativistic electrons emitting gyrosynchrotron radiation. If indeed the 20 cm source is thermal, it should also be visible in soft X-rays, while if it is nonthermal, the soft X-ray emission should be weak or spatially or temporally distinct from the 20 cm burst. We find that only one of the three 20 cm sources was approximately co-spatial with the soft X-ray source, and that it was only partially thermal. The 20 cm burst is therefore primarily decimeter type IV emission from mildly relativistic electrons of the post-flare phase. The long lifetime (≳ 2h) and smooth temporal variation of the burst belie its nonthermal nature and suggest continuous acceleration as well as long term storage of energetic electrons. Title: Observations of H-alpha and microwave brightening caused by a distant solar flare Authors: Kundu, M. R.; Rust, D. M.; Bobrowsky, M. Bibcode: 1983ApJ...265.1084K Altcode: Three subflares were observed at 6 cm λ and at Hα (6563 Å) with the VLA and the Solar Observing Optical Network high resolution telescopes. Synthesized maps with integration times of 10 and 30 s show that most of the 6 cm burst emission originated in ≡10arcsec - 15arcsec features coincident with or adjacent to Hα flare kernels. During the onset of one of the subflares 6 cm emission was discovered in a loop stretching >105 km from the primary flare site; this emission was associated with faint Hα flarelike brightness at the remote footpoint of the loop. Assuming that the energy for the distant brightening originated at the primary flare site, it is found that ≡4 × 1024 ergs s-1 propagated along the connecting magnetic loop at a velocity of ≥ 6000 km s-1. Various possible mechanisms for the distant activation are discussed. Title: Magnetic development of flaring regions at centimeter wavelengths Authors: Kundu, M. R. Bibcode: 1983ASSL..102..335K Altcode: 1983ards.proc..335K; 1983IAUCo..71..335K A hard X-ray associated impulsive 6 cm burst observed by Kundu et al. (1981) on June 25, 1980, is considered along with several preflare 6 cm maps related to this event. The maps show that the region is very complex and consists of numerous components. Many of these components are bipolar. The components have brightness temperatures in the range from 6,000,000 to 9,000,000 K during the hour before the flare. Some of the observed phenomena might imply the emergence of a flux of reverse polarity at coronal levels. It is believed that the reverse polarity may be caused by the expansion of a preexisting flux tube in which twisting increases its coronal magnetic field. Title: REVIEW ARTICLE: Advances in solar radio astronomy Authors: Kundu, M. R. Bibcode: 1982RPPh...45.1435K Altcode: The status of the observations and interpretations of the sun's radio emission covering the entire radio spectrum from millimeter wavelengths to hectometer and kilometer wavelengths is reviewed. Emphasis is given to the progress made in solar radio physics as a result of recent advances in plasma and radiation theory. It is noted that the capability now exists of observing the sun with a spatial resolution of approximately a second of arc and a temporal resolution of about a millisecond at centimeter wavelengths and of obtaining fast multifrequency two-dimensional pictures of the sun at meter and decameter wavelengths. A summary is given of the properties of nonflaring active regions at millimeter, centimeter, and meter-decameter wavelengths. The properties of centimeter wave bursts are discussed in connection with the high spatial resolution observations. The observations of the preflare build-up of an active region are reviewed. High spatial resolution observations (a few seconds of arc to approximately 1 arcsec) are discussed, with particular attention given to the one- and two-dimensional maps of centimeter-wavelength burst sources. Title: Solar microwave bursts — A review Authors: Kundu, M. R.; Vlahos, L. Bibcode: 1982SSRv...32..405K Altcode: We review the observational and theoretical results on the physics of microwave bursts that occur in the solar atmosphere. We particularly emphasize the advances made in burst physics over the last few years with the great improvement in spatial and time resolution especially with instruments like the NRAO three element interferometer, Westerbork Synthesis Radio Telescope and more recently the Very Large Array (VLA). We review the observations on pre-flare build-up of an active region at centimeter wavelengths. In particular we discuss the observations that in addition to the active region undergoing brightness and polarization changes on time scales of the order of an hour before a flare, there can be a change of the sense of polarization of a component of the relevant active region situated at the same location as the flare, implying the emergence of a flux of reverse polarity at coronal levels. The intensity distribution of cm-λ bursts is similar to that of soft X-ray and hard X-ray bursts. Indeed, it appears that the flaring behavior of the Sun at cm wavelengths is similar to that of some other cosmic transients such as flare stars and X-ray bursters. We discuss three distinct phases in the evolution of cm bursts, namely, impulsive phase, post-burst phase, and gradual rise and fall. The radiation mechanism for the impulsive phase of the microwave burst is gyrosynchrotron emission from mildly relativistic electrons that are accelerated near the energy release site and spiral in the strong magnetic field in the low corona. The details of the velocity distribution function of the energetic electrons and its time evolution are not known. We review the spectral characteristics for two kinds of velocity distribution, e.g., Maxwellian and Maxwellian with a power law tail for the energetic electrons. In the post-burst phase the energetic electrons are gradually thermalized. The thermal plasma released in the energy release region as well as the expanded parts of the overheated upper chromosphere may alter the emission mechanism. Thus, in the post-burst phase, depending on the average density and temperature of the thermal plasma, the emission mechanism may change from gyrosynchrotron to collisional bremsstrahlung from a thermal plasma. The gradual rise and fall (GFR) burst represents the heating of a flare plasma to temperatures of the order of 106 K, in association with a flare or an X-ray transient following a filament disruption. We discuss the flux density spectra of centimeter bursts. The great majority of the bursts have a single spectral maximum, commonly around 6 cm-λ The U-shaped signature sometimes found in cm-dcm burst spectrum of large bursts is believed to a be a reflection of only the fact that there are two different sources of burst radiation, one for cm-λ and the other for dcm-λ, with different electron energy distributions and different magnetic fields. Observations of fine structures with temporal resolutionof 10 100 ms in the intensity profiles of cm-λ bursts are described. The existence of such fine time structures imply brightness temperatures in burst sources of order 1015 K; their interpretation in terms of gyrosynchrotron measuring or the coherent interaction of upper hybrid waves excited by percipitating electron beams in a flaring loop is discussed. High spatial resolution observations (a few seconds of arc to ∼ 1″ arc) are discussed, with special reference to the one- and two-dimensional maps of cm burst sources. The dominance of one sense of circular polarization in some weak 6 cm bursts and its interpretation in terms of energetic electrons confined in an asymmetric magnetic loop is discussed. Two-dimensional snapshot maps obtained with the VLA show that multi-peak impulsive 6 cm burst phase radiation originates from several arcades of loops and that the burst source often occupies a substantial portion of the flaring loop, and is not confined strictly to the top of the loop. This phenomenon is interpreted in terms of the trapping of energetic electrons due to anomalous doppler resonance instability and the characteristic scale length of the magnetic field variation along the loop. The VLA observations also indicate that the onset of the impulsive phase of a 6 cm burst can be associated with the appearance of a new system of loops. The presence of two loop systems with opposite polarities or a quadrupole field configuration is reminiscent of flare models in which a current sheet develops in the interface between two closed loops. We provide an extensive review of the emission and absorption processes in thermal and non-thermal velocity distributions. Unlike the thermal plasma where absorption and emission are inter-related through Kirchoff's law, the radiation emitted from a small population of non-thermal electrons can be reabsorbed from the same electrons (self-absorption) or from the background (thermal) electrons through gyro-resonance absorption, and free-free absorption. We also suggest that the non-thermal electrons can be unstable and these instabilities can be the source of very high brightness temperature, fine structure (∼ 10 ms) pulsations. Finally in the last part of this review we present several microwave burst models-the magnetic trap model, the two-component model, thermal model and the flaring loop model and give a critical discussion of the strength and weakness of these models. Title: Active region magnetic fields inferred from simultaneous VLA microwave maps, X-ray spectroheliograms, and magnetograms Authors: Schmahl, E. J.; Kundu, M. R.; Strong, K. T.; Bentley, R. D.; Smith, J. B., Jr.; Krall, K. R. Bibcode: 1982SoPh...80..233S Altcode: A series of VLA maps at 6 cm wavelength have been generated from observations of a solar active region (NOAA 2363) on 29 and 30 March, 1980. During the same period, X-ray spectroheliograms were acquired for this region in the lines of O VIII, Ne IX, Mg XI, Si XIII, S XV, and Fe XXV, with X-rayn Polychromator (XRP) aboard the Solar Maximum Mission (SMM). Intervals of relative quiescence (i.e., when X-ray flares and centimeter wave bursts were not evident) were selected for microwave mapping. The resulting VLA maps have spatial resolution of 4″ × 4″, and generally show two or more sources whose slowly evolving substructures have spatial scales of 10″-30″. These maps were co-registered with Hα photographs (courtesy of AF/AWS SOON, Holloman and Ramey AFB) to an accuracy of ± 8″. Similarly, the X-ray spectroheliograms have been co-registered with white light photographs to about the same accuracy. Magnetograms from KPNO and MSFC have also been co-aligned, and the magnetic X-ray, and microwave features compared. In general we have found that (a) the peaks of X-ray and 6 cm emission do not coincide, although (b) the sources in the two wavelength domains tend to overlap. These facts in themselves are evidence for the existence of opacity mechanisms other than thermal bremsstrahlung. In order to quantify this assertion, we have computed differential emission measures to derive densities and temperatures. Using these and calculated force-free magnetic fields from Kitt Peak magnetograms, we present an assessment of the mechanism of gyroresonance absorption at low harmonics of the electron gyrofrequency as the source of opacity responsible for the microwave features. We conclude that large-scale currents must be present in the active region loops to account for the bright 6 cm sources far from sunspots. Title: Correspondence Between 6 cm and Optical Images of a Solar Active Region Authors: McConnell, D.; Schmahl, E. J.; Kundu, M. R. Bibcode: 1982BAAS...14..921M Altcode: No abstract at ADS Title: Upflows Immediately Prior to the Impulsive Phase of Solar Flares Authors: Woodgate, B. E.; Shine, R. A.; Schmahl, E. J.; Kundu, M.; Gaizauskas, V. Bibcode: 1982BAAS...14..898W Altcode: No abstract at ADS Title: VLA Observations of Dramatic Changes in Fine Structure of Solar Active Regions Authors: Schmahl, E. J.; McConnell, D. M.; Kundu, M. R. Bibcode: 1982BAAS...14..924S Altcode: No abstract at ADS Title: VLA observations of the evolution of a solar burst source structure at 6 centimeter wavelength Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1982ApJ...258..388V Altcode: Evolutionary changes in the total intensity and polarization structure of a 6 cm radio burst source have been observed with the VLA, over time scales ranging from 10 s to several minutes. This burst was associated with a 2B/M1 flare observed on 1980 May 14. The 6 cm burst consisted of a gradual phase of 30 minutes duration and a strong impulsive phase of duration less than two minutes. Synthesized maps of total intensity and polarization were obtained with spatial resolution of 2 x 3 arcsec and with temporal resolutions of five minutes during the gradual phase and 10 s during the impulsive phase. The sequence of polarization maps suggests a complex magnetic field structure undergoing rapid changes. Most importantly, they show the development of two bipolar regions or quadrupole structure just prior to the impulsive energy release. Title: Positional Characteristics of Meter-Decameter Wavelength Bursts Associated with Hard X-Ray Bursts Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R. Bibcode: 1982SoPh...79..107K Altcode: Several type III, type II, and type IV bursts were observed on April 25 and 26, 1979 with the Clark Lake Radio Observatory's E-W and N-S swept frequency interferometers in the range 20-110 MHz. The radio bursts were associated with hard X-ray bursts in the energy range 26-154 keV, as observed by ISEE-3. The type III bursts, which were associated with impulsive hard X-rays, were observed to great heights (∼ 3.1R⊙ from disk center at 28 MHz) and their location indicates that the electron streams responsible for them were injected at the footpoints of magnetic field lines which diverge in the corona. With one exception, all the type III bursts occurred in dense coronal regions. Two gradual hard X-ray bursts were observed to occur in association with a type IV without type II, and a type IV-type II burst. For the gradual burst (observed on April 25) associated with a type IV only, it is believed that part of the energetic electrons responsible for meter-decameter type IV are trapped in a plasmoid behind a weak shock, as evidenced by the absence of a type II, while another part is located in low lying magnetic loops producing centimeter and hard X-radiation. The type II burst associated with the other gradual hard X-ray burst (observed on April 26) started approximately 9 min after the impulsive hard X-ray burst peak. This rather long delay between the type II onset and the impulsive maximum is believed to represent the time interval over which the shock becomes strong enough to produce a detectable type II higher in the corona. Title: Probing the Radio Sun Authors: Kundu, M. R. Bibcode: 1982S&T....64....6K Altcode: Radio studies of solar flares by the Very Large Array (VLA) of the National Radio Astronomy Observatory are discussed along with the results of cm and X-ray observations of flares. The synthesis of maps of regions of the sun just prior to flares and the validation of solar flare models using VLA are treated. Theories of the source of a flare's energy, and of the processes that produce one, are summarized. One unusual flare is cited as support for the flare model in which a current sheet develops at the interface between two closed loops. Title: Electron pitch angle scattering and the impulsive phase microwave and hard X-ray emission from solar flares Authors: Holman, G. D.; Kundu, M. R.; Papadopoulos, K. Bibcode: 1982ApJ...257..354H Altcode: Observations and theoretical considerations have led to a model for impulsive phase flare emission involving the heating and acceleration of thermal electrons in the coronal part of a magnetic loop. The bulk of the heated gas is confined between conduction fronts, but particles with velocities a few times greater than the thermal velocity can escape into the lower part of the loop. It is shown that, when the electron gyrofrequency exceeds the plasma frequency, the escaping electrons are unstable to the generation of electrostatic plasma waves which scatter the particles in pitch angle to a nearly isotropic distribution. It is also shown that this scattering can (1) enhance the microwave emission from the upper part of the loop, and (2) due to the Landau damping of both low and high phase velocity waves, can lead to one or two breaks in the impulsive-phase hard X-ray spectrum. Title: Positions of type II fundamental and harmonic sources in the 30 100 MHz range Authors: Sawant, H. S.; Gergely, T. E.; Kundu, M. R. Bibcode: 1982SoPh...77..249S Altcode: Observations of a type II burst with fundamental and harmonic structure were made, with the Clark Lake Radio Observatory's