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Author name code: kasparova
ADS astronomy entries on 2022-09-14
author:Kasparova, Jana
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Title: Filament Leg--Leg Reconnection as a Source of Prominent
Supra-Arcade Downflows
Authors: Dudik, Jaroslav; Aulanier, Guillaume; Kasparova, Jana;
Karlicky, Marian; Zemanova, Alena; Lorincik, Juraj; Druckmuller,
Miloslav
2022arXiv220900306D Altcode:
We report on interaction of the legs of the erupting filament
of 2012 August 31 and associated prominent supra-arcade downflows
(P-SADs) as observed by the Atmospheric Imaging Assembly onboard the
Solar Dynamics Observatory. We employ a number of image processing
techniques to enhance weak interacting features. As the filament erupts,
both legs stretch outwards. The positive-polarity leg also untwists
and splits into two parts. The first part runs into the conjugate
(negative-polarity) leg, tearing it apart. The second part then
converges into the remnant of the conjugate leg, after which both
weaken and finally disappear. All these episodes of interaction of
oppositely-oriented filament legs are followed by appearance of P-SADs,
seen in the on-disk projection to be shaped as loop-tops, along with
many weaker SADs. All SADs are preceded by hot supra-arcade downflowing
loops. This observed evolution is consistent with the three-dimensional
rr-rf (leg-leg) reconnection, where the erupting flux rope reconnects
with itself. In our observations, as well as in some models, the
reconnection in this geometry is found to be long-lasting. It plays
a substantial role in the evolution of the flux rope of the erupting
filament and leads to prominent supra-arcade downflows.
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Title: A first comparison of FLARIX flare simulations with the MSDP
H-alpha spectral observations on very short time scales
Authors: Heinzel, Petr; Kasparova, Jana; Berlicki, Arkadiusz;
Radziszewski, Krzysztof; Rudawy, Pawel
2022cosp...44.2560H Altcode:
We present first results of a comparative analysis of high temporal
resolution MSDP H$\alpha$ observations of a compact solar flare with
results of radiation-hydrodynamical simulations performed using the
FLARIX code. X-ray spectral observations of a compact C1 GOES-class
flare obtained from RHESSI satellite were used to estimate physical
parameters of the electron beams transporting the energy from the
reconnection site down to the chromosphere. These parameters are then
used for data-driven FLARIX simulations. A small size of the flare
and its simple structure allowed us to assume a single-loop geometry
which significantly simplified the modelling and analysis of the
whole event. Using the MSDP imaging spectrograph at Bia{\l}k\'{o}w
observatory, it was possible to compare the recorded H$\alpha$
line emission with that obtained from FLARIX simulations, on short
time-scales down to 50 ms.
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Title: Narrowband Spikes Observed During the 13 June 2012 Flare in
the 800 - 2000 MHz Range
Authors: Karlický, Marian; Rybák, Ján; Benáček, Jan; Kašparová,
Jana
2022SoPh..297...54K Altcode: 2022arXiv220409327K
Narrowband (∼5 MHz) and short-lived (∼0.01 s) spikes with three
different distributions in the 800 - 2000 MHz radio spectrum of the
13 June 2012 flare are detected and analyzed. We designate them as SB
(spikes distributed in a broad band or bands), SZ (spikes distributed
in zebra-like bands) and SBN (spikes distributed in broad and narrow
bands). On analyzing AIA/SDO images of the active region NOAA 11504,
a rough correspondence between groups of the spikes observed at 1000
MHz and peaks in the time profiles of AIA channels taken from the
flare subarea close to the leading sunspot is found. Among the types
of spikes the SZ type is the most interesting because it resembles
zebras. Therefore, using autocorrelation and crosscorrelation methods
we compare SZ and SBN spikes with the typical zebra observed in the
same frequency range. While the ratio of SZ band frequencies with their
frequency separation (220 MHz) is about 4, 5, and 6, in the zebra the
frequency stripe separation is about 24 MHz and the ratio is around
50. Moreover, the bandwidth of SZ bands, which consists of clouds of
narrowband spikes, is much broader than that of zebra stripes. This
comparison indicates that SZ spikes are generated in a different way
from the zebra, but in a similar way to SBN spikes. We successfully fit
the SZ band frequencies by the Bernstein modes. Based on this fitting
we interpret SZ and SBN spikes as those generated in the model of
Bernstein modes. Thus, the magnetic field and plasma density in the SZ
spike source are estimated to be about 79 G and 8.4 × 10<SUP>9</SUP>
cm<SUP>−3</SUP>, respectively.
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Title: STIX X-ray microflare observations during the Solar Orbiter
commissioning phase
Authors: Battaglia, Andrea Francesco; Saqri, Jonas; Massa, Paolo;
Perracchione, Emma; Dickson, Ewan C. M.; Xiao, Hualin; Veronig,
Astrid M.; Warmuth, Alexander; Battaglia, Marina; Hurford, Gordon J.;
Meuris, Aline; Limousin, Olivier; Etesi, László; Maloney, Shane A.;
Schwartz, Richard A.; Kuhar, Matej; Schuller, Frederic; Senthamizh
Pavai, Valliappan; Musset, Sophie; Ryan, Daniel F.; Kleint, Lucia;
Piana, Michele; Massone, Anna Maria; Benvenuto, Federico; Sylwester,
Janusz; Litwicka, Michalina; Stȩślicki, Marek; Mrozek, Tomasz;
Vilmer, Nicole; Fárník, František; Kašparová, Jana; Mann,
Gottfried; Gallagher, Peter T.; Dennis, Brian R.; Csillaghy, André;
Benz, Arnold O.; Krucker, Säm
2021A&A...656A...4B Altcode: 2021arXiv210610058B
Context. The Spectrometer/Telescope for Imaging X-rays (STIX) is the
hard X-ray instrument onboard Solar Orbiter designed to observe solar
flares over a broad range of flare sizes. <BR /> Aims: We report
the first STIX observations of solar microflares recorded during
the instrument commissioning phase in order to investigate the STIX
performance at its detection limit. <BR /> Methods: STIX uses hard
X-ray imaging spectroscopy in the range between 4-150 keV to diagnose
the hottest flare plasma and related nonthermal electrons. This first
result paper focuses on the temporal and spectral evolution of STIX
microflares occuring in the Active Region (AR) AR12765 in June 2020,
and compares the STIX measurements with Earth-orbiting observatories
such as the X-ray Sensor of the Geostationary Operational Environmental
Satellite (GOES/XRS), the Atmospheric Imaging Assembly of the Solar
Dynamics Observatory, and the X-ray Telescope of the Hinode mission. <BR
/> Results: For the observed microflares of the GOES A and B class, the
STIX peak time at lowest energies is located in the impulsive phase of
the flares, well before the GOES peak time. Such a behavior can either
be explained by the higher sensitivity of STIX to higher temperatures
compared to GOES, or due to the existence of a nonthermal component
reaching down to low energies. The interpretation is inconclusive
due to limited counting statistics for all but the largest flare
in our sample. For this largest flare, the low-energy peak time is
clearly due to thermal emission, and the nonthermal component seen at
higher energies occurs even earlier. This suggests that the classic
thermal explanation might also be favored for the majority of the
smaller flares. In combination with EUV and soft X-ray observations,
STIX corroborates earlier findings that an isothermal assumption
is of limited validity. Future diagnostic efforts should focus on
multi-wavelength studies to derive differential emission measure
distributions over a wide range of temperatures to accurately describe
the energetics of solar flares. <BR /> Conclusions: Commissioning
observations confirm that STIX is working as designed. As a rule of
thumb, STIX detects flares as small as the GOES A class. For flares
above the GOES B class, detailed spectral and imaging analyses can
be performed.
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Title: On the importance of Ca II photoionization by the hydrogen
lyman transitions in solar flare models
Authors: Osborne, C. M. J.; Heinzel, P.; Kašparová, J.; Fletcher, L.