E-W and N-S sweep frequency interferometers operating in the range 120-20 MHz with time and frequency resolution of 1 s and 100 kHz, respectively. The type II burst was preceded by a type III-type V, and the associated flare of importance SN was located at S 20 W 73. The interferometric data show that the fundamental and harmonic were coincident in position. Further, the type III positions as a function of frequency were practically the same as those of the type II burst. The implications of these results are discussed. Title: Radio imaging of solar flares using the very large array - New insights into flare process Authors: Kundu, M. R.; Schmahl, E. J.; Velusamy, T.; Vlahos, L. Bibcode: 1982A&A...108..188K Altcode: An interpretation of VLA observations of microwave bursts is presented in an attempt to distinguish between certain models of flares. The VLA observations provide information about the pre-flare magnetic field topology and the existence of mildly relativistic electrons accelerated during flares. Examples are shown of changes in magnetic field topology in the hour before flares. In one case, new bipolar loops appear to emerge, which is an essential component of the model developed by Heyvaerts et al. (1977). In another case, a quadrupole structure, suggestive of two juxtaposed bipolar loops, appears to trigger the flare. Because of the observed diversity of magnetic field topologies in microwave bursts, it is believed that the magnetic energy must be dissipated in more than one way. The VLA observations are clearly providing means for sorting out the diverse flare models. Title: Time Variability and Structure of Quiet Sun Sources at 6-CM Wavelength Authors: Erskine, F. T.; Kundu, M. R. Bibcode: 1982SoPh...76..221E Altcode: Using the Westerbork Synthesis Radio Telescope (WSRT) we produced a synthesized map of a quiet Sun region on June 15, 1976, and studied the structure and time variability of the quiet emitting regions at 6 cm wavelength with a spatial resolution of 6 arc sec. Comparison of the 12hr synthesis map with Ca+ K filtergram shows that bright and dark features on the 6 cm quiet Sun synthesized map correspond to the chromospheric networks and cells observed in Ca+ K. All 6 cm bright features lie over bright Ca+ K network elements. The reverse correlation is not true, that is, not all bright Ca+ K network features have their 6 cm counterparts. Comparison with the photospheric magnetogram shows that about 72% of the photospheric magnetic field enhancements (¦B¦ ≥ 5 G) are coincident with 6 cm emissive regions. Only one 6 cm feature could be positively identified with a bipolar magnetic structure. This implies that no more than 20-25% of the 6 cm emitting features could be associated with X-ray bright points. Intercomparison of our 12hr two-dimensional synthesis map, a 4hr two-dimensional synthesis map (around meridian) and the one-dimensional fan beam scans of the quiet Sun region at 6 cm, along with the Ca+ K filtergram and photospheric magnetogram shows that: (1) All of the 15 time-varying elements at 6 cm were located on Ca+ K networks; (2) about 40% of the 15 time varying elements at 6 cm are coincident with enhancements of the photospheric magnetogram; (3) individual time-varying sources have minimum source size (FWHM) of ∼15 arc sec and maximum brightness temperature of ∼105 K; (4) the life time of the time varying sources varies from a few minutes to several tens of minutes; (5) the intensity of the sources varies by factors of 2 to 7 over time periods of ∼1 min to tens of minutes; and (6) the sources tend to disappear for periods of up to tens of minutes and to reappear at the same locations. Title: Observations of ring structure in a sunspot associated source at 6 centimeter wavelength Authors: Alissandrakis, C. E.; Kundu, M. R. Bibcode: 1982ApJ...253L..49A Altcode: The detection of a new kind of sunspot-associated source in which the emission comes predominantly from a ring structure with size between that of the umbra and the penumbra is reported. The absence of emission from the center of the spot is interpreted in terms of the orientation of the magnetic field and the presence of low temperature material above the umbra. Title: Magnetic structure of a flaring region producing impulsive microwave and hard X-ray bursts. Authors: Kundu, M. R.; Schmahl, E. J.; Velusamy, T. Bibcode: 1982ApJ...253..963K Altcode: Using VLA observations of the 1B/M1 flare of June 25, 1980, 6-cm 'snapshot' maps are synthesized. The spatial and temporal resolutions during the 9 minutes of the impulsive phase were, respectively, 1 arcsec x 2 arcsec and 10 s. Some displacement is noted between the locations of the burst source and the preflare loop structures seen in the preflare map. The burst peak occurred on the neutral line of the preflare polarization map, between the two oppositely polarized microwave 'loop' structures approximately 40 arcsec long. Concurrent hard X-ray observations were made of the burst, although these had no spatial resolution. The 6-cm maps show the locations of a number of the X-ray burst spikes. The 6-cm burst was fully resolved into at least eight components, many of which were bipolar. Title: Simultaneous mapping of microwave burst sources with the VLA at 2, 6 and 20 cm wavelengths. Authors: Kundu, M. R.; Velusamy, T.; McConnell, D. Bibcode: 1982BAAS...14..572K Altcode: No abstract at ADS Title: Centimeter Wavelength Observations of Active Regions and Flares with a Few Arc-Second Resolution Authors: Kundu, M. R. Bibcode: 1982coas.conf..119K Altcode: 1982cia..conf..119K No abstract at ADS Title: Physics of the impulsive phase of solar flares Authors: Kundu, M. R. Bibcode: 1982AdSpR...2k.159K Altcode: 1982AdSpR...2..159K The physics of the impulsive phase of solar flares is discussed in relation to high resolution microwave, hard X-ray and ultraviolet observations. High spatial resolution observations of the structure of microwave flaring loops and their interpretation in terms of arcades of loops as the sites of primary energy release are presented. Theoretical interpretation of the confinement of microwave producing energetic electrons in the coronal part of loops is discussed. High temporal and spatial resolution measurements in hard X-rays, as well as observations of the spectral evolution of the hard X-ray emission are presented. Observations of the relative locations of microwave and hard X-ray emitting regions are presented and their significance with respect to the energy release site and electron acceleration is discussed. The relative timing of the peaks of impulsive hard X-ray and microwave burst is discussed. The significance of ultraviolet measurements in obtaining the density of flaring regions is discussed. Possible diagnostics of impulsive phase onsets from cm-λ polarization data are presented, and the role of the emergence of new flux and of the current sheet formed between closed loops in producing impulsive energy release at centimeter wavelengths are analyzed. Decimeter and meter wave manifestations of preflash phase and millisecond pulsations at centimeter and decimeter wavelengths and the relevant physical processes involved are discussed. Title: VLA observations of positions 42 6 centimeter burst peaks associated with hard X-ray burst spikes Authors: Kundu, M. R.; Bobrowsky, M.; Velusamy, T. Bibcode: 1981ApJ...251..342K Altcode: Using the Very Large Array with a spatial resolution of 3 arcsec, two-dimensional, 10-second synthesis maps are produced of four 6-cm lambda bursts associated with multiply spiked hard X-ray bursts (20-300 keV). The positional, structural, and polarization characteristics are investigated. It is noted that three of the four burst sources are rather compact (less than approximately 10 arcsec). It is found that the positions of the individual peaks or spikes within a single burst are the same within plus or minus 2 arcsec. Interpreting these different peaks as separate electron acceleration events, the results suggest repeated acceleration of electrons within the same magnetic trap. The trap situation is found to be consistent with the bipolar nature of the burst sources except in one case. Title: New meter-wavelength observations of S 147 Authors: Angerhofer, P. E.; Kundu, M. R. Bibcode: 1981AJ.....86.1003A Altcode: High-resolution 430-MHz (69.8 cm) continuum observations of the galactic supernova remnant S 147 are presented. The presence of embedded numerous small-diameter radio sources producing a well defined radio shell, and a pronounced break in the flux density spectrum are suggested. Four 4C sources, several B2 sources and three anonymous sources are included, and the mean spectral index of these sources is found to be significantly less than that of typical extragalactic sources. Due to the distribution of the angular diameters, it is also suggested that the sources belong to the galactic sources, although the numbers do not represent an excess over that expected from background source counts. It is concluded that S 147 is in a relatively late stage of remnant evolution, and the sources may be a result of ionization of neutral material by the advancing shock. Title: Book-Review - Radio Physics of the Sun Authors: Kundu, M. R.; Gergely, T. E.; Layzer, D. Bibcode: 1981Natur.291..518K Altcode: No abstract at ADS Title: Observations of Solar Filaments at 8-GHZ 15-GHZ 22-GHZ and 43-GHZ Authors: Schmahl, E. J.; Bobrowsky, M.; Kundu, M. R. Bibcode: 1981SoPh...71..311S Altcode: On April 3, 4, 6, and 8, 1978, solar observations were made using the Haystack 120 ft telescope at 8, 15, 22, and 43 GHz. Hα filtergrams obtained at the Sacramento Peak Observatory on the same days showed an average of more than 30 filaments or filament fragments (per day) on the disk. Most of these appeared as depressions in brightness temperature at 15 and 22 GHz. Because of the relatively low spatial resolution at 8 GHz, only a few appeared at that frequency, and presumably because of lower opacity in filaments at higher frequencies, few depressions were visible at 43 GHz. At 15 and 22 GHz, more depressions appeared than Hα filaments, but virtually all the radio depressions overlay magnetic neutral lines. Taking the data sets for each day as independent samples, we found that at 22 GHz, 46 of the 77 radio depressions were associated with Hα filaments; at 15 GHz the correlation was smaller; only 27 out of 48 being associated with the Hα filaments. The data imply that the microwave depression features are the result of absorption by filaments and perhaps also the result of other effects of the associated filament channel, but not necessarily coronal depletion. The effects of filament absorption are, statistically, about twice as effective as other phenomena (such as absorption by material invisible in Hα, for example) in creating the radio depression. A center-to-limb study of a single large filament clearly showed that at 15 and 22 GHz the absorption by cool hydrogen supported above the neutral line was the predominant factor in producing the observed depression at radio frequencies. Title: Book-Review - Radio Physics of the Sun Authors: Layzer, D.; Kundu, M. R.; Gergely, T. E. Bibcode: 1981Natur.291..517L Altcode: No abstract at ADS Title: Book-Review - Radio Physics of the Sun - I.A.U. SYMP.86 Authors: Kundu, M. R.; Gergeley, T. E.; Kruger, A. Bibcode: 1981SSRv...28..223K Altcode: No abstract at ADS Title: Decameter studies of the 5 September 1973 flare Authors: Gergely, T. E.; Kundu, M. R. Bibcode: 1981SoPh...71...65G Altcode: We discuss the spectra and positions of the meter-decameter wavelength radio sources associated with the 5 September 1973 flare. We discuss the evolution of the size of the type II burst source and show that it fluctuates by a factor of 10, or larger. Consequently, the potential and kinetic energies associated with the shock are uncertain by the same factor. By comparing the positions of the type II and type III sources we conclude that while the shock wave associated with the type II was guided along high loops, the type III electrons were injected along open field lines which diverged within a short height in the corona. The characteristics of a particularly interesting type III burst with a low-frequency cut-off are discussed. We argue that nearby loops were not disrupted by the shock and that the energetic electrons produced during the event must have been injected at several sites and guided along open field lines at large distances from the flare to produce type III bursts. Title: VLA search for radio emission from stars with solar-type structures Authors: Bowers, P. F.; Kundu, M. R. Bibcode: 1981AJ.....86..569B Altcode: Results are presented of a high-sensitivity search for 6-cm radio emission from stars with evidence of active chromospheric or coronal regions. The data indicate that many of these stars have radio luminosities much less than those that have been found for known radio stars. Title: Book-Review - Radio Physics of the Sun - IAU SYMP.86 Authors: Kundu, M. R.; Gergely, T. E. Bibcode: 1981Sci...212...90K Altcode: No abstract at ADS Title: VLA Observations of Solar Flares and Tests of Flare Models Authors: Kundu, M. R. Bibcode: 1981BAAS...13..909K Altcode: No abstract at ADS Title: A Search for Microwave Counterparts of Umbral Flashes Authors: McConnell, D.; Kundu, M. R.; Schmahl, E. J.; Lites, B. Bibcode: 1981BAAS...13..858M Altcode: No abstract at ADS Title: Gyrosynchrotron Masering in Solar Flares Authors: Morrison, P. J.; Holman, G. D.; Kundu, M. R. Bibcode: 1981BAAS...13..860M Altcode: No abstract at ADS Title: Flare Buildup at 6 cm Wavelength, in UV and Hα Authors: Schmahl, E. J.; Kundu, M. R.; Woodgate, B.; Shine, R. Bibcode: 1981BAAS...13..846S Altcode: No abstract at ADS Title: Two-Dimensional Radioheliographic Pictures of the Sun's Outer Corona at 25.6-110.6 MHz Authors: Kundu, M. R.; Erickson, W. C.; Turner, P. J. Bibcode: 1981BAAS...13Q.891K Altcode: No abstract at ADS Title: Active Region Magnetic Fields Authors: Smith, J. B., Jr.; Strong, K. T.; Schmahl, E. J.; Kundu, M. R.; Krall, K. R.; Bentley, R. D. Bibcode: 1981BAAS...13..881S Altcode: No abstract at ADS Title: VLA Observations of Large Scale Microwave Brightening Following a Flare Authors: Bobrowsky, M.; Kundu, M. R.; Rust, D. Bibcode: 1981BAAS...13..846B Altcode: No abstract at ADS Title: Interpretation of Microwave and X-Ray Bursts Observed with the VLA and P78-1 Authors: Schmahl, E. J.; Kundu, M. R.; Landecker, P. B.; McKenzie, D. L. Bibcode: 1981BAAS...13..553S Altcode: No abstract at ADS Title: MICROWAVE_ Solar Limb Brightening Authors: Ahmad, I. A.; Kundu, M. R. Bibcode: 1981SoPh...69..273A Altcode: Previous models of microwave limb brightening have omitted the alignment of spicules along supergranule boundaries, have neglected the high temperature sheath around spicules, and have assumed an interspicular medium which was averaged over chromospheric network and non-network regions. We present a model which includes these factors. By constraining the model to conform to results from earlier UV and optical studies we are effectively left with two free parameters: the temperature at the core of the spicules, Tcore, and (at solar minimum), the interspicular chromospheric network density model of the lower transition zone. The absence of limb brightening at the short millimeter wavelengths implies Tcore ≲ 6000 k. Differences between the model and certain deconvolved observations near 9 mm are expected as a consequence of an extension of emission beyond the optical limb, predicted by the model, which affects the accuracy of the deconvolution technique. Unlike models which assume homogeneous spicules in a random distribution, ours does not require an abnormally high spicule area. Title: A multifrequency study of CTB 80 with the Westerbork synthesis radio telescope. Authors: Angerhofer, P. E.; Strom, R. G.; Velusamy, T.; Kundu, M. R. Bibcode: 1981A&A....94..313A Altcode: We report observations of the galactic supernova remnant CTB 80 (W56, G69.0 +2.7) with the Westerbork Synthesis Radio Telescope (WSRT) at 6, 2t, and 49 cm wavelengths. Maps of the brightness distribution and linear polarization are presented for each wavelength, along with discussion of the distributions of spectral index, magnetic field direction and rotation measure over the central source and radio ridges.

The new data suggest that the bright central source and the extended underlying emission are physically associated. The spectrum over the central source is flat (α ∼ 0.0), steepening uniformly away from the core in all directions. Linear polarization is detected at all three observed wavelengths. The morphology, high degree of polarization and flat spectral index of the core suggest that `the central source may belong to the Crab Nebula type SNR class.

Inspection of the PSS plates reveals the presence of considerable optical nebulosity at the position of the radio continuum peak, adding CTB 80 to the list of ∼30 optically visible supernova remnants. Title: Book-Review - Radio Physics of the Sun Authors: Kundu, M. R.; Gergely, T. E.; Maxwell, A. Bibcode: 1981S&T....62..149K Altcode: No abstract at ADS Title: Observing the Sun during Eclipses Authors: Kundu, M. R. Bibcode: 1981Mercu..10..108K Altcode: No abstract at ADS Title: VLA observations of solar active regions at 6 CM wavelength Authors: Kundu, M. R.; Schmahl, E. J.; Rao, A. P. Bibcode: 1981A&A....94...72K Altcode: Synthesized maps of two solar active regions obtained from observations with the Very Large Array (VLA) with 9-arcsec resolution are presented. The most intense sources in these regions are found to be associated with filamentary structures and magnetic neutral lines as shown in H-alpha and photospheric magnetograms. These sources are not located directly over sunspots in disagreement with earlier observations. EUV and X-ray observations have suggested that similar structures should be visible at cm wavelengths around but, outside of, sunspots if the magnetic field is sufficiently strong. These results are consistent with the locations of hot (greater than 1,000,000 K) plasmas in active regions expected from generalization based on optical photographs. Given the sizes of the radio sources, the volume emission measures of soft X-rays observed from OSO-8 rule out the possibility of thermal bremsstrahlung being of any significance, as far as the 6 cm emission is concerned. Therefore, gyroresonance absorption process is the most likely cause of 6 cm emission from these sources, and its likelihood is enhanced by the magnetic field geometry that is known to exist over filaments and neutral lines. Title: VLA observations of postflare loops at 20 centimeter wavelength Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1981ApJ...243L.103V Altcode: From observations with the VLA on May 19, 1979, the first spatially resolved observations of 20 cm radio emission originating from postflare loop systems are presented. The 20 cm burst was associated with an H alpha flare and a soft X-ray burst, and most of the intense radio emission occurred at the end of the H alpha flare and in the decay phase of the X-ray burst. The 20 cm 'snapshot' maps of the burst source obtained with a resolution of 12 arcsec x 24 arcsec show that the radio emission occurred in structures that are similar in size and shape to the systems of loops observed in X-rays. This postflare radio emission is considered to be similar to the H alpha and X-ray emissions originating in postflare loops. The radio observations of postflare loops have the unique advantage that they offer an important means of determining the average magnetic field strength in these loops. Interpreting the radio emission in this particular event as thermal gyroradiation or as nonthermal synchrotron radiation, the magnetic field strength is estimated to lie in the range of approximately 120-170 gauss. Title: Observations of the old supernova remnant S 147 at 11.1 and 18.2 cm wavelengths. Authors: Kundu, M. R.; Angerhofer, P. E.; Fuerst, E.; Hirth, W. Bibcode: 1980A&A....92..225K Altcode: New high resolution and high sensitivity radio observations of the old galactic supernova remnant S 147, made at wavelengths of 11.1 and 18.2 cm, are reported. The data reveal the presence of a well developed radio shell. The integrated flux density spectrum shows a distinct break at 1 GHz, attributed to enhanced volume emissivity of the swept-up interstellar material. The age of S 147 is likely to be about 100,000 yr, making it one of the oldest optically visible supernova remnants in the Galaxy. Derived physical parameters, based on the new data, are also reported. Title: Erratum - MICROWAVE_ EUV and X-Ray Observations of Active Region Loops - Evidence for Gyroresonance Absorption in the Corona Authors: Kundu, M. R.; Schmahl, E. J.; Gerassimenko, M. Bibcode: 1980A&A....91..377K Altcode: No abstract at ADS Title: Upper limits on the power in solar oscillations at 1.2 mm, 9 mm, 3.7 cm, and 11.1 CM wavelengths Authors: Kundu, M. R.; Schmahl, E. J. Bibcode: 1980A&A....90..192K Altcode: A search for solar oscillations has been made using the NRAO 36-ft telescope at 1.2 mm, the NRL 85-ft telescope at 9 mm, and the NRAO four-element interferometer at 3.7 and 11.1 cm wavelengths. After corrections for the small coherence length of the optically observed oscillations, for their known spectral bandwidth, and for the visibility function of the interferometer, upper limits have been placed on the fluctuating power at oscillation frequencies near 3 mHz. The interferometric observations at 3.7 cm and the single-dish observations at 1.2 and 9 mm imply that less than 0.3, 0.04, and 0.1%, respectively, of the bremsstrahlung photons emitted from the chromosphere show periodic fluctuations. This is 1 to 3 orders of magnitude less than the fraction (approximately 1 to 2%) reported at ultraviolet wavelengths. Simple arguments in terms of weak shock theory suggest that the observable oscillations at centimeter and millimeter wavelengths should be intrinsically weaker in the thermal bremmstrahlung radiation than the optical, but the 3.7 cm wavelength results are explained only by the absence of periodic fluctuations at the level of formation. Title: VLA Observations of Two SMM Flares at 6 cm Authors: Erskine, F. T.; Kundu, M. R.; Velusamy, T. Bibcode: 1980BAAS...12..901E Altcode: No abstract at ADS Title: VLA Observations of a Centimeter Wavelength Burst Associated With a Filament Eruption on May 14, 1980 Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1980BAAS...12..901V Altcode: No abstract at ADS Title: Radio and Visible Light Observations of a Coronal Transient Associated with a Prominence Eruption Authors: Gergely, T. E.; Kundu, M. R.; Erskine, F. T.; Sawyer, C.; Wagner, W. J.; Illing, R.; House, L. L.; McCabe, M. K.; Stewart, R. T.; Nelson, G. J. Bibcode: 1980BAAS...12..900G Altcode: No abstract at ADS Title: Correlated Soft X-Ray and Microwave Observations of Active Region Loops Authors: Webb, D. F.; Davis, J. M.; Kundu, M. R.; Velusamy, T. Bibcode: 1980BAAS...12..916W Altcode: No abstract at ADS Title: Nonthermal Flare Emission and the Nonlinear Dynamics of High Energy Electrons Authors: Holman, G. D.; Papadopoulos, K.; Kundu, M. R. Bibcode: 1980BAAS...12..901H Altcode: No abstract at ADS Title: VLA Observations of the Impulsive Phase of the June 25, 1980 Flare at 6 CM Wavelength Authors: Kundu, M. R.; Velusamy, T.; Schmahl, E. J. Bibcode: 1980BAAS...12..901K Altcode: No abstract at ADS Title: Comparison of VLA Microwave Maps of Active Regions with X-ray Spectroheliograms Authors: Schmahl, E. J.; Kundu, M. R.; Strong, K. T. Bibcode: 1980BAAS...12Q.907S Altcode: No abstract at ADS Title: Observation with the VLA of a stationary loop structure on the sun at 6 centimeter wavelength Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1980ApJ...240L..63K Altcode: A looplike structure connecting two sunspots of opposite polarity in an active region has been observed at 6 cm with a resolution of 3.5 arcsec, using the Very Large Array. This loop structure is reminiscent of the X-ray loops, as observed, for example, from Skylab. The brightness temperature in the 'loop' is one-million K and five-million K near its foot points. Most of the bright peaks in the 'loop' are well aligned with a long neutral line. Several compact, highly circularly polarized emission peaks were observed over emerging flux regions near one of the spots. Some of these sources appear to be associated with arch filament systems. The low brightness emission in the 'loop' is attributed to optically thin thermal bremsstrahlung. Title: Synthesized map of a solar filament at 6 CM with approximately 15 arc SEC resolution Authors: Rao, A. P.; Kundu, M. R. Bibcode: 1980A&A....86..373R Altcode: Radio telescope observations have been used to provide the first synthesized map of a filament at 6 cm with angular resolution of about 15 arcsec. The 'dirty' map of the north limb of the sun is shown along with the dirty map of the residual after subtracting the three component least squares model. There is very good correspondence between the radio contours and the H alpha filament; the darkest feature of the filament has a radio temperature depression of 7500 plus or minus 1500 K, and the corresponding brightness temperature of the filament is 12500 plus or minus 1500 K. It is concluded that for this particular filament the radio size is not larger than the optical one. Title: Time Variability and Structure of Quiet Sun Sources at 6 cm Wavelength Authors: Erskine, F. T.; Kundu, M. R. Bibcode: 1980BAAS...12..504E Altcode: No abstract at ADS Title: Observations of Solar Filaments at 8, 15, 22, and 43 Ghz Authors: Schmahl, E. J.; Bobrowsky, M.; Kundu, M. R. Bibcode: 1980BAAS...12..507S Altcode: No abstract at ADS Title: Nature of Meter-Decameter Bursts Associated with Hard X-ray Bursts Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R. Bibcode: 1980BAAS...12..478K Altcode: No abstract at ADS Title: Two-Dimensional Snapshot Maps with the VLA of a Solar Burst at 20 cm Wavelength Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1980BAAS...12..478V Altcode: No abstract at ADS Title: Observation with the VLA of a Stationary Loop Structure on the Sun at 6 cm Wavelength Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1980BAAS...12..519K Altcode: No abstract at ADS Title: Thermal Radio Emission from Solar Active Regions Authors: Holman, G. D.; Kundu, M. R. Bibcode: 1980BAAS...12..517H Altcode: No abstract at ADS Title: 6 CM observations of a solar active region and bursts with approximately 6 arcsec resolution Authors: Erskine, F. T.; Kundu, M. R.; Rao, A. P. Bibcode: 1980A&A....83..256E Altcode: The paper examines the solar active region located near N04E49, that was mapped at a 6 cm wavelength over a period of 12 hours, employing the Westerbork synthesis radio telescope. Two impulsive radio bursts were recorded during this time, one of which was associated with a chromospheric flare. One-dimensional fan beam scans of the burst sources were synthesized in order to display their time history with regard to intensity, polarization, position and size. Title: Association of flaring X-ray bright points with type III bursts Authors: Kundu, M. R.; Gergely, T. E.; Golub, L. Bibcode: 1980ApJ...236L..87K Altcode: Using the swept-frequency radio observations obtained at the Clark Lake Radio Observatory and the X-ray photographs taken by the S-054 experiment aboard Skylab, a search has been made for type III bursts associated with X-ray bright point (XBP) flares. Using temporal as well as spatial criteria for the association, four such events are found over a period of 43 days. The time period was selected in such a way that the level of flare and radio activity was low in order to minimize the chance coincidences. The detection of type III bursts from the flaring XBPs is of great interest, since it identifies them with the flare process, of which XBP flares are thought to be the simplest form. Title: A model for sunspot associated emission at 6 CM wavelength Authors: Alissandrakis, C. E.; Kundu, M. R.; Lantos, P. Bibcode: 1980A&A....82...30A Altcode: Two-dimensional maps of total intensity and circular polarization of a sunspot region at 6 cm have been calculated using a simple model for the chromosphere-corona transition region and observations of the longitudinal component of the photospheric magnetic field. The calculations are in good agreement with the high resolution observations of the same sunspot region at 6 cm, obtained with the Westerbork Synthesis Radio Telescope. It is shown that the 6 cm radiation is predominantly due to gyroresonance absorption process at the second and third harmonics of the gyrofrequency (H = 900-600 G). Estimates of the conductive flux and the electron density in the transition region above the sunspot are also given. Title: Microwave, EUV, and X-ray observations of active region loops - Evidence for gyroresonance absorption in the corona Authors: Kundu, M. R.; Schmahl, E. J.; Gerassimenko, M. Bibcode: 1980A&A....82..265K Altcode: The combined data from 3.7 and 11 cm radio maps, EUV spectroheliograms, and X-ray photographs of an active region (McMath 12379) are analyzed. The near equality of the radio brightness temperatures and the electron temperature determined from the EUV and X-ray data implies that the radio emission is thermal. Since the free-free absorption is inadequate to account for this, the large optical depth must be produced by gyroresonance absorption. It is inferred that the magnetic scale height must be of the same order as the observed width of the coronal loops (one-billion cm). The scale of emission in the radio, and hence the scale of the absorbing region transverse to the line of sight, is also of this order. Title: Solar burst observations at centimeter wavelengths Authors: Kundu, M. R. Bibcode: 1980IAUS...86..157K Altcode: Selected features of centimeter-wave solar radio burst are discussed in relation to the generating mechanism of these bursts. Observations are presented of active regions prior to the onset of a flare, the intensity distributions of flares, the impulsive phase of a burst, the post-burst phase, and gradual rise and fall burst. Analysis of high-resolution impulsive bursts leads to a model of burst emission in which impulsively accelerated plasma contained within loop structures is responsible for the impulsive burst phase by the ejection of high energy particles and for the post-burst phase by the spread of slower particles, with emission in the centimeter wave region primarily by bremsstrahlung. It is also pointed out that the impulsive centimeter-wave bursts have been found to correspond with hard X-ray bursts as well as soft X-ray kernels, indicating that the centimeter wave region is no larger than the X-ray emitting region, which would require either self-absorption or an asymmetrical bipolar field structure to explain the greater X-ray intensities. Title: Maryland, University of Authors: Kundu, M. R. Bibcode: 1980BAAS...12..226K Altcode: No abstract at ADS Title: Observations of solar active regions at 2 and 6 CM wavelengths with 3 arc second resolution Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1980IAUS...86..105V Altcode: No abstract at ADS Title: Observations of the quiet sun with 6 arcsec resolution Authors: Kundu, M. R.; Rao, A. P.; Erskine, F. T.; Bregman, J. D. Bibcode: 1980IAUS...86...53K Altcode: High-resolution observations of the quiet sun at 6 cm are reported. The Westerbork Synthesis Radio Telescope was used to observe a central 10 x 10 arcmin disk region for 12 hours at a resolution of 6 arcsec in the E-W direction and 15 arcsec in the N-S direction. The resulting radio map reveals the presence of a supergranulation network with network elements of 25,000 K and cells of 15,000 K, and which is of the same scale as the Ca(+) network. Sequential observations of the north, south, east and west limbs reveal a limb brightening of 40-60% above the mean disk temperature, the peak of which is located 15 arcsec outside the optical disk. Title: Impulsive phase of solar flares Authors: Kane, S. R.; Crannell, C. J.; Datlowe, D.; Feldman, U.; Gabriel, A.; Hudson, H. S.; Kundu, M. R.; Maetzler, C.; Neidig, D.; Petrosian, V. Bibcode: 1980sfsl.work..187K Altcode: 1980sofl.symp..187K The present understanding of the impulsive phase of a solar flare, characterized by short-duration bursts of impulsive hard X-ray, EUV, optical and radio emission indicating the release of energetic electrons is reviewed. Observations of the spectral distribution of impulsive hard X-ray bursts and of Type III and radio continuum bursts are presented and interpreted in terms of energetic electron distributions, and impulsive EUV, XUV, soft X-ray and optical observations, which provide a lower limit to total energy release during the impulsive phase, are discussed. The role of energetic electrons in exciting the hard X-ray, EUV and microwave emissions is considered, and thin-target, thick-target, partial-precipitation and thermal models of impulsive phase electron acceleration are evaluated in light of the observations. It is noted that available data do not allow discrimination between a thermal or a nonthermal electron distribution, on which depends the proportion of flare energy supplied by the energetic electrons, and that data favors models which permit at least partial electron precipitation. Future observational and theoretical work is indicated. Title: Decametric radio