2021MNRAS.507.1972O Altcode: 2021MNRAS.tmp.1947O; 2021arXiv210711145O
The forward fitting of solar flare observations with
radiation-hydrodynamic simulations is a common technique for learning
about energy deposition and atmospheric evolution during these explosive
events. A frequent spectral line choice for this process is Ca II
854.2 nm due to its formation in the chromosphere and substantial
variability. It is important to ensure that this line is accurately
modelled to obtain the correct interpretation of observations. Here,
we investigate the importance of photoionization of Ca II to Ca III by
the hydrogen Lyman transitions, whilst the Lyman continuum is typically
considered in this context in simulations, the associated bound-bound
transitions are not. This investigation uses two RADYN flare simulations
and reprocesses the radiative transfer using the Lightweaver framework
which accounts for the overlapping of all active transitions. The
Ca II 854.2 nm line profiles are found to vary significantly due to
photoionization by the Lyman lines, showing notably different shapes
and even reversed asymmetries. Finally, we investigate to what extent
these effects modify the energy balance of the simulation and the
implications on future radiation-hydrodynamic simulations. There
is found to be a 10-15 per cent change in detailed optically thick
radiative losses from considering these photoionization effects on
the calcium lines in the two simulations presented, demonstrating the
importance of considering these effects in a self-consistent way.
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Title: Flare Expansion to a Magnetic Rope Accompanied by Rare
Radio Bursts
Authors: Zemanová, Alena; Karlický, Marian; Kašparová, Jana;
Dudík, Jaroslav
2020ApJ...905..111Z Altcode: 2021arXiv210108633Z
We present multispectral analysis (radio, Hα, ultraviolet (UV)/extreme
ultraviolet (EUV), and hard X-ray) of a confined flare from 2015 March
12. This flare started within the active region NOAA 12 297 and then it
expanded into a large preexisting magnetic rope embedded with a cold
filament. The expansion started with several brightenings located
along the rope. This process was accompanied by a group of slowly
positively drifting bursts in the 0.8-2 GHz range. The frequency drift
of these bursts was 45-100 MHz s<SUP>-1</SUP>. One of the bursts had an
S-like form. During the brightening of the rope we observed a unique
bright EUV structure transverse to the rope axis. The structure was
observed in a broad range of temperatures and it moved along the rope
with the velocity of about 240 km s<SUP>-1</SUP>. When the structure
dissipated, we saw a plasma further following twisted threads in the
rope. The observed slowly positively drifting bursts were interpreted
considering particle beams and we show that one with the S-like
form could be explained by the beam propagating through the helical
structure of the magnetic rope. The bright structure transverse to
the rope axis was interpreted considering line-of-sight effects and
the dissipation-spreading process, which we found to be more likely.
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Title: The Spectrometer/Telescope for Imaging X-rays (STIX)
Authors: Krucker, Säm; Hurford, G. J.; Grimm, O.; Kögl, S.;
Gröbelbauer, H. -P.; Etesi, L.; Casadei, D.; Csillaghy, A.; Benz,
A. O.; Arnold, N. G.; Molendini, F.; Orleanski, P.; Schori, D.; Xiao,
H.; Kuhar, M.; Hochmuth, N.; Felix, S.; Schramka, F.; Marcin, S.;
Kobler, S.; Iseli, L.; Dreier, M.; Wiehl, H. J.; Kleint, L.; Battaglia,
M.; Lastufka, E.; Sathiapal, H.; Lapadula, K.; Bednarzik, M.; Birrer,
G.; Stutz, St.; Wild, Ch.; Marone, F.; Skup, K. R.; Cichocki, A.; Ber,
K.; Rutkowski, K.; Bujwan, W.; Juchnikowski, G.; Winkler, M.; Darmetko,
M.; Michalska, M.; Seweryn, K.; Białek, A.; Osica, P.; Sylwester, J.;
Kowalinski, M.; Ścisłowski, D.; Siarkowski, M.; Stęślicki, M.;
Mrozek, T.; Podgórski, P.; Meuris, A.; Limousin, O.; Gevin, O.; Le
Mer, I.; Brun, S.; Strugarek, A.; Vilmer, N.; Musset, S.; Maksimović,
M.; Fárník, F.; Kozáček, Z.; Kašparová, J.; Mann, G.; Önel,
H.; Warmuth, A.; Rendtel, J.; Anderson, J.; Bauer, S.; Dionies, F.;
Paschke, J.; Plüschke, D.; Woche, M.; Schuller, F.; Veronig, A. M.;
Dickson, E. C. M.; Gallagher, P. T.; Maloney, S. A.; Bloomfield, D. S.;
Piana, M.; Massone, A. M.; Benvenuto, F.; Massa, P.; Schwartz, R. A.;
Dennis, B. R.; van Beek, H. F.; Rodríguez-Pacheco, J.; Lin, R. P.
2020A&A...642A..15K Altcode:
<BR /> Aims: The Spectrometer Telescope for Imaging X-rays (STIX)
on Solar Orbiter is a hard X-ray imaging spectrometer, which
covers the energy range from 4 to 150 keV. STIX observes hard X-ray
bremsstrahlung emissions from solar flares and therefore provides
diagnostics of the hottest (⪆10 MK) flare plasma while quantifying
the location, spectrum, and energy content of flare-accelerated
nonthermal electrons. <BR /> Methods: To accomplish this, STIX applies
an indirect bigrid Fourier imaging technique using a set of tungsten
grids (at pitches from 0.038 to 1 mm) in front of 32 coarsely pixelated
CdTe detectors to provide information on angular scales from 7 to 180
arcsec with 1 keV energy resolution (at 6 keV). The imaging concept of
STIX has intrinsically low telemetry and it is therefore well-suited
to the limited resources available to the Solar Orbiter payload. To
further reduce the downlinked data volume, STIX data are binned on
board into 32 selectable energy bins and dynamically-adjusted time
bins with a typical duration of 1 s during flares. <BR /> Results:
Through hard X-ray diagnostics, STIX provides critical information
for understanding the acceleration of electrons at the Sun and their
transport into interplanetary space and for determining the magnetic
connection of Solar Orbiter back to the Sun. In this way, STIX serves
to link Solar Orbiter's remote and in-situ measurements.
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Title: Exploiting Solar Visible-Range Observations by Inversion
Techniques: From Flows in the Solar Subsurface to a Flaring Atmosphere
Authors: Švanda, Michal; Jurčák, Jan; Korda, David; Kašparová,
Jana
2020rfma.book..349S Altcode:
Observations of the Sun in the visible spectral range belong to standard
measurements obtained by instruments both on the ground and in the
space. Nowadays, both nearly continuous full-disc observations with
medium resolution and dedicated campaigns of high spatial, spectral
and/or temporal resolution constitute a holy grail for studies that
can capture (both) the long- and short-term changes in the dynamics
and energetics of the solar atmosphere. Observations of photospheric
spectral lines allow us to estimate not only the intensity at small
regions, but also various derived data products, such as the Doppler
velocity and/or the components of the magnetic field vector. We show
that these measurements contain not only direct information about the
dynamics of solar plasmas at the surface of the Sun but also imprints
of regions below and above it. Here, we discuss two examples: First,
the local time-distance helioseismology as a tool for plasma dynamic
diagnostics in the near subsurface and second, the determination of
the solar atmosphere structure during flares. The methodology in both
cases involves the technique of inverse modelling.