bursts associated with coronal loop structures Authors: Gergely, T. E.; Kundu, M. R.; Golub, L.; Webb, D. Bibcode: 1980IAUS...86..435G Altcode: The association of X-ray loop structures with type III bursts is examined using soft X-ray (2-54 A) pictures which were obtained from the Skylab S-054 experiment. The properties of meter-decameter wavelength radio bursts (type III) appear to be associated with two different kinds of loop structures: (1) short lived small scale loops, which are found to link magnetic fields of opposite polarity, called X-ray bright points (XBP); and (2) long lasting loop systems which connect opposite magnetic polarities of an active region as well as active region complexes. It is judged that the presence of active region loop complexes on the disk is a necessary yet insufficient condition for the occurrence of a decametric storm and that conditions concerning the geometry of the magnetic field must also be important in the process. Title: Radio physics of the sun: proceedings from IAU symposium no. 86, held in College Park, Md. U.S.A., August 7-10, 1979. Authors: Kundu, M. R.; Gergely, T. E. Bibcode: 1980IAUS...86.....K Altcode: Papers are presented in the areas of the radio characteristics of the quiet sun and active regions, the centimeter, meter and decameter wavelength characteristics of solar bursts, space observations of low-frequency bursts, theoretical interpretations of solar active regions and bursts, joint radio, visual and X-ray observations of active regions and bursts, and the similarities of stellar radio characteristics to solar radio phenomena. Specific topics include the centimeter and millimeter wave characteristics of the quiet sun, radio fluctuations arising upon the transit of shock waves through the transition region, microwave, EUV and X-ray observations of active region loops and filaments, interferometric observations of 35-GHz radio bursts, emission mechanisms for radio bursts, the spatial structure of microwave bursts, observations of type III bursts, the statistics of type I bursts, and the numerical simulation of type III bursts. Attention is also given to the theory of type IV decimeter bursts, Voyager observations of type II and III bursts at kilometric wavelengths, radio and whitelight observations of coronal transients, and the possibility of obtaining radio observations of current sheets on the sun. Title: An interpretation of solar flare microwave spikes as gyrosynchrotron masering Authors: Holman, G. D.; Eichler, D.; Kundu, M. R. Bibcode: 1980IAUS...86..457H Altcode: No abstract at ADS Title: Book-Review - Radio Physics of the Sun IAU Symp 86 Authors: Kundu, M. R.; Gergely, T. E. Bibcode: 1980Natur.287..373K Altcode: No abstract at ADS Title: Decameter radio and white light observations of the 21 August 1973 coronal transient Authors: Gergely, T. E.; Kundu, M. R. Bibcode: 1980IAUS...91..245G Altcode: The forces driving the ejecta of the coronal transient of August 21, 1973 are estimated using physical parameters derived by joint radio and white light observations. The radio emission associated with the transient was continuum in nature, and lasted for almost 5 hours. Simultaneous radio and white light measurements show that the radio source was cospatial with one of the secondary white light loops. Assuming a coronal temperature of 1,500,000 K, the results yield an approximate equality of the gas and magnetic pressures at 2.0 solar radii. It is concluded that for this transient, the gas is strongly influenced by changes in the magnetic field. Title: High-resolution observations of the quiet sun at 6 centimeters using the Westerbork Synthesis Radio Telescope Authors: Kundu, M. R.; Rao, A. P.; Erskine, F. T.; Bregman, J. D. Bibcode: 1979ApJ...234.1122K Altcode: High-spatial-resolution (∼6") observations of the quiet Sun were made at 6 cm with the Westerbork Synthesis Radio Telescope. A 10' × 10' field of the central disk region observed on 1976 June 16 was synthesized. We show the first radio map of the supergranulation network. Numerical autocorrelation of the radio map indicated a radio "network" width ∼11,000 km and a radio "cell" spacing ∼32,000 km. The brightness temperature of typical network elements is ∼2.5 × l04 K, while that of the radio cells is ∼1.5 × l04 K. The contrast between the radio network and cells is ∼1.7:1 which is intermediate to that of the Ca+ K network and Lα network. The radio map was compared with a Ca+ K spectroheliogram of the same region on the same day. On 1976 June 17, the four limbs of the Sun were also observed in an attempt to synthesize the limb and study the extent and symmetry of limb brightening. The results show that limb brightening is seen both in the north-south and east-west directions, contrary to earlier low-resolution measurements which showed limb brightening only in the east-west direction. The peak of the limb brightening appears ∼15" outside the white-light disk and the peak limb temperature is ∼40% greater than the mean disk temperature. Title: Upper Limits on Solar Oscillation Power in Microwaves Authors: Kundu, M. R.; Schmahl, E. J. Bibcode: 1979BAAS...11..641K Altcode: No abstract at ADS Title: Centimeter Wavelength Observations of Solar Active Regions With The Very Large Array Authors: Kundu, M. R.; Schmahl, E. J.; Rao, A. P. Bibcode: 1979BAAS...11R.710K Altcode: No abstract at ADS Title: Radio Interferometric Observations of Solar Bursts at 3.7-CM and 11.1-CM Wavelengths Authors: Kundu, M. R.; Angerhofer, P. E. Bibcode: 1979SoPh...64..159K Altcode: Several solar active regions were observed during the 1976 vernal equinox with the 3-element interferometer of the National Radio Astronomy Observatory. The element spacings for these observations were 600, 2100, and 2700 m, resulting in maximum angular resolutions of about 3 arc sec at 3.7 cm and 8.5 arc sec at 11.1 cm. We fitted the fringe visibility for each baseline pair as a function of projected baseline with a single gaussian component, and calculated the extrapolated flux at zero baseline, F0, the FWHM source size, a, and the peak brightness temperature Tb. We present physical parameters derived for the observed bursts. Title: An interpretation of the polarization structure of microwave bursts. Authors: Kundu, M. R.; Vlahos, L. Bibcode: 1979ApJ...232..595K Altcode: High-spatial-resolution (a few seconds of arc) observations of microwave bursts have demonstrated that only the impulsive phase of the burst is polarized; one observes only one polarity in the burst source if it is weak (Alissandrakis and Kundu) and both polarities if it is intense (Enome et al.). These results are interpreted in terms of an asymmetrical bipolar field structure of the loop in which the energetic electrons responsible for the radiation are contained. The role of unequal field strengths at the feet of the loop on the number of electrons trapped and their pitch angle distribution are discussed in a specific model. Computations of the polarized intensity originating from each foot of the loop seem to be consistent with the observations at present available. Title: Observations of alpha Orionis, R Aquilae, and R Aquarii at 14.9 GHz. Authors: Bowers, P. F.; Kundu, M. R. Bibcode: 1979AJ.....84..791B Altcode: The 14.9-GHz continuum flux densities of the M-type stars Alpha Ori, R Aql, and R Aqr have been measured. For Alpha Ori and R Aql it is suggested that the emission at this frequency is primarily due to ionized gas associated with stellar chromospheres or coronae. For R Aqr a model consistent with available data is proposed in which the variable intensity of the radio emission depends on a variable mass-loss rate for the Mira. Title: Radio and white-light observations of the 1973 August 21 coronal transient. Authors: Gergely, T. E.; Kundu, M. R.; Munro, R. H.; Poland, A. I. Bibcode: 1979ApJ...230..575G Altcode: A coronal transient, which occurred on August 21, 1973, has been observed simultaneously in white light and at decameter radio wavelengths. The radio observations were obtained with a two-dimensional swept-frequency array (called the Teepee Tee). The white-light observations consist of a series of photographs taken by the High Altitude Observatory's coronagraph aboard Skylab. The radio emission associated with the transient was continuum in nature and lasted for almost 5 hours. The source of emission was observed to be cospatial with the lower part of one of the secondary white-light loops. A lower limit of 0.6 solar radius for the depth (extension along the line of sight) of this part of the transient was derived from considerations of radio-wave propagation in the corona. The radio source showed no dispersion of height with frequency, and, therefore, the emission is attributed to gyrosynchrotron radiation. Based on this assumption, the magnetic-field strength in the lower part of the loop is estimated to be in the 2.0-4.5-gauss range at a height of 2.1 solar radii from the center of the sun. Title: Solar Atmospheric Inhomogeneities and Limb Brightening Models Authors: Ahmad, I. A.; Kundu, M. R. Bibcode: 1979BAAS...11..410A Altcode: No abstract at ADS Title: Radiobeobachtungen an S 147, ein Beitrag zur Diskussion alter Supernovaüberreste Authors: Fürst, E.; Hirth, W.; Angerhofer, P. E.; Kundu, M. R.; Sofue, Y. Bibcode: 1979MitAG..45..103F Altcode: No abstract at ADS Title: Comparison of radio and EUV filaments: a two-component model. Authors: Kundu, M. R.; Schmahl, E. J. Bibcode: 1979BAAS...11..393K Altcode: No abstract at ADS Title: Discussion Authors: Landi Degl'Innocenti, M.; Kundu, M. R.; Landman, D. A.; Smartt, R. N.; Stenflo, J. Bibcode: 1979phsp.coll...85L Altcode: 1979IAUCo..44...85D; 1979phsp.coll...85D No abstract at ADS Title: Discussion Authors: Acton, L. W.; Engvold, O.; Heasley, J. N.; Heyvaerts, J.; Hirayama, T.; Kundu, M. R.; Leroy, J. L.; Malville, J.; Rust, D. M.; Zirin, H. Bibcode: 1979phsp.coll...31A Altcode: 1979IAUCo..44...31A No abstract at ADS Title: Discussion Authors: Kundu, M. R.; Schmahl, E. J. Bibcode: 1979phsp.coll..129K Altcode: 1979IAUCo..44..129K No abstract at ADS Title: A broad look at solar physics adapted from the solar physics study of August 1975 Authors: Parker, E.; Timothy, A.; Beckers, J.; Hundhausen, A.; Kundu, M. R.; Leith, C. E.; Lin, R.; Linsky, J.; MacDonald, F. B.; Noyes, R. Bibcode: 1979sswp.book....3P Altcode: 1979sswp.book....3B The current status of our knowledge of the basic mechanisms involved in fundamental solar phenomena is reviewed. These include mechanisms responsible for heating the corona, the generation of the solar wind, the particle acceleration in flares, and the dissipation of magnetic energy in field reversal regions, known as current sheets. The discussion covers solar flares and high-energy phenomena, solar active regions; solar interior, convection, and activity; the structure and energetics of the quiet solar atmosphere; the structure of the corona; the solar composition; and solar terrestrial interactions. It also covers a program of solar research, including the special observational requirements for spectral and angular resolution, sensitivity, time resolution, and duration of the techniques employed. Title: Discussion Authors: Chiuderi-Drago, F.; Kundu, M. R.; Lantos, P.; Zirin, H. Bibcode: 1979phsp.coll..134C Altcode: 1979IAUCo..44..134C No abstract at ADS Title: Observations of Filaments at Centimeter and Millimeter Wavelengths. Authors: Kundu, M. R. Bibcode: 1979phsp.coll..122K Altcode: 1979IAUCo..44..122K; 1979phsp.conf..122K Observations of quiescent-prominence radio filaments at centimeter and millimeter wavelengths are reviewed. The finding that a radio filament appears cooler than the background quiet sun is interpreted by postulating that the filament is cool and optically thick, in which case the brightness temperature of the filament should be the same as its kinetic temperature. Optical spectroscopic observations are discussed which indicate that a typical filament has an electron density of approximately 100 billion per cu cm, a temperature of about 6000 K, and a length of approximately 1000 km, implying that the optical thickness is much greater than unity for all frequencies less than 600 GHz. Millimeter- and centimeter-wavelength observations of filaments at the limb are shown also to support the view that the filaments are optically thick at these wavelengths. Radio observations of filament transition sheaths and cavities are also examined. Title: Discussion Authors: Acton, L. W.; Kundu, M. R.; Maltby, P.; Malville, J.; Orrall, F. Q.; Sheeley, N.; Spicer, D. S. Bibcode: 1979phsp.coll..225A Altcode: 1979IAUCo..44..225A No abstract at ADS Title: Discussion Authors: Anzer, U.; Chiuderi-Drago, F.; Kundu, M. R.; Leroy, J. L.; Malville, J.; Rompolt, B.; Sheeley, N.; Stenflo, J.; Tandberg-Hanssen, E.; Öhman, Y. Bibcode: 1979phsp.coll...77A Altcode: 1979IAUCo..44...77A No abstract at ADS Title: Fine structure and time variation of the quiet sun at 1.3 cm. Authors: Rao, A. P.; Kundu, M. R. Bibcode: 1978SoPh...59..345R Altcode: The Hat Creek two-element interferometer has been used to study the quiet Sun at 22 GHz. A statistical analysis of output of the interferometer clearly shows the existence of time variations on the quiet Sun with time scales ∼180 s. The observations suggest that the fine structure on the quiet Sun might consist of two components - one which varies with the time scales ∼3 min and the other being relatively stable. The average visibility amplitude indicates that the fine structure on the Sun has a typical angular size of ∼6″. The observation that the variance and the mean of the visibility amplitudes depend in the same way on the projected baseline suggests that the transient sources have angular size similar to the average size of the fine structure on the quiet Sun. Power spectra of the output of the interferometer show no significant periodicity. Title: High Resolution Observations of the Quiet Sun at 6 cm Using the Westerbork Synthesis Radio Telescope Authors: Kundu, M. R.; Rao, A. P.; Erskine, F. T.; Bregman, J. D. Bibcode: 1978BAAS...10Q.686K Altcode: No abstract at ADS Title: Decameter Radio Observations of the 5 September, 1973 Flare Authors: Gergely, T. E.; Kundu, M. R. Bibcode: 1978BAAS...10R.672G Altcode: No abstract at ADS Title: High resolution observations of CTB 80 at 6.21 and 50 centimetres. Authors: Velusamy, T.; Angerhofer, P.; Kundu, M. R.; Storm, R. Bibcode: 1978BASI....6...53V Altcode: No abstract at ADS Title: 6 centimeter observations of solar bursts with 6" resolution. Authors: Alissandrakis, C. E.; Kundu, M. R. Bibcode: 1978ApJ...222..342A Altcode: During May 1974 data were collected on nine 6-cm solar bursts originating in two active regions. One-dimensional fan-beam scans were obtained every 30 seconds in order to study burst structure and evolution. Maximum burst flux was in the 0.34-12.0 sfu range. At maximum intensity the estimated brightness temperatures were in the 10 to the 6th to 2 x 10 to the 7th K range. Angular sizes ranged from 7-23 arcsec. In most cases an expansion of the burst core after maximum intensity was observed along with a drift in the position of the burst core. Four bursts were associated important H-alpha flares, and in all cases burst maximum occurred before flare maximum. The bursts were circularly polarized in the extraordinary mode sense during maximum intensity. Since the polarization was the same over the extent of the burst source, it is suggested that if the burst is associated with loop sources, the emission is associated with one leg of the loop. Title: The association of nonthermal electrons with nonflaring coronal transients. Authors: Webb, D. F.; Kundu, M. R. Bibcode: 1978SoPh...57..155W Altcode: A close temporal and spatial association has been found between erupting filaments/coronal transients and radio noise storm continua. The three transients studied occurred away from active regions and are members of a class not usually accompanied by chromospheric emission. The data analyzed were from the S-054 soft X-ray telescope on Skylab and from one- and two-dimensional interferometers at meter and decameter wavelengths at Nançay and Clark Lake observatories. Calculations confirmed that observed microwave radiation from the transients is due to thermal bremsstrahlung. The results are consistent with an interpretation of heating of an increased amount of coronal plasma by nonthermal, 10-100 keV electrons. Three possibilities for the source of the material are described: (1) The filament material; (2) evaporation from the chromosphere or transition region; and (3) via a long-lived reconnection process. Title: Radio and White Light Observations of the 21 August 1973 Coronal Transient. Authors: Gergely, T. E.; Kundu, M. R. Bibcode: 