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Title: Drifting Pulsation Structure at the Very Beginning of the
2017 September 10 Limb Flare
Authors: Karlický, Marian; Chen, Bin; Gary, Dale E.; Kašparová,
Jana; Rybák, Jan
2020ApJ...889...72K Altcode: 2019arXiv191212518K
Drifting pulsation structures (DPSs) are important radio fine structures
usually observed at the beginning of eruptive solar flares. It has been
suggested that DPSs carry important information on the energy release
processes in solar flares. We study DPS observed in an X8.2-class flare
on 2017 September 10 in the context of spatial and spectral diagnostics
provided by microwave, EUV, and X-ray observations. We describe DPS
and its substructures that were observed for the first time. We use a
new wavelet technique to reveal characteristic periods in DPS and their
frequency bands. Comparing the periods of pulsations found in this DPS
with those in previous DPSs, we found new very short periods in the
0.09-0.15 s range. We present Expanded Owens Valley Solar Array images
and spectra of microwave sources observed during the DPS. This DPS at
its very beginning has pulsations in two frequency bands (1000-1300 MHz
and 1600-1800 MHz), which are interconnected by fast drifting bursts. We
show that these double-band pulsations started just at the moment when
the ejected filament splits apart in a tearing motion at the location
where a signature of the flare current sheet later appeared. Using the
standard flare model and previous observations of DPSs, we interpret
these double-band pulsations as a radio signature of superthermal
electrons trapped in the rising magnetic rope and flare arcade at the
moment when the flare magnetic reconnection starts. The results are
discussed in a scenario with the plasmoid in the rising magnetic rope.
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Title: Exploiting solar visible-range observations by inversion
techniques: from flows in the solar subsurface to a flaring atmosphere
Authors: Švanda, Michal; Jurčák, Jan; Korda, David; Kašparová,
Jana
2020arXiv200103874S Altcode:
Observations of the Sun in the visible spectral range belong to standard
measurements obtained by instruments both on the ground and in the
space. Nowadays, both nearly continuous full-disc observations with
medium resolution and dedicated campaigns of high spatial, spectral
and/or temporal resolution constitute a holy grail for studies that
can capture (both) the long- and short-term changes in the dynamics
and energetics of the solar atmosphere. Observations of photospheric
spectral lines allow us to estimate not only the intensity at small
regions, but also various derived data products, such as the Doppler
velocity and/or the components of the magnetic field vector. We show
that these measurements contain not only direct information about the
dynamics of solar plasmas at the surface of the Sun but also imprints
of regions below and above it. Here, we discuss two examples: First,
the local time-distance helioseismology as a tool for plasma dynamic
diagnostics in the near subsurface and second, the determination of
the solar atmosphere structure during flares. The methodology in both
cases involves the technique of inverse modelling.
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Title: Radio, EUV, and X-Ray Observations during a Filament Rise in
the 2011 June 7 Solar Flare
Authors: Karlický, Marian; Kašparová, Jana; Sych, Robert
2020ApJ...888...18K Altcode: 2020arXiv200400122K
The most energetic flares start with a filament rise followed by
magnetic reconnection below this filament. The start of the reconnection
corresponds to the beginning of the flare impulsive phase. In this
paper we study processes before this phase. During the filament rise
we recognize an unusual radio continuum with a starting boundary
drifting toward lower frequencies. The estimated velocity of the agent
generating this continuum boundary is about 400 km s<SUP>-1</SUP>,
similar to that of the rising filament. In association with this
filament rise, transient X-ray sources and extreme ultraviolet (EUV)
brightenings are found near the filament footpoint and outside the
locations where later two parallel flare ribbons appear. Moreover,
oscillations with a ∼30 s period are found simultaneously in radio,
EUV, and X-ray observations. Around the end of these oscillations the
flare impulsive phase starts as seen in observations of the drifting
pulsation structure and X-ray source located at the upper part of the
rising filament. We interpret the unusual radio continuum and transient
X-ray sources, which are located outside the two parallel flare ribbons,
as those generated during an interaction of the rising filament with
the above-lying magnetic loops. The EUV brightening at the filament
footpoint could be a signature of the magnetic reconnection inside the
magnetic rope carrying the filament. Possible scenarios of the ∼30
s period oscillations in radio, X-ray, and EUV are discussed.
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Title: Modelling of Flare Processes: A Comparison of the Two RHD
Codes FLARIX and RADYN
Authors: Kašparová, Jana; Carlsson, Mats; Heinzel, Petr; Varady,
Michal
2019ASPC..519..141K Altcode:
We present a comparison of two autonomous, methodologically different
radiation hydrodynamic codes, FLARIX and RADYN, and their use to model
the solar flare processes. Both codes can model the time evolution
of a 1D atmosphere heated by a specified process, e.g. by electron
beams propagating from the injection site in the corona down to the
lower atmosphere. In such a scenario time scales can be rather short
and lead to fast heating on even sub-second time scales. Our aim is
to compare the FLARIX and RADYN codes using exactly the same setup
and model conditions. Although such a comparison has never been done
successfully before for this type of codes, we will present a close
agreement between the time evolution of the modelled atmospheric
structure for a test case of electron beam heating.
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Title: Heating of the solar photosphere during a white-light flare
Authors: Jurčák, Jan; Kašparová, Jana; Švanda, Michal; Kleint,
Lucia
2018A&A...620A.183J Altcode: 2018arXiv181107794J
Context. The Fe I lines observed by the Hinode/SOT spectropolarimeter
were always seen in absorption, apart from the extreme solar limb. Here
we analyse a unique dataset capturing these lines in emission during
a solar white-light flare. <BR /> Aims: We analyse the temperature
stratification in the solar photosphere during a white-light flare and
compare it with the post-white-light flare state. <BR /> Methods: We
used two scans of the Hinode/SOT spectropolarimeter to infer, by means
of the LTE inversion code Stokes Inversion based on Response function
(SIR), the physical properties in the solar photosphere during and
after a white-light flare. The resulting model atmospheres are compared
and the changes are related to the white-light flare. <BR /> Results:
We show that the analysed white-light flare continuum brightening is
probably not caused by the temperature increase at the formation height
of the photospheric continuum. However, the photosphere is heated
by the flare approximately down to log τ = -0.5 and this results
in emission profiles of the observed Fe I lines. From the comparison
with the post-white-light flare state of the atmosphere, we estimate
that the major contribution to the increase in the continuum intensity
originates in the heated chromosphere.
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Title: Fast velocities of flare ribbon kernels and ribbon elongation
in a quescent filament eruption of 2012 August 31 observed by SDO/AIA
Authors: Lörinčík, Juraj; Dudík, Jaroslav; Kašparová, Jana;
Aulanier, Guillaume; Zemanová, Alena; Dzifčáková, Elena
2018csc..confE..63L Altcode:
We report on SDO observations of an eruption of a quiescent filament
from 2012 August 31. In the 1600 Å filter channel of AIA, flare
ribbons were observed to elongate at velocities up to 480 km s^{-1}
and flare kernels move along a ribbon at velocity of ≈ 260 km
s^{-1}. In order to investigate the emission observed in the 1600 Å
channel, we used synthetic spectra modeled using CHIANTI and RADYN
models of flare atmospheres with beam parameters constrained using
fits of RHESSI spectra. We found out that depending on parameters of
heating of a flare model, thickness of a region where the emission
of the 1600 Å filter channel originates ranges between 10^{-2} and
10^{2} km. Information on dimensions of the formation region were
then utilized to estimate densities in flare ribbons using inversions
of the emission measure. These were found to range between 10^{10} -
4.10^{12} cm^{-3} for flare atmospheres heated by beams of different
parameters. Together with B_{LOS} data from SDO/HMI, diagnosed densities
were used to calculate Alfvén velocities in observed ribbons. These
can be as small as 17 km s^{-1} for flare ribbons observed in region of
weak magnetic field at latter stages of heating. This finding suggests
that elongation of ribbons and motion of kernels might not be related
to waves. Motions along the PIL are well-described in the 3D model of
solar eruptions of Aulanier et al. 2013 (A&A, 543, 110). However,
EUV observations of flare loops revealed that velocity of their apparent
slipping motion is much lower than velocity of elongation of a ribbon,
which is observed in a close vicinity. Therefore, observed phenomena can
not be directly related to super-Alvénic regime of magnetic slipping
reconnection introduced in the 3D model.