1978BAAS...10..456G Altcode: No abstract at ADS Title: Fine Structure and Time Variation of the Quiet Sun at 1.3 cm. Authors: Rao, A. P.; Kundu, M. R. Bibcode: 1978BAAS...10..431R Altcode: No abstract at ADS Title: Radio Interferometric Observations of the Bright Core of CTB 80. Authors: Angerhofer, P. E.; Kundu, M. R. Bibcode: 1978BAAS...10..427A Altcode: No abstract at ADS Title: Possible Explanation for the turnovers in Two Solar Microwave Burst Spectra. Authors: Ahmad, I. W.; Kundu, M. R. Bibcode: 1978BAAS...10..455A Altcode: No abstract at ADS Title: Multifrequency observations of solar filaments at centimeter wavelengths. Authors: Kundu, M. R.; Fuerst, E.; Hirth, W.; Butz, M. Bibcode: 1978A&A....62..431K Altcode: Summary. On June t5 and t6, t976 we observed solar filaments at five wavelenths in the centimeter range. At t.2, 2.8, 6 and t t cm the tOO-m-dish of the Max-PlanckInstitut fur Radioastronomie was used for almost simultaneous measurements. In addition, the t3.7-m-telescope of the University of Helsinki was used at a wavelength of 0.4cm. We found a filament with a much larger size at radio than at optical wavelengths. While the diameter of the radio filament turned out to be about 2'., the one of the Ha-filament was only 0'S. This large difference is explained in terms of a filament-cavity model and the observations were used to determine the ratio of the electron densities in the cavity and in the quiet region. We found a ratio of about 3:4. Key words: solar filaments and cavities Title: A study of filament transition sheath from radio observations. Authors: Rao, A. P.; Kundu, M. R. Bibcode: 1977SoPh...55..161R Altcode: We have observed an Hα dark filament at 8, 15, and 22 GHz and derived the radio spectrum of the filament. We suggest that the filament has to be optically thick at radio frequencies and that the observed spectrum is due to the presence of a transition sheath surrounding the filament. We examine a model for the transition sheath in which the energy radiated away is balanced by the conduction of heat from the corona, and show that the radio observations indicate that little or no thermal energy is conducted into the main body of the filament. We compare the model with ultraviolet observations of filaments and discuss how the discrepancies can be removed. Title: 2.8 and 6 cm wavelength observations of NGC 7822. Authors: Angerhofer, P. E.; Kundu, M. R.; Becker, R. H.; Velusamy, T. Bibcode: 1977A&A....61..285A Altcode: Summary. We present observations of the galactic radio source W 1 (= NGC 7822) at wavelengths of 2.8 and 6 Cm. No linear polarization has been detected over this region. We conclude that the known exciting stars can account for the observed radio flux density at 6 Cm, and that W 1 is a thermal radio source. Key words: Supernova remnants - flux densities NGC7822 W1 Title: Determination of the decameter wavelength spectrum of the quiet Sun. Authors: Erickson, W. C.; Gergely, T. E.; Kundu, M. R.; Mahoney, M. J. Bibcode: 1977SoPh...54...57E Altcode: The Teepee Tee array of the Clark Lake Radio Observatory has been used to compare the flux of the Sun with that of the sidereal sources Tau A and Vir A at several frequencies in the range 109.0-19.0 MHz. Only the two central banks of the E-W arm of the array were used as elements of a phase switched interferometer so that the Sun could be observed as a point source and compared directly to the sidereal sources. The Sun was still partially resolved however, and appropriate corrections for this effect were made. The observations were taken at times when the Sun and either Tau A or Vir A were at the same declination. We have therefore been able to derive the values for the solar flux, without having to resort to a gain vs zenith distance correction. The observations, combined with those available in the literature, allow us to derive an accurate meter and decameter wavelength spectrum of the quiet Sun. Title: Coordinated X-ray, optical, and radio observations of YZ Canis Minoris. Authors: Karpen, J. T.; Crannell, C. J.; Hobbs, R. W.; Maran, S. P.; Moffett, T. J.; Bardas, D.; Clark, G. W.; Hearn, D. R.; Li, F. K.; Markert, T. H.; McClintock, J. E.; Primini, F. A.; Richardson, J. A.; Cristaldi, S.; Rodono, M.; Galasso, D. A.; Magun, A.; Nelson, G. J.; Slee, O. B.; Chugajnov, P. F.; Chugainov, P. F.; Efimov, Yu. S.; Shakhovskoj, N. M.; Shakhovskoy, N. M.; Viner, M. R.; Venugopal, V. R.; Spangler, S. R.; Kundu, M. R.; Evans, D. S. Bibcode: 1977ApJ...216..479K Altcode: We report coordinated X-ray, optical, and radio observations of the flare star YZ CMi, including the first occasion on which such a star has been monitored in all three spectral regions simultaneously. Thirty-one minor optical flares and 11 radio events were recorded. No major optical flares greater than 3 magnitudes were observed during the program. Although no flare- related X-ray emission was observed, the measured upper limits in this band enable meaningful comparisons with published flare-star models. Three of the five models predicting the relative X-ray to optical or radio flare luminosities are in serious disagreement with the observations. For the largest optical flare with coincident X-ray co1verage, the 3 a upper limit on X-ray emission in the 0.15-0.8 keV band is about 9 x 1028 ergs 5 - , corresponding to a ratio of X-ray to B-band luminosity of <0.3. Based on the present results, the fraction of the galactic component of the diffuse soft X-ray background contributed by UV Ceti-type flare stars is <9 x H, where H is the mean density of interstellar hydrogen within a few hundred parsecs of the Sun. Subject headings: radio sources: variable - stars: flare - stars: individual - X-rays: bursts Title: Observations of the quiet Sun at meter and decameter wavelengths. Authors: Kundu, M. R.; Gergely, T. E.; Erickson, W. C. Bibcode: 1977SoPh...53..489K Altcode: The new TeePee Tee array of the Clark Lake Radio Observatory has been used to observe the quiet Sun at 121.5, 73.8 and 26.3 MHz. The equatorial brightness distributions at all three frequencies, and the polar brightness distributions at the two higher ones have been measured. From the observed total fluxes and half-power diameters we have derived the peak brightness temperatures of the solar disk as well as of some sources of the slowly varying component. Title: 3.5mm Depression features associated with Hα `disparitions brusques' Authors: Kundu, M. R.; Lantos, P. Bibcode: 1977SoPh...52..393K Altcode: The characteristics of 3.5 mm depression features associated with two `disparition brusques' observed in Hα are discussed. The millimeter depressions still exist, although reduced in strength, after the disappearance of the Hα filament. The two depressions correspond to temperatures of 600 and 450 K before and to 200 and 250 K after the Hα filament disappearance. Title: 6 centimeter observations of solar active regions with 6" resolution. Authors: Kundu, M. R.; Alissandrakis, C. E.; Bregman, J. D.; Hin, A. C. Bibcode: 1977ApJ...213..278K Altcode: We have used the Westerbork Synthesis Radio Telescope for observations of solar active regions at 6 cm during 1974 May 8-10. The particular problems of using a sidereal instrument for solar observations are discussed. Maps of total intensity and circular polarization were obtained for four active regions with sunspots and a plage region; the linear polarization was below the noise limit. The brightest components of the 6 cm emission are associated with sunspots, while weaker components are associated with the plage magnetic fields, both longitudinal and transverse. An inversion of the sense of circular polarization was observed in the preceding part of a region with bipolar magnetic-field structure, about two days after the region passed through the central meridian. Nine bursts were also observed, and their one-dimensional positions with respect to the associated active regions are given. Title: Brightness distributions of the Sun at 33 and 37 GHz. Authors: Kundu, M. R.; Liu, S. -Y.; McCullough, T. P. Bibcode: 1977SoPh...51..321K Altcode: The brightness distributions of the Sun were observed at 33 and 37 GHz. Maximum limb brightening of about 10% was observed at both frequencies. Title: Polarization Properties of Solar Bursts at 6 cm Wavelength. Authors: Kundu, M. R.; Allisandrakis, C. E. Bibcode: 1977BAAS....9R.328K Altcode: No abstract at ADS Title: Determination of the Decameter Wavelength Spectrum of the Quiet Sun. Authors: Erickson, W. C.; Gergely, T. E.; Kundu, M. R.; Mahoney, M. J. Bibcode: 1977BAAS....9..371E Altcode: No abstract at ADS Title: Decameter Observations of the White Light Coronal Transient of October 27, 1973 Authors: Gergely, T. E.; Kundu, M. R.; Erickson, W. C. Bibcode: 1977BAAS....9Q.369G Altcode: No abstract at ADS Title: A Study of Filament Transition Sheath from Radio Observations. Authors: Rao, A. P.; Kundu, M. R. Bibcode: 1977BAAS....9..314R Altcode: No abstract at ADS Title: 5 GHz observations of galactic supernova remnants. Authors: Angerhofer, P. E.; Becker, R. H.; Kundu, M. R. Bibcode: 1977A&A....55...11A Altcode: Brightness and polarization distributions over several galactic supernova remnants have been observed at a wavelength of 6 cm. These observations have confirmed the nonthermal nature of most of the observed sources. It is suggested, however, that the objects G33.1-0.1 (KES 78), G35.6-0.0, G37.6-0.1, G37.7+0.1, and G37.9-0.4 are thermal. The results of these observations are presented in the form of total intensity contour maps with superimposed polarization vectors. Title: A comparison of positions and sizes of sources of centimeter and X-ray bursts. Authors: Kundu, M. R.; Alissandrakis, C. E.; Kahler, S. W. Bibcode: 1976SoPh...50..429K Altcode: We have made a parallel study of three cm-λ radio bursts, observed on 9 August, 1973 with the NRAO 1 three-element interferometer at 3.7 and 11.1 cm and the associated X-ray flares observed with the S-054 telescope aboard Skylab. Within the errors of our measurements (± 5″) the radio and X-ray events are cospatial. We find good agreement between the size of the X-ray kernel and that of the core of the cm burst, while there is evidence that much of the impulsive radio flux was produced in a larger area. Title: Observations of Solar Bursts at 6 cm Wavelength with Angular Resolution of 6" arc. Authors: Alissandrakis, C. E.; Kundu, M. R. Bibcode: 1976BAAS....8Q.555A Altcode: No abstract at ADS Title: Observations of Jupiter's Radio Emission at 327 MHz and 1410 MHz During the Pioneer 11 Fly Authors: Kundu, M. R.; Sarma, N. V. G.; Gerard, E. Bibcode: 1976BAAS....8..504K Altcode: No abstract at ADS Title: Observation of a coronal hole at 85 GHz. Authors: Kundu, M. R.; Liu, S. -Y. Bibcode: 1976SoPh...49..267K Altcode: A coronal hole was observed at 85 GHz(3.5 mm-λ) on November 24, 1970, when a spectacular coronal hole was observed in soft X-rays by AS&E. The millimeter counterpart of the hole is much weaker and less widespread than in X-rays. The brightness temperature inside the hole was in most places about 100-200 K lower than the mean brightness temperature of the Sun at 85 GHz. Title: Observations of intensity and linear polarization of CTB 80 at 6 and 2.8 cm. Authors: Velusamy, T.; Kundu, M. R.; Becker, R. H. Bibcode: 1976A&A....51...21V Altcode: The paper presents observations of the distribution of intensity and linear polarization over the radio source CTB 80 at 6 and 2.8 cm. The physical nature of the source is examined, particularly the relation between the strong central component and a ridgelike structure that extends across the northern half in the E-W direction. The structure, nonthermal spectrum, and polarization of the central component are found to be very similar to those of a supernova remnant, but the ridge is shown to be unlike any feature of any other SNR. It is suggested that the ridge may have resulted from expansion of the remnant shell into a dense interstellar cloud or, alternatively, that CTB 80 might be a nearby extragalactic radio source similar to Centaurus A. Title: 3.7 and 11.1 centimeter observations of the radio galaxy 3C 386. Authors: Becker, R. H.; Kundu, M. R. Bibcode: 1976ApJ...207...29B Altcode: We present radio observations of the radio galaxy 3C 386 at 3.7 and 11.1 centimeter wavelengths. The observations show that 3C 386 is composed of two extended components and a pointlike source midway between the two extended components which is coincident with an optical galaxy. The radio emission from the extended components is highly polarized. Subject headings: galaxies: individual - polarization - radio sources: extended Title: A decameter type II burst associated with a behind-the-limb flare. Authors: Gergely, T. E.; Kundu, M. R. Bibcode: 1976SoPh...48..357G Altcode: The characteristics of a decameter type II burst associated with a possible behind-the-limb flare are discussed. The burst source had an unusually high velocity. Assuming that the disturbance propagated as an MHD wave, the magnetic field strength at the 40 MHz plasma level is estimated to be 5.6 gauss. Title: High-resolution radio observations of three supernova remnants. Authors: Becker, R. H.; Kundu, M. R. Bibcode: 1976ApJ...204..427B Altcode: The paper presents and discusses radio observations of three supernova remnants (G21.5-0.9, G29.7-0.3, and 3C 391) made at 3.7 and 11.1 centimeters. The supernova remnant G21.5-0.9 has an elliptical brightness distribution and is similar to the Crab Nebula as well as 3C 58 in appearance and spectrum. The two remnants G29.7-0.3 and 3C 391 both show a broken shell structure typical of most galactic supernova remnants. Title: A Search for Radio Halos Around Pulsars Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1976ApL....17..177V Altcode: Observations of regions around 24 pulsars at 11, 21, and 40 cm are presented. Very extended sources have been observed close to the nearby pulsars 1642-03 and 1706-16. Double source structure with the pulsar on the line of separation has been found around four pulsars. The proper motions of pulsars 0823 + 26, 0834 + 06, 1133 + 16, and 2016 + 28 seem to be consistent with their possible association with the nearby continuum sources. The possibility that some of these sources may be radio halos or ghost remnants associated with the pulsars is discussed. Title: Differential rotation of the solar atmosphere as determined from millimeter data. Authors: Liu, S. -Y.; Kundu, M. R. Bibcode: 1976SoPh...46...15L Altcode: Radiospectroheliograms obtained at millimeter wavelengths were used to determine the rotation of the solar atmosphere. Regions observed in both emission as well as absorption (associated with Hα dark filaments) were followed across the disk. The average sidereal rotation rate deduced from emissive regions is given by ω (deg day-1)=14.152(±0.270)-4.194(±3.017)sin2B, where B is the heliographic latitude and the quoted errors are the standard deviations of a least squares fit to the data. The rate deduced from absorption regions is given by ω=14.729(±0.286)-1.050(±1.611)sin2B. This rate is larger than that of emissive regions at all latitudes and shows smaller differential rotation. This apparent difference in the rotation rates is probably due to the difference in the height of formation of the emissive and absorption regions. This difference could be used to estimate the difference in height between an emissive region and an absorption feature in millimeter radiation. Title: Observations of Jupiter's Radio Emission at 327 MHz and 1410 MHz During the Pioneer 11 Fly-By" Authors: Kundu, M. R.; Sarma, N. V. G.; Gerard, E. Bibcode: 1976ApL....18...41K Altcode: During the 1974 fly-by of Jupiter by the Pioneer 11 spacecraft, radio observations were carried out daily at 327 and 1410 MHz for a period of 60 days centered on December 3, 1974, the day of closest approach to Jupiter. The 1410-MHz data reveal two significant short-term variations in the Jovian radio emission; the largest one is probably present also at 327 MHz although Faraday rotation in earth's ionosphere could have affected the data. The two radio bursts appear to be correlated with two long-duration electron bursts observed in the energy ranges from 2 to 7 and 6 to 30 MeV. Title: On the Structure of Filaments from Centimeter and Millimeter Observations Authors: Butz, M.; Fuerst, E.; Hirth, W.; Kundu, M. R. Bibcode: 1975SoPh...45..125B Altcode: From filament observations at centimeter and millimeter wavelengths it is shown that the transition layer between the dense, cool filamentary material and the ambient hot, rarified corona is rather thin, of the order of some hundred kilometers. Hence, the difference in the sizes of filaments in the radio and optical domains is of the order of 1000 km or 2″, thus not detectable by the instruments so far used for observations of filaments. Title: A search for periodic variations of solar radio emission at 3.7- and 11.1-cm wavelengths. Authors: Kundu, M. R.; Alissandrakis, C. E. Bibcode: 1975MNRAS.173...65K Altcode: Periodic time variations in the emission of quiet solar regions were sought with the NRAO three-element interferometer at 3.7 and 11.1 cm. The visibility function of a source as obtained with a tracking interferometer is an implicit function of time, because of projected baseline changes, and therefore only observations taken when the baseline changes vary slowly with time were used. The visibility function shows significant time variations, but a power-spectrum analysis of the data revealed no unique periodicity. Title: Comments on the Quiet Sun Brightness Distribution at 1.2 mm Wavelength Authors: Kundu, M. R.; Liu, S. -Y. Bibcode: 1975SoPh...44..361K Altcode: A re-analysis of the brightness distribution of the quiet Sun at 1.2 mm wavelength is made. It is concluded that there is no evidence for uniform or limb-brightened distribution at this wave-length. Title: Observations at 6 CM of the solar active region Authors: Kundu, M. R.; Alissandrakis, C. E. Bibcode: 1975Natur.257..465K Altcode: Preliminary results are reported for the synthesis of a solar active region from observations with a synthesis radio telescope at a wavelength of 6 cm. Several individual sources are observed in the total-intensity and circular-polarization maps. These are shown to correspond to two large sunspots, two groups of small sunspots, and a plage. A magnetogram indicates that this active region had a bipolar structure with positive polarity concentrated on the main sunspots and negative polarity scattered over the plage and some of the small sunspots. It is noted that several radio bursts were recorded during the observation period and that one corresponded to a H-alpha flare near one of the sunspot groups. Title: Observations of nine supernova remnants at 10.6 GHz. Authors: Becker, R. H.; Kundu, M. R. Bibcode: 1975AJ.....80..679B Altcode: Intensity contour and polarization observation maps of nine supernova remnants at a microwave frequency are presented and discussed. The data provided are the highest-frequency (10.6 GHz) measurements to date for several of these sources and should therefore be useful in determining their spectra. Polarization ranges from 2 or 3% to as high as 40-50%. Integrated fluxes for the sources vary from about 3 to more than 25. Title: Depolarization of five supernova remnants: internal and external Faraday effects. Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1975A&A....41..307V Altcode: Summary. Depolarization in five supernova remnants Kes 69, W44, 1C443, 3Ct0 and 3C58 has been investigated using the polarization measured at 2.8, 6, t t and 2t cin with equivalent resolutions. The polarization data for certain regions in Kes 69, W 44 and IC 443 would be best interpreted if it were assumed that the depolarization is caused by an internal Faraday effect in the source. The physical parameters such as the internal and external rotation measures and the degree of inhomogeneity within the source have been derived from source models for internal depolarization. The sources Kes 69, W 44 and IC 443 seem to have large internal rotation measures and the rotation of the plane of polarization suggests deviations from the 2-law at long wavelengths. 3 C to and 3 C 58 have very small internal Faraday effects. A possibility of depolarization due to the observed variations of the external rotation measure across the remnants is also examined. In either case, the depolarization was found to be negligible at 2.8 cm in all these sources. When internal Faraday rotation effects are present, the frequently assumed 2-law for the rotation of the plane of polarization is found to be valid only for wavelengths shorter than a critical value which in turn depends on the amount of internal Faraday rotation in the source. Key words: supernova remnants linear polarization Faraday rotati6n depolarization Title: High Resolution Polarization Observations of a Solar Active Region at 6 cm. Authors: Alissandrakis, C. E.; Kundu, M. R. Bibcode: 1975BAAS....7..473A Altcode: No abstract at ADS Title: 6 cm Observations of A Solar Active Region with the Westerbork Synthesis Radio Telescope. Authors: Kundu, M. R.; Alissandrakis, C. E.; van Someren Greve, H. W. Bibcode: 1975BAAS....7..235K Altcode: No abstract at ADS Title: Decameter Storm Radiation, II Authors: Gergely, T. E.; Kundu, M. R. Bibcode: 1975SoPh...41..163G Altcode: The physical properties of six decametric storms, observed at Clark Lake Radio Observatory are studied. The height of the storm continuum sources was determined from the rotation rate. Assuming that the radiation originates at the plasma frequency we computed the gradient of electron density for the regions where the storms originate. The mean angular size of the decametric continuum sources is large; it increases with decreasing frequency. The storm continuum is found to be strongly directive toward the disk center. The east-west asymmetry, well observed at meter wavelengths is also observed at decameter wavelengths. Title: A Possible Relation Between z-Distribution and Spectral Index for Galactic Supernova Remnants. Authors: Becker, R. H.; Kundu, M. R. Bibcode: 1975BAAS....7R.247B Altcode: No abstract at ADS Title: High Resolution Observations of Solar Bursts at 3.7 and 11.1 cm Wavelengths Authors: Alissandrakis, C. E.; Kundu, M. R. Bibcode: 1975SoPh...41..119A Altcode: Four bursts were observed on August 9, 1973 with the NRAO 1 3-element interferometer at 3.7 and 11.1 cm. By using a simple source model we have calculated the temperature, flux, size and position of the small scale components of the bursts as a function of time. We obtained peak temperatures around 107 K for the components with size of about 10″ at 11.1 cm and 3″ at 3.7cm. The peak flux of these components lies between 4 and 40 % of the total peak flux of the bursts. Two of the bursts were found to be right circularly polarized. There is evidence that the location of these two bursts does not coincide with the location of the brightest point of the associated active regions. The existence of burst structures with temperatures of the order of 107K indicates that at least part of the radiation in these bursts is generated by a non-thermal mechanism. Title: Highly polarized radio outburst from Cygnus X-3. Authors: Seaquist, E. R.; Gregory, P. C.; Perley, R. A.; Becker, R. H.; Carlson, J. B.; Kundu, M. R.; Bignell, R. C.; Dickel, J. R. Bibcode: 1975JRASC..69...42S Altcode: No abstract at ADS Title: A possible relation between spectral index and z-distribution for supernova remnants. Authors: Becker, R. H.; Kundu, M. R. Bibcode: 1975A&A....38..149B Altcode: A statistical relation has been found between spectral index and the mean distance from the galactic plane for supernova remnants. Using z-distances calculated from the Sigma-D relationship and the observed spectral indices at radio frequencies for 93 galactic supernova remnants, the mean z-distance is found to vary from 175 pc to 60 pc for remnants with flat and steep spectra, respectively. A possible correlation between flat-spectra supernova remnants and pulsars is discussed. Title: Ghost remnants around pulsars. Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1975BASI....3R..35V Altcode: No abstract at ADS Title: Highly polarised radio outburst from Cygnus X-3 Authors: Seaquist, E. R.; Gregory, P. C.; Perley, R. A.; Becker, R. H.; Carlson, J. B.; Kundu, M. R.; Bignell, R. C.; Dickel, John R. Bibcode: 1974Natur.251..394S Altcode: WE report here the results of extensive observations of a new series of outbursts from Cyg X-3 which we commenced following the recent IAU telegram alert from Sir Martin Ryle. A high degree of linear polarisation has been discovered in one of the recent outbursts. The degree of polarisation changes over a period of 17 d and reaches a maximum of 14%. The observations indicate a high degree of order in the source magnetic field and that a thermal plasma coexists with the radiating relativistic electrons. In addition, a new upper limit of 0.05'' has been obtained for the angular size of Cyg X-3, together with an improved position for the source. Title: Polarization of supernova remnants: internal Faraday effects and derived magnetic fields. Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1974BASI....2...38V Altcode: No abstract at ADS Title: Observations of intensity and linear polarization in supernova remnants at 11 cm wavelength. Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1974A&A....32..375V Altcode: Summary. Distributions of intensity and linear polarization at 11 cm in twenty-four galactic sources in the northern sky are presented. The observations were made with angular resolution of 5' using the 300-ft. telescope of the National Radio Astronomy Observatory. Twenty sources were mapped in both total and polarized intensities and four were mapped in total intensity only The present maps at 11 cm have the highest resolution yet attained on many of these sources. Our results indicate that the galactic sources G 53.9+0.3, G 54.4-0.3, G 69.0+2.7 and G 93.4+1.8 are possible supernova remnants which until now are not listed as such in any of the catalogues. Observations of linear polarization at 6 cm in two sources, 3 C 434.1 and G 93.4+ 1.8, are also presented. The characteristics of the observed sources are discussed. Key words: supernova remnants - linear polarization Title: High Resolution Observations of Five Possible Supernova Remnants at Centimeter Wavelengths. Authors: Becker, R. H.; Kundu, M. R. Bibcode: 1974BAAS....6..313B Altcode: No abstract at ADS Title: Absence of Periodic Variation in Solar Radiation at 3.7 cm and 11.1 cm Wavelengths. Authors: Alissandrakis, C.; Kundu, M. R.; Becker, R. H. Bibcode: 1974BAAS....6..348A Altcode: No abstract at ADS Title: Meter and decameter wavelength positions of solar bursts of July 31 August 7, 1972 Authors: Kundu, M. R.; Erickson, W. C. Bibcode: 1974SoPh...36..179K Altcode: The positional analysis of solar bursts at meter and decameter wavelengths observed during the period July 31-August 7, 1972 is presented. Most of the activity during this period was associated with the active regions McMath 11976 and 11970. Except near the CMP of region 11976, two regions of continuum emission were observed - one a relatively smooth continuum and the other a continuum superimposed with many type III's and other fine structure. It seems possible to interpret these continua in terms of plasma waves originating from two sources located at different heights or with different electron density gradients. The angular size of type III sources seems to increase with decreasing frequency. This implies that the open field lines along which the type III electrons travel have larger angular extent at greater heights. Title: Observations of Coronal Disturbances from 1 to 9 Rsun. II: Second Event of 1973, January 11 Authors: Stewart, R. T.; Howard, R. A.; Hansen, F.; Gergely, T.; Kundu, M. Bibcode: 1974SoPh...36..219S Altcode: Observations of a coronal disturbance on 1973 January 11 commencing at 18h01m UT are described. The event is homologous with an earlier disturbance from the same region of the corona. The observations suggest that a cloud of coronal gas containing ∼ 4 × 1039 electrons propagated outwards to ⩾ 5 R⊙ behind a piston-driven shock wave travelling at a velocity of 800 to 1200 km s−1. Title: Polarization of supernova remnants KE 69, G 357.7-0.1, HC 26, and gamma Cygni at 6- and 2.8-cm wavelengths. Authors: Kundu, M. R.; Velusamy, T.; Hardee, P. E. Bibcode: 1974AJ.....79..132K Altcode: No abstract at ADS Title: Decameter Type IV Bursts Associated with Coronal Transients Authors: Gergely, T. E.; Kundu, M. R. Bibcode: 1974SoPh...34..433G Altcode: The characteristics of four moving type IV bursts, observed with the 65-20 MHz sweptfrequency interferometer of the Clark Lake Radio Observatory are discussed. All four bursts were associated with depletions in the electron content of the white light corona. Characteristics of the bursts are not unique, i.e. they differ in source size, structure, duration and their association with other radio bursts. Following Smerd and Dulk (1971) we believe that a shock wave, moving out from the flare site is responsible for the expansion of a magnetic arch or the ejection of a plasmoid which is observed as the usual type IV burst. Behind the shock wave, the compressed coronal gas moves outward, and as it expands it causes a depletion of electrons in the inner corona. After the passage of the shock wave, sometimes the coronal magnetic field structure is restored to its initial situation, as evidenced by the observation of homologous transients. Title: Meter and Decameter Wavelength Positions of Solar Radio Bursts of July 31-AUGUST 7, 1972 (presented by W.C. Erickson) Authors: Kundu, M. R.; Errickson, W. C. Bibcode: 1974IAUS...57..231K Altcode: No abstract at ADS Title: Long Base Line Interferometry of the Sun at 3.7 and 11.1 cm Wavelengths. Authors: Kundu, M. R.; Alissandrakis, C.; Becker, R. H. Bibcode: 1974BAAS....6..219K Altcode: No abstract at ADS Title: Fine Structure of a Solar Flare Region at 3.7 and 11.1 cm Wavelengths Authors: Kundu, M. R.; Velusamy, T.; Becker, R. H. Bibcode: 1974SoPh...34..217K Altcode: On June 9, 1973, a flare associated burst was observed with the NRAO 3-element interferometer at 3.7 and 11.1 cm wavelength. The burst was of `gradual rise and fall' type. Comparing the fringe amplitudes at 3.7 cm to the visibility computed for model flare regions we found that the precursor data are best fitted by a region of 3″ in size while at the time of the peak, the flare appears to have a size of 2″. During the post-maximum phase a size of 5″ is the best estimate. Similar computations have been done for 11.1 cm data. The peak brightness temperatures are 1.2 × 109 K and 1.65 × 108 K at 3.7 and 11.1 cm respectively. Such high temperatures would imply that a significant fraction of the burst radiation has a non-thermal origin. Title: Fine Structure of a Solar Active Region at 3.7 and 11.1 cm Wavelengths Authors: Kundu, M. R.; Becker, R. H.; Velusamy, T. Bibcode: 1974SoPh...34..185K Altcode: No abstract at ADS Title: Fine structure of the sun at centimeter wavelengths. Authors: Kundu, M. R.; Velusamy, T.; Becker, R. H. Bibcode: 1974IAUS...56...65K Altcode: No abstract at ADS Title: Long Base-Line Interferometry of the Sun at Centimeter Wavelengths Authors: Kundu, M. R. Bibcode: 1974cesra...4...21K Altcode: No abstract at ADS Title: Fine Structure of the Sun at 1.3 cm Wavelength Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1974SoPh...34..125K Altcode: The two-element interferometer at Hat Creek Observatory was used at 1.3 cm wavelength to study the fine structure of the radio emissive regions on the Sun. Observations of the quiet Sun at 1.3 cm show sudden changes in the fringe amplitude and phase, lasting for typically about 5-8 min. Assuming that these events are identical in nature, a plot of peak amplitude vs the projected baseline at the time of the event suggests emission from a region of angular size of about 10″. The corresponding brightness temperature is 50000 K. It is possible that these events may be related to the appearance and disappearance of groups of spicules or mottles. Title: Decameter Type IV Bursts Associated with Coronal Transients. Authors: Gergely, T. E.; Kundu, M. R. Bibcode: 1974BAAS....6..218G Altcode: No abstract at ADS Title: Polarization of Solar Active Regions at 3.5 Millimeter Wavelength Authors: Kuńdu, M. R.; Gergely, T. Bibcode: 1973SoPh...31..461K Altcode: A study of the circular polarization structure of solar active regions has been made from data obtained at 3.5 mm wavelength, using the 36 ft diameter radio telescope of the National Radio Astronomy Observatory at Kitt Peak, Arizona. The angular resolution of the telescope at this wavelength is 1'.2. All important active regions observed at 3.5 mm are bipolar in nature; the degree of polarization ranges from 1 to about 2%. These oppositely polarized components correspond with the Mt. Wilson magnetic regions of opposite polarity; the line of zero polarization delineates the neutral line between the regions of opposite polarity on magnetograms. The longitudinal magnetic fields at the level of 3.5 mm emission computed from the degree of polarization are found to be several hundred gauss. Title: Interferometric Measurements of the Compact Source 2048 + 31 Authors: Becker, R. H.; Kundu, M. R. Bibcode: 1973NPhS..244..138B Altcode: 1973Natur.244..138B OUR observations at 6 cm with a