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Title: Broad Non-Gaussian Fe XXIV Line Profiles in the Impulsive
Phase of the 2017 September 10 X8.3-class Flare Observed by Hinode/EIS
Authors: Polito, Vanessa; Dudík, Jaroslav; Kašparová, Jana;
Dzifčáková, Elena; Reeves, Katharine K.; Testa, Paola; Chen, Bin
2018ApJ...864...63P Altcode: 2018arXiv180709361P
We analyze the spectra of high-temperature Fe XXIV lines observed by
the Hinode/Extreme-Ultraviolet Imaging Spectrometer (EIS) during the
impulsive phase of the X8.3-class flare on 2017 September 10. The
line profiles are broad, show pronounced wings, and clearly depart
from a single-Gaussian shape. The lines can be well fitted with κ
distributions, with values of κ varying between ≈1.7 and 3. The
regions where we observe the non-Gaussian profiles coincide with
the location of high-energy (≈100-300 keV) hard X-ray (HXR) sources
observed by RHESSI, suggesting the presence of particle acceleration or
turbulence, also confirmed by the observations of nonthermal microwave
sources with the Expanded Owens Valley Solar Array at and above the HXR
loop-top source. We also investigate the effect of taking into account
κ distributions in the temperature diagnostics based on the ratio of
the Fe XXIII λ263.76 and Fe XXIV λ255.1 EIS lines. We found that
these lines can be formed at much higher temperatures than expected
(up to log(T[K]) ≈ 7.8) if departures from Maxwellian distributions
are taken into account. Although larger line widths are expected because
of these higher formation temperatures, the observed line widths still
imply nonthermal broadening in excess of 200 km s<SUP>-1</SUP>. The
nonthermal broadening related to HXR emission is better interpreted
by turbulence than by chromospheric evaporation.
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Title: Broad Non-Gaussian fe XXIV Line Profiles in the Impulsive
Phase of the 2017 September 10 X8.3-CLASS Flare Observed by Hinode/eis
Authors: Polito, Vanessa; Dudik, Jaroslav; Kasparova, Jana; Dzifcakova,
Elena; Reeves, Katharine K.; Testa, Paola; Chen, Bin
2018shin.confE.212P Altcode:
We analyze the spectra of high temperature Fe XXIV lines observed by
Hinode/EIS during the impulsive phase the X8.3-class flare on September
10, 2017. The line profiles are broad, show pronounced wings, and
clearly depart from a single Gaussian shape. The lines can be well
fitted with the ? distributions, with values of ? varying between
?1.7 to 3. The region where we observe the non-Gaussian profiles
coincides with the location of high-energy (?100-300 keV) HXR sources
observed by RHESSI, suggesting the presence of particle acceleration
or turbulence, also confirmed by the observations of a non-thermal
microwave sources with EOVSA at and above the HXR looptop source. We
also investigate the effect of taking into account ? distributions in
the temperature diagnostics based on the ratio of the Fe XXIII 263.76
?A and Fe XXIV 255.1 ?A EIS lines. We found that these lines can be
formed at much higher temperatures than expected (up to log(T [K])
? 7.8), if departures from Maxwellian distributions are taken into
account. Although larger line widths are expected because of these
higher formation temperatures, the observed line widths still imply
non-thermal broadening in excess of 200kms?1.
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Title: Understanding the HMI Pseudocontinuum in White-light Solar
Flares
Authors: Švanda, Michal; Jurčák, Jan; Kašparová, Jana; Kleint,
Lucia
2018ApJ...860..144S Altcode: 2018arXiv180503369S
We analyze observations of the X9.3 solar flare (SOL2017-09-06T11:53)
observed by SDO/HMI and Hinode/Solar Optical Telescope. Our aim is to
learn about the nature of the HMI pseudocontinuum I <SUB>c</SUB> used as
a proxy for the white-light continuum. From model atmospheres retrieved
by an inversion code applied to the Stokes profiles observed by the
Hinode satellite, we synthesize profiles of the Fe I 617.3 nm line and
compare them to HMI observations. Based on a pixel-by-pixel comparison,
we show that the value of I <SUB>c</SUB> represents the continuum level
well in quiet-Sun regions only. In magnetized regions, it suffers from
a simplistic algorithm that is applied to a complex line shape. During
this flare, both instruments also registered emission profiles in the
flare ribbons. Such emission profiles are poorly represented by the
six spectral points of HMI and the MDI-like algorithm does not account
for emission profiles in general; thus, the derived pseudocontinuum
intensity does not approximate the continuum value properly.
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Title: On the Nature of Off-limb Flare Continuum Sources Detected
by SDO/HMI
Authors: Heinzel, P.; Kleint, L.; Kašparová, J.; Krucker, S.
2017ApJ...847...48H Altcode: 2017arXiv170906377H
The Helioseismic and Magnetic Imager on board the Solar Dynamics
Observatory has provided unique observations of off-limb flare
emission. White-light continuum enhancements were detected in the
“continuum” channel of the Fe 6173 Å line during the impulsive
phase of the observed flares. In this paper we aim to determine which
radiation mechanism is responsible for such enhancement being seen above
the limb, at chromospheric heights around or below 1000 km. Using a
simple analytical approach, we compare two candidate mechanisms, the
hydrogen recombination continuum (Paschen) and the Thomson continuum
due to scattering of disk radiation on flare electrons. Both mechanisms
depend on the electron density, which is typically enhanced during the
impulsive phase of a flare as the result of collisional ionization (both
thermal and also non-thermal due to electron beams). We conclude that
for electron densities higher than 10<SUP>12</SUP> cm<SUP>-3</SUP>,
the Paschen recombination continuum significantly dominates the
Thomson scattering continuum and there is some contribution from the
hydrogen free-free emission. This is further supported by detailed
radiation-hydrodynamical (RHD) simulations of the flare chromosphere
heated by the electron beams. We use the RHD code FLARIX to compute the
temporal evolution of the flare-heating in a semi-circular loop. The
synthesized continuum structure above the limb resembles the off-limb
flare structures detected by HMI, namely their height above the limb,
as well as the radiation intensity. These results are consistent with
recent findings related to hydrogen Balmer continuum enhancements,
which were clearly detected in disk flares by the IRIS near-ultraviolet
spectrometer.
---------------------------------------------------------
Title: Hybrid simulations of chromospheric HXR flare sources
Authors: Moravec, Z.; Varady, M.; Kašparová, J.; Kramoliš, D.
2016AN....337.1020M Altcode: 2016arXiv160107026M
Recent measurements of vertical extents and positions of the
chromospheric hard X-ray (HXR) flare sources based on Ramaty
High-Energy Spectroscopic Imager (RHESSI) observations show a
significant inconsistency with the theoretical predictions based on
the standard collisional thick target model (CTTM). Using the hybrid
flare code Flarix, we model simultaneously and self-consistently
the propagation, scattering and energy losses of electron beams with
power-law energy spectra and various initial pitch-angle distributions
in a purely collisional approximation and concurrently the dynamic
response of the heated chromosphere on timescales typical for RHESSI
image reconstruction. The results of the simulations are used to model
the time evolution of the vertical distribution of chromospheric HXR
source within a singular (compact) loop. Adopting the typical RHESSI
imaging times scales, energy dependent vertical sizes and positions
as could be observed by RHESSI are presented.