pencil beam of 6 arc min (ref. 1) and others at 11 and 3 cm with pencil beams of 4.8 and 1.2 arc min respectively (N. J. Keen, private communication) revealed a compact radio source several arc min north of the centre of the Cygnus Loop. The 3 cm observations failed to resolve the source, implying an angular size of less than 1 arc min. Title: Solar Active Regions at 9 and 3.5 mm Wavelengths under Disturbed Conditions Authors: Kundu, M. R.; Liu, Sou-Yang Bibcode: 1973SoPh...29..409K Altcode: Some properties of solar active regions at 9 and 3.5 mm wavelengths under disturbed conditions are discussed. New regions develop or weak regions intensify at millimeter wavelengths as a result of flares at distant sites. The spectra of the peak flux density of moderately strong bursts observed at 9 mm show a sharp drop toward the shorter millimeter wavelengths. The weak bursts at 3.5 mm manifest mainly as heating phenomena. Title: Polarization of the supernova remnant HB21 at 11-cm wavelength Authors: Kundu, M. R.; Becker, R. H.; Velusarny, T. Bibcode: 1973AJ.....78..170K Altcode: Linear polarization at 11-cm wavelength has been detected in the supernova remnant HB2 1. The degree of polarization varies from about 2% to as much as 20% in some regions. Comparison between the 11- and 6-cm wavelength polarization measurements yields the rotation measure, depolarization, and magnetic field distribu- tions over HB2 1. Over most of the remnant, the field appears to be the compressed interstellar field. The depolarization at 11 cm is primarily due to the steep gradient of the rotation measure. Large rotation measure appears to occur in regions of enhanced optical emission. Title: Observations of the HII region S101 in Cygnus Authors: Velusamy, T.; Kundu, M. R. Bibcode: 1973AJ.....78...31V Altcode: Observation of 5101 at 11- and 6-cm wavelengths with beams of 5 and 6 arcsec respectively, are presented. The physical parameters of the H II region have been deduced from the radio data. The excitation parameter of the central exciting star of spectral type O7 is 47 pc cm-2. Title: Millimeter Wavelength Observations of Solar Active Regions Authors: Kundu, M. R. Bibcode: 1973NASSP.342..104K Altcode: 1973heps.conf..104K No abstract at ADS Title: Polarization Structure of a Solar Flare Region at 9.5 mm Wavelength Authors: Kundu, M. R.; McCullough, T. P. Bibcode: 1972SoPh...27..182K Altcode: Polarization structure of an active region that produced a minor flare around 1900 UT on September 28, 1971 was measured at 9.5 mm wavelength using the 85-ft telescope of the Naval Research Laboratory Maryland Point Observatory. The angular resolution of the telescope at this wavelength is 1.6'. The flare region underwent changes both in the degree of polarization as well as in its polarization structure before and after the start of the flare. These changes in the degree of polarization correspond to a decrease of longitudinal magnetic field of about 200 G at the chromospheric levels where the 9.5 mm radiation originates. Observations on the polarization structure of active regions for several days before and after September, 1971 are also presented. Title: The Quiet Sun Brightness Distributions at Millimeter Wavelengths and Chro mospheric Inhomogeneities Authors: Lantos, P.; Kundu, M. R. Bibcode: 1972A&A....21..119L Altcode: Summary. The quiet sun brightness distributions at 9 and 3.5 mm wavelengths are presented. The distribution at 9 mm shows definite limb brightening whereas the distribution at 3.5 mm shows slight limb darkening. The distribution at 1.2 mm wavelength is known to exhibit definite limb darkening (Kundu, 1971). These distributions are interpreted in terms of a two-component chromospheric modeL Key words: sun - radiomillimetric wavelength - chromosphere - inhomogeneities Title: Brightness and polarization structure of four supernova remnants 3C 58, IC 443, W28, and W44 at 2.8 centimeter wavelength. Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1972A&A....20..237K Altcode: Summary. Distributions of brightness and polarization over four supernova remnants 3C58, IC443, W28 and W44 have been measured at 2.8 centimeter wavelength with a beam of 3'. Distributions of rotation measure over these sources have been computed by comparing the present data with the data at longer wavelengths. Significantly large variations of rotation measure over all the four sources have been observed. The rotation measure varies systematically over the sources 3C58 and W44. Possible origin of the Faraday rotation entirely in the interstellar medium outside the remnants is discussed. The distributions of the orientation of the projected magnetic field, derived from our data indicate very uniform orientation for the magnetic fields over both 3C58 and W44. There is no evidence for radial magnetic field in IC443. In W28, the projected magnetic field is tangential to the northern shell part of the remnant. The physical parameter for the remnants resulting from this study are given. Key words: supernova remnants - brightness - polarization Title: Observations of the Cygnus Loop at 6-cm Wavelength Authors: Kundu, M. R.; Becker, R. H. Bibcode: 1972AJ.....77..459K Altcode: Brightness and polarization distributions of the Cygnus Loop have been measured at 6-cm wavelength. Strong polarization of up to 25% has been observed throughout the source south of b =31 OO . Significant polarization has been detected in the northeastern shell region (NGC 6992-95). The derived magnetic-field distribution is found to be tangential to the southern boundary of the source, in agreement with previously published results. Title: Observations of Prominences at 3.5 Millimeter Wavelength Authors: Kundu, M. R. Bibcode: 1972SoPh...25..108K Altcode: At 3.5 mm wavelength absorption features are observed in correspondence with Hα dark filaments on the disk; beyond the limb the prominences correspond to emissive regions. The absorption features are larger (2'-3' arc) than the corresponding Hα dark filaments; the emissive regions at the limb have similar angular sizes. The emissive regions at the limb have electron temperatures of 5500±500 K; the amount of absorption observed on the disk leads to mean electron densities of about 5 × 1010 per cm3. Title: Polarization of Solar Active Regions at 9.5 mm Wavelength Authors: Kundu, M. R.; McCullough, T. P. Bibcode: 1972SoPh...24..133K Altcode: A study of the circular polarization structure of solar active regions has been made from data obtained at 9.5 mm wavelength, using the 85 ft reflector and polarimeter at the Naval Research Laboratory Maryland Point Observatory. The angular resolution of the telescope at this wavelength is 1'.6. All important active regions observed at 9.5 mm are bipolar in nature, the degree of polarization is about the same for both right and left circular components and it ranges up to about 4%. These oppositely polarized components correspond with the Mt. Wilson magnetic regions of opposite polarity; the line of zero polarization delineates clearly the neutral line between the regions of opposite polarity on magnetograms. Unipolar regions in magnetograms also show up as unipolar regions at 9.5 mm. Magnetic fields as low as 5-10 G on magnetograms manifest as distinctly polarized regions on 9.5 mm maps. A line of zero polarization seems to delineate the extent of `absorption features' observed at 9.5 mm in coincidence with Hα dark filaments. Title: Solar Radio Emission at 1.2 mm Wavelength Authors: Kundu, M. R. Bibcode: 1971SoPh...21..130K Altcode: Some properties of solar active regions at 1.2 mm wavelength are discussed. Equatorial and polar brightness distributions of the quiet Sun at 1.2 mm wavelength are also presented. Title: Structure of Non-thermal Radio Source G 55.7+3.4 in the Direction of CP1919 Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1971NPhS..234...54K Altcode: 1971Natur.234...54K Caswell and Goss1 have reported the detection of an extended radio source G55.7+3.4 at 2,700 and 178 MHz in the direction of the pulsar CP 1919, and because of its non-thermal spectrum they have proposed that it might be a galactic supernova remnant (SNR) associated with the pulsar. They pointed out, however, that the age (5 × 104 yr) and distance (7.5 kpc) of the assumed supernova remnant G55.7+3.4, calculated from its observed parameters, did not agree with those (age 107 yr and distance 300 to 1,800 pc) of the pulsar CP 1919 calculated from the observed period, its rate of slowing down, 21 cm absorption studies and dispersion measure. But1 these estimates are crude and consequently the apparent association should not be discarded as a chance coincidence. To investigate this apparent association further, we have mapped the region G55.7+ 3.4 at 11 and 21 cm wavelengths, with the 300 foot resurfaced telescope of the National Radio Astronomy Observatory. Title: Brightness and polarization structure of four supernova remnants at 2.8 centimeter wavelength. Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1971BAAS....3..499K Altcode: No abstract at ADS Title: Polarization of Solar Active Regions at 9 millimeter Wavelength Authors: Kundu, M. R.; McCullough, T. P. Bibcode: 1971BAAS....3R.449K Altcode: No abstract at ADS Title: Polarization of the Supernova Remnant HB 21 AT a Wavelength of 6 Centi-Meters Authors: Kundu, M. R. Bibcode: 1971ApJ...165L..55K Altcode: Linear polarization at 6-cm wavelength has been detected in the supernova remnant HB 21. The degree of polarization varies from about 10 percent to as much as 30 percent in some regions. A detailed comparison between the map at 6-cm wavelength obtained with a resolution of 6' of arc and the optical picture of the remnant shows that the general shape and boundary of the optical nebula correspond roughly with the outermost radio contours. Some bright radio spots within the remnant have diffuse optical nebulosities associated with them. Title: Polarization of Tycho's Supernova Remnant at a Wavelength of 2.8 Centimeters Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1971ApJ...163..231K Altcode: The polarized-brightness distribution for Tycho's supernova remnant has been obtained at a wavelength of 2.8 cm. The degree of linear polarization varies considerably over the source from 8 percent near the outer boundary to nearly zero at the center; the orientation of the electric vectors is circumferential. From a comparison of the 2.8-cm map with similar maps obtained at other wavelengths, the distributions of spectrum, rotation measure, and depolarization over the source have been studied. Title: Active Regions at Millimeter Wavelength and the Measurement of Magnetic Fields Authors: Kundu, M. R. Bibcode: 1971IAUS...43..642K Altcode: No abstract at ADS Title: Polarization of 3C10, 3C58 and several other radio sources at 2.8 Centimeter Wavelength Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1971BAAS....3...21K Altcode: No abstract at ADS Title: Solar Bursts at Decameter and Hectometer Wavelengths Authors: Kundu, M. R. Bibcode: 1971ASSL...27..287K Altcode: 1971psc..conf..287K No abstract at ADS Title: Positions and Motions of Solar Bursts at Decameter Wavelengths Authors: Kundu, M. R.; Erickson, W. C.; Jackson, P. D.; Fainberg, J. Bibcode: 1970SoPh...14..394K Altcode: The positions and motions of solar bursts in the range 20 to 60 MHz have been measured by the means of a sweep-frequency grating interferometer with angular resolution of 5' arc at 60 MHz decreasing to 15' arc at 20 MHz. The positional characteristics of the decameter wavelength bursts are discussed in terms of the commonly accepted theories of the origin of radio bursts from plasma and synchrotron radiations. Title: Brightness and Polarization Structure of Three Supernova Remnants at 6-AND 11-centimeter Wavelengths Authors: Kundu, M. R. Bibcode: 1970ApJ...162...17K Altcode: Distributions of brightness and polarization of three known supernova remnants Puppis A, W28, and PKS 1459-41 (S.N. 1006) have been measured at 6- and 11-centimeter wavelengths. Significant polarization has been detected in all three sources. The distribution of the derived magnetic fields has a tendency to be tangential to the rim on the shell side of the sources Pup A and W28, whereas it tends to be approximately radial for the supernova remnant of A.D. 1006. Title: Solar Active Regions at Millimeter Wavelengths Authors: Kundu, M. R. Bibcode: 1970SoPh...13..348K Altcode: Some properties of solar active regions at 9, 3.5 and 1.2 mm wavelengths are discussed. The regions have excess brightness temperatures of up to 1000, 700 and 150 K at 9, 3.5 and 1.2 mm wavelengths. The background radiation at 3.5 mm is often seen to be `absorbed' in regions closely coincident with Hα dark filaments on the disk. Interpretation of this `absorption' as due to the large optical thickness of the overlying filamentary material leads to an estimate of electron density in the filaments. The 9 and 3.5 mm-λ regions show almost one-to-one correspondence with the Ca-plage regions as well as with the regions on magnetograms. The latter relationship suggests the possibility of measuring chromospheric magnetic fields from the measurement of polarization at millimeter wavelengths. Title: The Slowly Varying Component of the Sun's Radiation at Millimeter Wavelengths Authors: Kundu, M. R. Bibcode: 1970BAAS....2T.203K Altcode: No abstract at ADS Title: Polarization of the Cygnus Loop at 11-CENTIMETER Wavelength Authors: Kundu, M. R. Bibcode: 1969ApJ...158L.103K Altcode: No abstract at ADS Title: Polarized Brightness Distributions of Supernova Remnants IC 443 and W44 at 6-CM Wavelength Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1969ApJ...155..807K Altcode: Polarized brightness distributions of two supernova remnants, IC 443 and W44, have been deter- mined at 6-cm wavelength, from observations made with a resolution of 6', by using the 140-foot reflector of the National Radio Astronomy Observatory. Both IC 443 and W44 are partially linearly polarized at 6-cm wavelength. The degree of polarization and orientation of electric vectors are different at different parts of IC 443. Over its southeastern rim, the degree of polarization is large, about 4.5 per cent, and the orientation of electric field is largely tangential. Over its northeastern peak, the degree of polarization is low, and the field orientation is random. The distribution of polarized brightness in W44 is broadly similar to that of total intensity. The peak of linearly polarized radiation roughly coincides with the peak of total intensity, and the electric field has a systematic alignment with a position angle of 400 over the main peak as well as over the eastern region. The degree of polarization is negligibly small over the peak of the isolated source situated to the west of W44 around a = 18h50m528 and ô = O1°11'30", which indicates that it is thermal in nature Title: Polarized Brightness Distributions of Supernova Remnants IC 443 W44, and the Cygnus Loop at 6- and 11-cm Wavelengths Authors: Kundu, M. R. Bibcode: 1969BAAS....1R.197K Altcode: No abstract at ADS Title: Possible Interpretation of Pulses from a Radio Source Authors: Kundu, M. R.; Chitre, S. M. Bibcode: 1968Natur.218.1037K Altcode: THE Cambridge group1 recently announced the recording of pulses from a local object, lasting for about 0.016 s and repeating with extreme regularity with a period of 1.337 s, the accuracy being one part in 107. There have been further observations from Cambridge2 and from Jodrell Bank3. The amplitude of the pulses varies randomly, the pulses appearing and disappearing for periods of a few minutes. There is also a fine structure superimposed on the main pulse. Despite the regularity of the pulses, the power emitted varies significantly over all periods. Furthermore, observations indicate a frequency drift of -5 MHz s-1. The absence of any proper motion of the source, and the interpretation of the frequency drift in terms of dispersion through the interstellar plasma, limit the distance of the source to the range 103 A.U. <d<65 pc. An eighteenth magnitude blue stellar object has been found near the object, although there seems to be uncertainty about the nature of the object. From the pulse width and the rate of frequency drift the source is smaller than 5 × 108 cm. Title: Lunar Occupation of a Solar Active Region at 4 cm Wavelength Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1968Natur.217.1132K Altcode: THE solar eclipse of July 20, 1963, was observed from Ann Arbor, Michigan, using the 85 ft. paraboloid telescope of the University of Michigan. As observed from Michigan the solar eclipse was partial; however, the Moon completely occulted two discrete regions on the Sun-one near the east limb and the other near the west limb. We observed