---------------------------------------------------------
Title: Numerical RHD simulations of flaring chromosphere with Flarix
Authors: Heinzel, Petr; Kašparová, Jana; Varady, Michal; Karlický,
Marian; Moravec, Zdeněk
2016IAUS..320..233H Altcode: 2016arXiv160200016H
Flarix is a radiation-hydrodynamical (RHD) code for modeling of the
response of the chromosphere to a beam bombardment during solar
flares. It solves the set of hydrodynamic conservation equations
coupled with NLTE equations of radiative transfer. The simulations are
driven by high energy electron beams. We present results of the Flarix
simulations of a flaring loop relevant to the problem of continuum
radiation during flares. In particular we focus on properties of the
hydrogen Balmer continuum which was recently detected by IRIS.
---------------------------------------------------------
Title: Mg II Lines Observed During the X-class Flare on 29 March
2014 by the Interface Region Imaging Spectrograph
Authors: Liu, W.; Heinzel, P.; Kleint, L.; Kašparová, J.
2015SoPh..290.3525L Altcode: 2015SoPh..tmp..166L; 2015arXiv151100480L
Mg II lines represent one of the strongest emissions from the
chromospheric plasma during solar flares. In this article, we
studied the Mg II lines observed during the X1 flare on 29 March 2014
(SOL2014-03-29T17:48) by the Interface Region Imaging Spectrograph
(IRIS). IRIS detected large intensity enhancements of the Mg II h and
k lines, subordinate triplet lines, and several other metallic lines
at the flare footpoints during this flare. We have used the advantage
of the slit-scanning mode (rastering) of IRIS and performed, for the
first time, a detailed analysis of spatial and temporal variations
of the spectra. Moreover, we were also able to identify positions
of strongest hard X-ray (HXR) emissions using the Reuven Ramaty
High Energy Solar Spectroscopic Imager (RHESSI) observations and to
correlate them with the spatial and temporal evolution of IRIS Mg
II spectra. The light curves of the Mg II lines increase and peak
contemporarily with the HXR emissions but decay more gradually. There
are large red asymmetries in the Mg IIh and k lines after the flare
peak. We see two spatially well-separated groups of Mg II line profiles,
non-reversed and reversed. In some cases, the Mg II footpoints with
reversed profiles are correlated with HXR sources. We show the spatial
and temporal behavior of several other line parameters (line metrics)
and briefly discuss them. Finally, we have synthesized the Mg IIk line
using our non-LTE code with the Multilevel Accelerated Lambda Iteration
(MALI) technique. Two kinds of models are considered, the flare model
F2 of Machado et al. (Astrophys. J.242, 336, 1980) and the models of
Ricchiazzi and Canfield (Astrophys. J.272, 739, 1983, RC models). Model
F2 reproduces the peak intensity of the non-reversed Mg IIk profile
at flare maximum, but does not account for high wing intensities. On
the other hand, the RC models show the sensitivity of Mg II line
intensities to various electron-beam parameters. Our simulations also
show that the microturbulence produces a broader line core, while the
intense line wings are caused by an enhanced line source function.
---------------------------------------------------------
Title: Numerical simulations of flaring loops with Flarix
Authors: none Heinzel, Petr; Karlicky, Marian; Varady, Michal;
Kasparova, Jana; Moravec, Zdenek
2015IAUGA..2258466N Altcode:
Flarix is the radiation-hydrodynamical code for simulation of the
flare evolution. It solves the set of hydrodynamicval equations
coupled to NLTE equations of radiative transfer. The simulation is
driven by the accelerated electron beams. We present new results of
Flarix simulations for various types of flare loops, incorporating new
features like effects of the return current and particle re-acceleration
in the chromosphere.
---------------------------------------------------------
Title: IRIS observations of MgII lines in solar flares
Authors: none Heinzel, Petr; Liu, Wenjuan; Kleint, Lucia; Kasparova,
Jana
2015IAUGA..2258503N Altcode:
We present the results of first analysis of IRIS NUV spectra in an
X-class flare of29 March 2014.
---------------------------------------------------------
Title: Modifications of thick-target model: re-acceleration of
electron beams by static and stochastic electric fields
Authors: Varady, M.; Karlický, M.; Moravec, Z.; Kašparová, J.
2014A&A...563A..51V Altcode: 2014arXiv1401.3329V
Context. The collisional thick-target model (CTTM) of the impulsive
phase of solar flares, together with the famous Carmichael, Sturrock,
Hirayama, and Kopp-Pneuman (CSHKP) model, presented for many years a
"standard" model, which straightforwardly explained many observational
aspects of flares. On the other hand, many critical issues appear when
the concept is scrutinised theoretically or with the new generation of
hard X-ray (HXR) observations. The famous "electron number problem"
or problems related to transport of enormous particle fluxes though
the corona represent only two of them. To resolve the discrepancies,
several modifications of the CTTM appeared. <BR /> Aims: We study two
of them based on the global and local re-acceleration of non-thermal
electrons by static and stochastic electric fields during their
transport from the coronal acceleration site to the thick-target
region in the chromosphere. We concentrate on a comparison of the
non-thermal electron distribution functions, chromospheric energy
deposits, and HXR spectra obtained for both considered modifications
with the CTTM itself. <BR /> Methods: The results were obtained using
a relativistic test-particle approach. We simulated the transport
of non-thermal electrons with a power-law spectrum including the
influence of scattering, energy losses, magnetic mirroring, and also
the effects of the electric fields corresponding to both modifications
of the CTTM. <BR /> Results: We show that both modifications of the
CTTM change the outcome of the chromospheric bombardment in several
aspects. The modifications lead to an increase in chromospheric energy
deposit, change of its spatial distribution, and a substantial increase
in the corresponding HXR spectrum intensity. <BR /> Conclusions: The
re-acceleration in both models reduces the demands on the efficiency
of the primary coronal accelerator, on the electron fluxes transported
from the corona downwards, and on the total number of accelerated
coronal electrons during flares.
---------------------------------------------------------
Title: MgII lines in solar flares: IRIS observations and NLTE modeling
Authors: Heinzel, Petr; Kasparova, Jana; Kleint, Lucia; Dzifcakova,
Elena
2014cosp...40E1182H Altcode:
Chromospheric flares have been recently observed in MgII resonance
lines by the IRIS instrument. Apart from the resonance lines h and k,
also subordinate line emissions due to transitions between the MgII
levels 3P and 3D have been now detected by IRIS during flares. We apply
the NLTE radiative-transfer code to synthesize all these MgII lines
under typical flare conditions. In particular, we focus on the role
of the non-thermal excitations and ionizations, which are due to the
presence of the electron beams and corresponding return currents. The
results of this modeling are compared with new IRIS data.
---------------------------------------------------------
Title: A new approach to model particle acceleration and energy
transfer in solar flares
Authors: Rubio Da Costa, Fatima; Zuccarello, F.; Fletcher, L.;
Labrosse, N.; Kasparova, J.; Prosecký, T.; Carlsson, M.; Petrosian,
V.; Liu, W.
2013SPD....4440401R Altcode:
Motivated by available observations of two different flares in Lyα and
Hα, we model the conditions of the solar atmosphere using a radiation
hydrodynamics code (RADYN, Carlsson & Stein, 1992) and analyze the
energy transport carried by a beam of non-thermal electrons injected
at the top of a 1D coronal loop. The numerical Lyα and Hα intensities
match with the observations. The electron energy distribution is assumed
to follow a power law of the form (E/E<SUP>c</SUP> )<SUB>-δ</SUB> for
energies greater than a cutoff value of E<SUP>c</SUP>. Abbett &
Hawley (1999) and Allred et al. (2005) assumed that the non-thermal
electrons flux injected at the top of a flaring loop, the cut-off energy
and the power law index are constant over time. An improvement was
achieved by Allred & Hawley (2006), who modified the RADYN code
in such a way that the input parameters were time dependent. Their
inputs were based on observations of a flare obtained with RHESSI. By
combining RADYN with the “flare” code from Stanford University
which models the acceleration and transport of particles and radiation
of solar flares in non-LTE regime, we can calculate the non-thermal
electrons flux, the cut-off energy and the power law index at every
simulated time step. The atmospheric parameters calculated by RADYN
could in turn be used as updated inputs for "flare", providing several
advantages over the results from Liu et al. (2009), who combined the
particle acceleration code with a 1-D hydrodynamic code, improving
the atmospheric conditions.
---------------------------------------------------------
Title: Observational consequences of the local re-acceleration
thick-target model
Authors: Varady, M.; Moravec, Z.; Karlický, M.; Kašparová, J.
2013JPhCS.440a2013V Altcode:
In our contribution we compare the efficiency of the hard X-ray
production and the vertical sizes and positions of the hard X-ray
sources for the classical collisional thick-target model and for its
recently proposed modification, the local re-acceleration thick-target
model. The latter model has been proposed in order to ease some
of the severe theoretical problems of the collisional thick-target
model related to interpretation of the observational properties of the
foot-point HXR sources in solar flares. The results are obtained using
a relativistic test-particle approach for a fully ionised atmosphere
with a converging magnetic field and a single (compact) flare loop.
---------------------------------------------------------
Title: Solar flares at submillimeter wavelengths
Authors: Krucker, Säm; Giménez de Castro, C. G.; Hudson, H. S.;
Trottet, G.; Bastian, T. S.; Hales, A. S.; Kašparová, J.; Klein,
K. -L.; Kretzschmar, M.; Lüthi, T.; Mackinnon, A.; Pohjolainen, S.;
White, S. M.
2013A&ARv..21...58K Altcode:
We discuss the implications of the first systematic observations of
solar flares at submillimeter wavelengths, defined here as observing
wavelengths shorter than 3 mm (frequencies higher than 0.1 THz). The
events observed thus far show that this wave band requires a new
understanding of high-energy processes in solar flares. Several events,
including observations from two different observatories, show during
the impulsive phase of the flare a spectral component with a positive
(increasing) slope at the highest observable frequencies (up to 405
GHz). To emphasize the increasing spectra and the possibility that
these events could be even more prominent in the THz range, we term
this spectral feature a "THz component". Here we review the data and
methods, and critically assess the observational evidence for such
distinct component(s). This evidence is convincing. We also review the
several proposed explanations for these feature(s), which have been
reported in three distinct flare phases. These data contain important
clues to flare development and particle acceleration as a whole, but
many of the theoretical issues remain open. We generally have lacked
systematic observations in the millimeter-wave to far-infrared range
that are needed to complete our picture of these events, and encourage
observations with new facilities.
---------------------------------------------------------
Title: Simulations of HXR Foot-point Source Sizes for Modified
Thick-target Models
Authors: Moravec, Z.; Varady, M.; Karlický, M.; Kašparová, J.
2013CEAB...37..535M Altcode:
We study vertical sizes of foot-point hard X-ray (HXR) sources using a
relativistic test particle approach in a flare loop with a converging
magnetic field. We compare results for the Collisional Thick Target
Model (CTTM) with recently proposed modifications of the CTTM comprising
a secondary acceleration of beam electrons. Our preliminary results
indicate that none of the proposed modifications of the CTTM can explain
the observed sizes of the HXR sources in a single loop flare scenario.
---------------------------------------------------------
Title: The spectrometer telescope for imaging x-rays on board the
Solar Orbiter mission
Authors: Benz, A. O.; Krucker, S.; Hurford, G. J.; Arnold, N. G.;
Orleanski, P.; Gröbelbauer, H. -P.; Klober, S.; Iseli, L.; Wiehl,
H. J.; Csillaghy, A.; Etesi, L.; Hochmuth, N.; Battaglia, M.;
Bednarzik, M.; Resanovic, R.; Grimm, O.; Viertel, G.; Commichau, V.;
Meuris, A.; Limousin, O.; Brun, S.; Vilmer, N.; Skup, K. R.; Graczyk,
R.; Stolarski, M.; Michalska, M.; Nowosielski, W.; Cichocki, A.;
Mosdorf, M.; Seweryn, K.; Przepiórka, A.; Sylwester, J.; Kowalinski,
M.; Mrozek, T.; Podgorski, P.; Mann, G.; Aurass, H.; Popow, E.;
Onel, H.; Dionies, F.; Bauer, S.; Rendtel, J.; Warmuth, A.; Woche,
M.; Plüschke, D.; Bittner, W.; Paschke, J.; Wolker, D.; Van Beek,
H. F.; Farnik, F.; Kasparova, J.; Veronig, A. M.; Kienreich, I. W.;
Gallagher, P. T.; Bloomfield, D. S.; Piana, M.; Massone, A. M.;
Dennis, B. R.; Schwarz, R. A.; Lin, R. P.
2012SPIE.8443E..3LB Altcode:
The Spectrometer Telescope for Imaging X-rays (STIX) is one of 10
instruments on board Solar Orbiter, a confirmed Mclass mission of the
European Space Agency (ESA) within the Cosmic Vision program scheduled
to be launched in 2017. STIX applies a Fourier-imaging technique
using a set of tungsten grids (at pitches from 0.038 to 1 mm) in
front of 32 pixelized CdTe detectors to provide imaging spectroscopy
of solar thermal and non-thermal hard X-ray emissions from 4 to 150
keV. The status of the instrument reviewed in this paper is based on
the design that passed the Preliminary Design Review (PDR) in early
2012. Particular emphasis is given to the first light of the detector
system called Caliste-SO.
---------------------------------------------------------
Title: Formation of Balmer Lines in Impulsively Heated Flare
Atmosphere by Neutral Beams
Authors: Varady, M.; Kašparová, J.; Moravec, Z.; Karlický, M.;
Heinzel, P.
2012ASPC..454..341V Altcode:
In the context of interpreting non-thermal hard X-ray emission and γ
lines emanating from the footpoints of flare loops, most contemporary
flare models assign a fundamental role during the flare energy release,
transport and deposition to the high energy non-thermal particle
beams. In this contribution we concentrate on modelling of the
spectroscopic properties of chromospheric flare emission in optical
hydrogen lines generated due to the bombardment of the chromosphere
and photosphere by neutral beams with power-law spectra. In order
to obtain an estimate of the neutral beam flare heating in the solar
atmosphere we produced a simple model describing the propagation and
thermalisation of neutral beams. We compare the neutral beam flare
heating with the flare heating produced by corresponding pure electron
and proton beams. Further we compare the contribution functions for
Hα line obtained for neutral and electron beam heating.
---------------------------------------------------------
Title: Diagnostics of Non-Thermal Distribution from RESIK and RHESSI
Flare Spectra
Authors: Kulinová, A.; Kašparová, J.; Dzifčáková, E.; Sylwester,
J.; Sylwester, B.
2012ASPC..454..329K Altcode:
Solar flare spectra observed by the X-ray spectrometers RESIK and
RHESSI with high energy resolution enabled us to analyse possible
non-thermality of plasma electron distribution in the keV range. For
RESIK diagnostics (in the 2-4 keV range) we assumed that the bulk
of the plasma is represented by the so-called n-distribution, which
describes the deviations from the Maxwellian distribution by two
parameters: n and T. Using thick-target approximation for RHESSI
spectral analysis, we obtained characteristics of injected electron
power-law distribution in the deka-keV range. The event presented here
shows a very good time correlation of non-thermality obtained from
the RESIK spectra with appearance of non-thermal component in RHESSI
and/or radio spectra. However, a thermal component was still present
in RHESSI. Both spectral and imaging information in RHESSI soft and
hard X-ray ranges were used for the estimation of the ratio of thermal
to non-thermal electron densities of the X-ray emitting plasma.
---------------------------------------------------------
Title: Influence of Static and Stochastic Electric Fields on Electron
Beams Bombarding the Chromosphere
Authors: Varady, M.; Karlický, M.; Moravec, Z.; Kašparová, J.