the lunar occultation of the eastern region. At the 4 cm wavelength at which this occultation was observed, the pencil beam of the radio telescope had a half-power width of 5'.95 of arc. Drift scans were taken across the region before the occultation in order to find the position of the peak. These scans indicated an angular size of about 3' of arc and a position which was in agreement with the position indicated by Stanford λ 9.1 cm maps. Thus the beam almost completely covered the discrete region, and the observations consisted in tracking the region throughout the period of occultation with the beam pointed on the peak of the region. The occultation was observed in both immersion and emersion. Title: Solar Radio Astronomy Authors: Kundu, Mukul R. Bibcode: 1968SvA....11..733K Altcode: No abstract at ADS Title: Radio spectra of the nebula IC443 Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1968MNRAS.140..173K Altcode: Combining our observations at 430 and 195 MHz with pencil beams of 17' and 35' arc respectively with other high resolution observations at 750, 1400, 3000 and 5000 MIIz, the flux density spectrum over different regions of the shell source IC443 has been computed. It appears that the north-east bright rim or shell has a curved spectrum with spectral index of and below and above 750 MHz. The other regions exhibit a straight line spectrum with spectral index of about . Title: Some Properties of the Sources of Slowly Varying Component and of Bursts at 612 MC S Authors: Swarup, G.; Kundu, M. R.; Kapahi, V. K.; Isloor, J. D. Bibcode: 1968IAUS...35..581S Altcode: No abstract at ADS Title: A study of the Cygnus loop at 430, 195 and 41 MHz Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1967AnAp...30..723K Altcode: No abstract at ADS Title: A study of galactic sources W 51 and W 44 Authors: Kundu, M. R.; Velusamy, T. Bibcode: 1967AnAp...30...59K Altcode: No abstract at ADS Title: Solar Radio Astronomy Authors: Kundu, Mukul R. Bibcode: 1967AZh....44..910K Altcode: No abstract at ADS Title: Buchbesprechungen über: Solar Radio Astronomy. (Ref. A. UNSÖLD) Authors: Kundu, M. R. Bibcode: 1967ZA.....66..339K Altcode: No abstract at ADS Title: Review of Publications- Solar Radio Astronomy Authors: Kundu, Mukul R. Bibcode: 1966JRASC..60..296K Altcode: No abstract at ADS Title: Solar Radio Astronomy Authors: Kundu, Mukul R. Bibcode: 1966AmJPh..34..829K Altcode: No abstract at ADS Title: Lunar Occultation of the Radio Sources 0938 + 18 and 1101 + 11 Authors: Cohen, M. H.; Kundu, M. R. Bibcode: 1966ApJ...143..621C Altcode: The radio sources 0938 + 18 and 1101 + 11 have been observed at 430 MHz during the immersion phase of a lunar occultation. The source 0938 + 18 is a single source of diameter 4"; 1101 + 11 is a double source with approximately equal components separated by 9'.'4. The Palomar 8ky 8urvey pnnts show a faint bk object near 0938 + 18, and show no optical object at the position of 1101 + 11. Title: Occultation of Taurus-A by the Solar Corona at 430 Mc/s in June 1964 Authors: Kundu, M. R. Bibcode: 1965Natur.205..683K Altcode: DURING June of every year, the radio source Taurus-A passes within a small angular distance of the Sun. This particular situation, commonly referred to as the occultation of Taurus-A by the Sun, permits an investigation of the Sun's outer corona as the radio source is viewed through it. The measurements made over the past several years have demonstrated that the radiation from the source is scattered at the electron density irregularities in the corona; as a result one observes an apparent broadening of the source accompanied by a decrease of its intensity. The effect becomes larger with decreasing angular separation of the source from the Sun. This phenomenon has been observed in the range of frequencies 26-178 Mc/s1-5. At wave-lengths of 6 and 18 cm the effect has been reported to be negative6,7, except that a positive result has been reported on 10- and 25-cm wave-lengths8. The results on all metre and decametre wave-lengths are consistent and are in accordance with the theory of small-angle multiple scattering, in which the angular size of the scattered distribution is proportional to the square of the wave-length. However, the increase of intensity on 169 Mc/s at 7 R0 (R0 is the photospheric radius) from the centre of the Sun is not consistent with the theoretical prediction based on the lower frequency data5. In order to investigate if the coronal scattering is still effective at frequencies higher than 169 Mc/s, and in particular to see if the increase of intensity is also observed on 430 Mc/s, we undertook to observe at 430 Mc/s the occultation of Taurus-A by the solar corona in June 1964, using the 1,000-ft. dish of the Arecibo Ionospheric Observatory. Title: Some Aspects of the Type-IV Continuum Radiation on Decimeter Wave-lengths Authors: Kundu, M. R. Bibcode: 1965ASSL....1..408K Altcode: 1965sosp.conf..408K No abstract at ADS Title: Solar radio astronomy Authors: Kundu, Mukul R. Bibcode: 1965sra..book.....K Altcode: 1965QB521.K9....... No abstract at ADS Title: A Survey of the Interpretations of Radio and X-Ray Bursts Authors: Kundu, M. R. Bibcode: 1964NASSP..50..335K Altcode: 1964psf..conf..335K No abstract at ADS Title: Centimeter-Wave Radio and X-Ray Emission from the Sun Authors: Kundu, M. R. Bibcode: 1963SSRv....2..438K Altcode: No abstract at ADS Title: Spectral Characteristics of Solar Continuum Radiation in the 500-1000 Mc/s Range. Authors: Kundu, M. R.; Spencer, C. L. Bibcode: 1963ApJ...137..572K Altcode: The spectral characteristics of flare-associated continuum radiation in the S()(} 1O()() Mc/s range are described. The continuum radiation in this frequency range consists of a smooth background continuum and different variabilities superimposed upon it. The superimposing variabilities are mostly in the form of fine structure fast-drift bursts; however, occasionally they appear in the form of "sprays" or patchiness. The meter-X type IV continuum radiation is always associated with a dcm-X burst of continuum radiation. The dcm-X continuum starts almost simultaneously as the concurrent cm-X continuum; also, its maxima sometimes correspond to the cm-X maxima. From these and other characteristics (such as source sixe, height, motion, etc.) of dcm-X continuum, it is suggested that the dcm-X continuum, like the concurrent cm-X continuum, represents the first phase of type IV radiation as a whole. Only a small fraction of meter- bursts of spectral types II and V are associated with dcm-X bursts. The type II associated dcm-X bursts are mostly of continuum type, although fast-drift elements may sometimes be superim,posed "generalixed fast-drift' type. on the continuum. The type V associated dcm-X bursts are mostly of Title: A Note on Bursts of Radio Emission and High Energy (>20 keV) X-Rays from Solar Flares Authors: De Jager, C.; Kundu, M. R. Bibcode: 1963spre.conf..836D Altcode: No abstract at ADS Title: Association of Centimeter-Wave Bursts with Different Spectral Types of Meter-Wave Burst of Solar Radio Emission Authors: Kundu, M. R. Bibcode: 1962JGR....67.2695K Altcode: It is shown that about 40 per cent of 10.7 cm-λ bursts with peak intensities greater than 5×10-22 wm-2 (c/s)-1 are accompanied by bursts on meter waves. The percentage association increases with the peak intensity of 10.7 cm-λ bursts and attains a value of about 90 per cent when the peak intensity exceeds 1000×10-22 wm-2 (c/s)-1. The reverse association, that is, the association of a meter-λ burst with a burst on centimeter waves, is dependent on the spectral type of the meter-λ burst. The association is about 15, 40, 70, and 100 per cent for types III, V, II, and IV, respectively. The type III and type V bursts usually occur within about 1 minute and ½ minute, respectively, of the associated cm-λ burst maxima. The type II bursts occur after about 2 to 6 minutes of the associated cm-λ burst maxima. The type IV bursts in the 250 to 580 Mc/s range occur within about 4 minutes of the start of the associated cm-λ bursts. From simultaneous dynamic spectral observations in the 25 to 580 Mc/s range and single-frequency observations on 9400, 3750, 2000, and 1000 Mc/s, the average spectra of cm-λ bursts associated with different spectral types of meter-λ bursts have been studied. It is shown that cm-λ bursts associated with meter-λ type IV and type II bursts have brightness temperatures of the order of 108 and 107 deg K, respectively, and can probably be explained by synchrotron radiation of high-energy electrons. The cm-λ bursts associated with type V and type III bursts have brightness temperatures of 106 to 107 deg K in the 2000 to 9400 Mc/s range and have probably a thermal plus synchrotron origin; the 1000 Mc/s bursts have brightness temperatures higher than 107 deg K and have a nonthermal origin, probably due to plasma oscillation corresponding to type III bursts. The cm-λ bursts unaccompanied by any meter-λ burst have brightness temperatures less than 106 deg K and are believed to have a thermal origin. Title: Some Relations between Centimeter-Wave Radio Bursts and Solar Cosmic Rays and X-Rays Authors: Kundu, M. R. Bibcode: 1962JPSJS..17B.259K Altcode: 1962ICRC....7B.259K; 1962PSJaP..17B.259K; 1962JPSJ...17B.259K No abstract at ADS Title: The Nature of Type IV Solar Radio Bursts Authors: Kundu, M. R. Bibcode: 1962JPSJS..17B.215K Altcode: 1962ICRC....7B.215K; 1962PSJaP..17B.215K; 1962JPSJ...17B.215K No abstract at ADS Title: Bursts of Centimeter-Wave Emission and the Region of Origin of X Rays from Solar Flares Authors: Kundu, M. R. Bibcode: 1961JGR....66.4308K Altcode: High energy (>20 kev) solar X-ray emission during flares has been measured with the help of rockets and balloons by various workers [Chubb, Friedman, and Kreplin, 1960; Winckler, May, and Masley, 1961; Peterson and Winckler, 1959; Vette and Casal, 1961]. The observation of X rays in the quantum energy range 20 to 70 kev during three flares accompanied by SID's led Friedman to suggest that the presence of such X rays was characteristic of the flare process. The 20 to 70 kev X rays appeared as an extension of the high intensity flux of 2 to 10 A X rays, which are the main components responsible for flare time enhanced D-layer ionization (SID). It has been shown statistically by Dodson, Hedeman, and Covington [1954], Hachenberg and Krüger [1960], and Kawabata [1961] that centimeter-wave bursts are closely associated with SID's. Title: Interferometric Studies of Type IV Solar Bursts of Continuum Radiation on 340 and 87 Mc/s. Authors: Kundu, M. R.; Firor, J. W. Bibcode: 1961ApJ...134..389K Altcode: Interferometric observations made on 340 and 87 Mc/s show the following properties of Type IV continuum bursts: (1) Type IV emission on 340 Mc/s occurs at a height of less than 40000 km in the solar atmosphere. Its source has a small angular diameter (usually less than 4'), and it shows practically no motion within +2 minutes of arc. (2) Type IV emission on 87 Mc/s occurs high in the corona (more than 200000 km above the photosphere). Its source has a large angular diameter (of the order of 10' or larger) and a large movement. These distinctive properties of Type IV emission as observed on 340 and 87 Mc/s support the suggestion that Type IV emission occurs in two distinct phases-one characteristic of centimeter-wave continuum emission extending up to frequencies as low as 250 Mc/s, and the other, characteristic of meter-wave continuum emission occurring at frequencies lower than about 250 Mc/s. Title: Some Studies on the Occurrence of Type IV Solar Bursts of Continuum Radiation. Authors: Kundu, M. R. Bibcode: 1961AJ.....66..289K Altcode: It is shown that type IV emission in the range of frequencies 25-580 Mc occurs in two distinct phases: (a) the first phase, usually observed at frequencies higher than about 250 Mc, appears to be an extension of the associated centimeter-wave burst which is also a broad-band continuum emission. This emission occurs earlier than the associated type II burst and can even occur independent of any type II burst. The source of this emission is situated low in the chromosphere, has no significant movement and has a small angular size, usually less than 4'. The observed properties of this phase of continuum emission are consistent with the suggestion that it it is caused low in the chromosphere by synchrotron radiation of electrons generated during the flare. (b) The second phase, usually observed at frequencies lower than about 250 Mc, is closely associated with a type II burst preceding it. The source of this continuum emission is situated high in the corona and moves with velocities of more than 1000 km/sec. It has a large angular size, usually 10' or larger. This second phase of type IV emission was previously explained as due to synchrotron radiation of electrons higher in the corona, when a cloud of gas with a shock front (which excites the type II burst) moving at high velocities carries a frozen-in magnetic field to the appropriate heights in the corona. Title: Some Studies on the Occurrence of Type IV Solar Bursts of Continuum Radiation. Authors: Kundu, M. R. Bibcode: 1961ApJ...134...96K Altcode: It is shown that type IV emission in the range of frequencies 25-580 Mc/s occurs in two distinct phases: (a) The first phase, usually observed at frequencies higher than about 250 Mc/s, appears to be an extension of the associated centimeter-wave burst which is also a broad-band continuum emission. This emission occurs earlier than the associated type II burst and can even occur independent of any type II burst. The source of this emission is situated low in the chromosphere, has no significant movement, and has a small angular size, usually less than 4'. The observed properties of this phase of continuum emission are consistent with the suggestion that it is caused low in the chromosphere by synchrotron radiation of electrons generated during the flare. (b) The second phase, usually observed at frequencies lower than about 250 Mc/s, is closely associated with a type II burst preceding it. The source of this continuum emission is situated high in the corona and moves with velocities of more than 1000 km/sec. It has a large angular size, usually 10' or larger. This second phase of type IV emission was previously explained as due to synchrotron radiation of electrons higher in the corona, when a cloud of gas with a shock front (which excites the type II burst) moving at high velocities carries a frozen-in magnetic field to the appropriate heights in the corona. Title: A Comparison of the Dynamic Spectra of Solar Radio Bursts in the Decimeterand Meter-Wave Ranges. Authors: Kundu, M. R.; Roberts, J. A.; Spencer, C. L.; Kuiper, J. W. Bibcode: 1961ApJ...133..255K Altcode: The existence of two classes of fast-drift (Type III) bursts is recognized from a comparison of the dynainic spectra of solar radio bursts observed at the University of Michigan in the 100-580 Mc/s range and, in some cases, in the 20004000 Mc/s range and at Convair-Caltech in the 500-950 Mc/s range One class corresponds to the meter-wave-length bursts and predominantly extend to the low-frequency edge of the records at 100 Mc/s a nd the other to the decimeter-t ype bursts which are observed to terminate mainly above 400 Mc/s and typically between 400 and 550 Mc/s An example is given of an event in which the 500-950 Mc/s range shows a short continuum increase in time coincidence with a group of meter-wave-length Type III bursts preceding a Type II burst. Another example of a similar event shows that the continuum increase exists at higher frequencies f <2000 to >4000 Mc/s) Title: Solar Radio Emission on Centimeter Waves and Ionization of the E Layer of the Ionosphere Authors: Kundu, M. R. Bibcode: 1960JGR....65.3903K Altcode: It is shown that solar radio emission on any wavelength shorter than 30 cm is good as a solar index for ionospheric studies. The coefficient of correlation between E-layer ionization index and solar radiation decreases to a low value for wavelengths greater than about 30 cm, indicating that a major part of solar X radiation responsible for E-layer ionization originates in the solar atmosphere below the height of origin of 30-cm solar radio emission. Title: A Relation Between Solar Radio Emission and Polar Cap Absorption of Cosmic Noise Authors: Kundu, M. R.; Haddock, F. T. Bibcode: 1960Natur.186..610K Altcode: No abstract at ADS Title: Structures et propriétés des sources d'activit&eacute solaire sur ondes centimétriques Authors: Kundu, M. R. Bibcode: 1959AnAp...22....1K Altcode: No abstract at ADS Title: Etude interférométrique des sources d'activité solaire sur 3 CM de longueur d'onde Authors: Kundu, M. R. Bibcode: 1959IAUS....9..222K Altcode: No abstract at ADS