2012ASPC..456..203V Altcode:
Using a relativistic test-particle code we study and compare the
influence of static and stochastic electric fields on propagation
of electron beams along the magnetic fieldlines through the solar
atmosphere given by the VAL C model from the primary acceleration site
in the corona downwards to the chromosphere. The results are compared
with the most common, classical model of electron beam propagation,
scattering and thermalisation given by Emslie (1978). The effects
of the fields on the chromospheric heating and hard X-ray emission
are discussed.
---------------------------------------------------------
Title: The non-Maxwellian continuum in the X-ray, UV, and radio range
Authors: Dudík, J.; Kašparová, J.; Dzifčáková, E.; Karlický,
M.; Mackovjak, Š.
2012A&A...539A.107D Altcode:
<BR /> Aims: We investigate the X-ray, UV, and also the radio
continuum arising from plasmas with a non-Maxwellian distribution of
electron energies. The two investigated types of distributions are
the κ- and n-distributions. <BR /> Methods: We derived analytical
expressions for the non-Maxwellian bremsstrahlung and free-bound
continuum spectra. The spectra were calculated using available
cross-sections. Then we compared the bremsstrahlung spectra arising from
the different bremsstrahlung cross-sections that are routinely used
in solar physics. <BR /> Results: The behavior of the bremsstrahlung
spectra for the non-Maxwellian distributions is highly dependent
on the assumed type of the distribution. At flare temperatures and
hard X-ray energies, the bremsstrahlung is greatly increased for
κ-distributions and exhibits a strong high-energy tail. With decreasing
κ, the maximum of the bremsstrahlung spectrum decreases and moves
to higher wavelengths. In contrast, the maximum of the spectra for
n-distributions increases with increasing n, and the spectrum then
falls off very steeply with decreasing wavelength. In the millimeter
radio range, the non-Maxwellian bremsstrahlung spectra are almost
parallel to the thermal bremsstrahlung. Therefore, the non-Maxwellian
distributions cannot be detected by off-limb observations made by the
ALMA instrument. The free-bound continua are also highly dependent
on the assumed type of the distribution. For n-distributions, the
ionization edges disappear and a smooth continuum spectrum is formed
for n ≧ 5. Opposite behavior occurs for κ-distributions where
the ionization edges are in general significantly enhanced, with
details depending on κ and T through the ionization equilibrium. We
investigated how the non-Maxwellian κ-distributions can be
determined from the observations of the continuum and conclude that
one can sample the low-energy part of the distribution from the
continuum. <P />Appendix A is available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Solar flares in Halpha and Ly-alpha : observations vs
simulations.
Authors: Rubio da Costa, F.; Zuccarello, F.; Fletcher, L.; Labrosse,
N.; Prosecký, T.; Kašparová, J.
2012MSAIS..19..117R Altcode:
In order to study the properties of faint, moderate and bright flares,
we simulate the conditions of the solar atmosphere using a radiative
hydrodynamic model \citep{2005ApJ...630..573A}. A constant beam of
non-thermal electrons is injected at the apex of a 1D coronal loop
and heating from thermal soft X-ray and UV emission is included. We
study the contribution of different processes to the total intensity of
different lines at different atmospheric layers. We obtain the total
integrated intensity of different lines and we compare those of the
Ly-alpha and Halpha lines with the observational values for Ly-alpha
(using TRACE 1216 and 1600 Å data and estimating the “pure” Ly-alpha
emission) and Halpha (using data from the Ondřejov Observatory). We
inferred from the analysis of the values obtained by simulation that
the X-ray energy of the different kind of flares does not strongly
affect the Ly-alpha results; the Halpha results are comparable to the
observed ones, concluding that the simulated solar atmosphere fits
better at lower layers of the chromosphere than at upper layers.
---------------------------------------------------------
Title: The Diagnostics of the Shape of the Electron Distribution
Function during the Solar Flares
Authors: Dzifčáková, E.; Kulinová, A.; Kašparová, J.
2011ASPC..448.1095D Altcode: 2011csss...16.1095D
The non-thermal electrons accelerated during the flares interact with
surrounding plasma and the electron distribution of the flaring plasma
becomes non-Maxwellian. X-ray spectrometers RESIK and RHESSI with
high energy resolution give an opportunity to diagnose the presence
of the non-thermal electron distribution. RESIK X-line spectra with
high fluxes of satellite lines can be explained by presence of the
non-thermal n-distribution in a plasma bulk in the 2-2.5 keV range. The
RHESSI spectrometer enables us to diagnose the non-thermal high-energy
tail of the electron distribution in deka-keV energy range. This
high-energy tail can be described by a power-law distribution. We
have analyzed three solar flares to get non-thermal characteristics
of both non-thermal parts of the electron distribution. The ratios
of the intensities of allowed to satellite lines have been used to
estimate the parameters of the n-distribution. RHESSI data has been
used to obtain the temporal changes of the parameters of Maxwellian and
power-law distributions and also for determination of the parameters of
n-distribution in two specific cases. The parameters of n-distribution
obtained from RHESSI analysis agree within the errors with those derived
from RESIK observations. Finally, the synthetic soft X-ray line spectra
has been computed for diagnosed parameters of distributions and have
been compared with RESIK X-ray observations.
---------------------------------------------------------
Title: Diagnostics of non-thermal distributions in solar flare
spectra observed by RESIK and RHESSI
Authors: Kulinová, A.; Kašparová, J.; Dzifčáková, E.; Sylwester,
J.; Sylwester, B.; Karlický, M.
2011A&A...533A..81K Altcode: 2011arXiv1109.1011K
Context. During solar flares an enormous amount of energy is released,
and the charged particles, like electrons, are accelerated. These
non-thermal electrons interact with the plasma in various parts
of solar flares, where the distribution function of electrons can
therefore be non-Maxwellian. <BR /> Aims: We focus on the non-thermal
components of the electron distribution in the keV range and analyse
high-energy resolution X-ray spectra detected by RESIK and RHESSI for
three solar flares. <BR /> Methods: In the 2-4 keV range we assume that
the electron distribution can be modelled by an n-distribution. Using
a method of line-intensity ratios, we analyse allowed and satellite
lines of Si observed by RESIK and estimate the parameters of this
n-distribution. At higher energies we explore RHESSI bremsstrahlung
spectra. Adopting a forward-fitting approach and thick-target
approximation, we determine the characteristics of injected electron
beams. <BR /> Results: RHESSI non-thermal component associated with
the electron beam is correlated well with presence of the non-thermal
n-distribution obtained from the RESIK spectra. In addition, such an
n-distribution occurs during radio bursts observed in the 0.61-15.4
GHz range. Furthermore, we show that the n-distribution could also
explain RHESSI emission below ~5 keV. Therefore, two independent
diagnostics methods indicate the flare plasma being affected by
the electron beam can have a non-thermal component in the ~2-5 keV
range, which is described by the n-distribution well. Finally,
spectral line analysis reveals that the n-distribution does not
occupy the same location as the thermal component detected by RHESSI
at ~10 keV. <P />Appendix A is available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
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.
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: Deducing Electron Properties from Hard X-ray Observations
Authors: Kontar, E. P.; Brown, J. C.; Emslie, A. G.; Hajdas, W.;
Holman, G. D.; Hurford, G. J.; Kašparová, J.; Mallik, P. C. V.;
Massone, A. M.; McConnell, M. L.; Piana, M.; Prato, M.; Schmahl,
E. J.; Suarez-Garcia, E.
2011SSRv..159..301K Altcode: 2011arXiv1110.1755K; 2011SSRv..tmp..279K
X-radiation from energetic electrons is the prime diagnostic of
flare-accelerated electrons. The observed X-ray flux (and polarization
state) is fundamentally a convolution of the cross-section for the hard
X-ray emission process(es) in question with the electron distribution
function, which is in turn a function of energy, direction, spatial
location and time. To address the problems of particle propagation
and acceleration one needs to infer as much information as possible on
this electron distribution function, through a deconvolution of this
fundamental relationship. This review presents recent progress toward
this goal using spectroscopic, imaging and polarization measurements,
primarily from the Reuven Ramaty High Energy Solar Spectroscopic
Imager ( RHESSI). Previous conclusions regarding the energy, angular
(pitch angle) and spatial distributions of energetic electrons in
solar flares are critically reviewed. We discuss the role and the
observational evidence of several radiation processes: free-free
electron-ion, free-free electron-electron, free-bound electron-ion,
photoelectric absorption and Compton backscatter (albedo), using both
spectroscopic and imaging techniques. This unprecedented quality of
data allows for the first time inference of the angular distributions
of the X-ray-emitting electrons and improved model-independent
inference of electron energy spectra and emission measures of
thermal plasma. Moreover, imaging spectroscopy has revealed hitherto
unknown details of solar flare morphology and detailed spectroscopy of
coronal, footpoint and extended sources in flaring regions. Additional
attempts to measure hard X-ray polarization were not sufficient to put
constraints on the degree of anisotropy of electrons, but point to the
importance of obtaining good quality polarization data in the future.
---------------------------------------------------------
Title: Solar flares: observations vs simulations
Authors: Rubio da Costa, Fatima; Zuccarello, Francesca; Labrosse,
Nicolas; Fletcher, Lyndsay; Prosecký, Tomáš; Kašparová, Jana
2011IAUS..274..182R Altcode:
In order to study the properties of faint, moderate and bright flares,
we simulate the conditions of the solar atmosphere using a radiative
hydrodynamic model (Abbett & Hawley, 1999). A constant beam of
non-thermal electrons is injected at the apex of a 1D coronal loop and
heating from thermal soft X-ray emission is included. We compare the
results with some observational data in Ly-α (using TRACE 1216 and
1600 Å data and estimating the “pure” Ly-α emission) and in Hα
(data taken with a Multichannel Flare Spectrograph, at the Ondrejov
Observatory).
---------------------------------------------------------
Title: Diagnostics of non-thermal distribution from solar flares
spectra - RESIK
Authors: Kulinová, A.; Kašparová, J.; Dzifčáková, E.
2010nspm.conf...77K Altcode:
Solar flares spectra observed by X-ray spectrometers RESIK and RHESSI
made possible detecting and diagnosing non-thermal effects in the
flare plasma in energy range from 2 keV to several tens of keV. Based
on previous studies we have assumed that the core of a non-thermal
distribution behaves like a so-called n-distribution mixed with
a thermal component, and its high-energy tail can be described by
a power-law relation. We used two different diagnostics: spectral
lines ratia (RESIK) and a raw target model with a thermal component
(RHESSI) to obtain parameters of these parts of the free electron
'model' distribution.
---------------------------------------------------------
Title: Modeling of Solar Flare Plasma and Its Radiation
Authors: Varady, Michal; Kasparova, Jana; Moravec, Zdeněk; Heinzel,
Petr; Karlicky, Marian
2010ITPS...38.2249V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electron beam - plasma system with the return current and
directivity of its X-ray emission
Authors: Karlický, M.; Kašparová, J.
2009A&A...506.1437K Altcode: 2009arXiv0909.0146K
Aims: An evolution of the electron distribution function in the
beam-plasma system with the return current is computed numerically for
different parameters. The X-ray bremsstrahlung corresponding to such an
electron distribution is calculated and the directivity of the X-ray
emission is studied. <BR />Methods: For computations of the electron
distribution functions we used a 3-D particle-in-cell electromagnetic
code. The directivity of the X-ray emission was calculated using
the angle-dependent electron-ion bremsstrahlung cross-section. <BR
/>Results: It was found that the resulting electron distribution
function depends on the magnetic field assumed along the electron
beam propagation direction. For small magnetic fields the electron
distribution function becomes broad in the direction perpendicular
to the beam propagation due to the Weibel instability and the return
current is formed by the electrons in a broad and shifted bulk of
the distribution. On the other hand, for stronger magnetic fields the
distribution is more extended in the beam-propagation direction and the
return current is formed by the electrons in the extended distribution
tail. In all cases, the anisotropy of the electron distribution
decreases rapidly due to fast collisionless processes. However, the
magnetic field reduces this anisotropy decrease. The X-ray directivity
shows the same trend and it is always closer to the isotropic case
than that in a simple beaming model.
---------------------------------------------------------
Title: Response of optical hydrogen lines to beam heating. I. Electron
beams
Authors: Kašparová, J.; Varady, M.; Heinzel, P.; Karlický, M.;
Moravec, Z.
2009A&A...499..923K Altcode: 2009arXiv0904.2084K
Context: Observations of hydrogen Balmer lines in solar flares remain an
important source of information on flare processes in the chromosphere
during the impulsive phase of flares. The intensity profiles of
optically thick hydrogen lines are determined by the temperature,
density, and ionisation structure of the flaring atmosphere, by the
plasma velocities and by the velocity distribution of particles in
the line formation regions. <BR />Aims: We investigate the role of
non-thermal electrons in the formation regions of Hα, Hβ, and Hγ
lines in order to unfold their influence on the formation of these
lines. We concentrate on pulse-beam heating varying on a subsecond
timescale. Furthermore, we theoretically explore possibility that a new
diagnostic tool exists indicating the presence of non-thermal electrons
in the flaring chromosphere based on observations of optical hydrogen
lines. <BR />Methods: To model the evolution of the flaring atmosphere
and the time-dependent hydrogen excitation and ionisation, we used a
1-D radiative hydrodynamic code combined with a test-particle code that
simulates the propagation, scattering, and thermalisation of a power-law
electron beam in order to obtain the flare heating and the non-thermal
collisional rates due to the interaction of the beam with the hydrogen
atoms. To not bias the results by other effects, we calculate only
short time evolutions of the flaring atmosphere and neglect the plasma
velocities in the radiative transfer. <BR />Results: All calculated
models have shown a time-correlated response of the modelled Balmer line
intensities on a subsecond timescale, with a subsecond timelag behind
the beam flux. Depending on the beam parameters, both line centres
and wings can show pronounced intensity variations. The non-thermal
collisional rates generally result in an increased emission from a
secondary region formed in the chromosphere. <BR />Conclusions: Despite
the clear influence of the non-thermal electron beams on the Balmer line
intensity profiles, we were not able on the basis of our simulations
to produce any unambiguous diagnostic of non-thermal electrons in the
line-emitting region, which would be based on comparison of individual
Balmer line intensity profiles. However, fast line intensity variations,
well-correlated with the beam flux variations, represent an indirect
indication of pulsating beams.
---------------------------------------------------------
Title: Examples of Science Cases and Requirements for EST
Authors: Sobotka, M.; Heinzel, P.; Kašparová, J.
2009ASPC..405..455S Altcode:
We present various suggestions for the study of flares (fast emission
variations, heating mechanisms), prominences (fine structure, magnetic
field, energy balance), and sunspots (umbral structure, heating
mechanisms, depth and structure of the penumbra, Evershed flow). From
these cases we derive the requirements for the future European Solar
Telescope: spectropolarimetric capabilities, high signal-to-noise ratio,
multi-line spectroscopy, high spatial and temporal resolution.
---------------------------------------------------------
Title: Kappa distribution and hard X-ray emission of solar flares
Authors: Kašparová, J.; Karlický, M.
2009A&A...497L..13K Altcode: 2009arXiv0902.3574K
Aims: We investigate whether the so-called kappa distribution, often
used to fit electron distributions detected in situ in the solar wind,
can describe electrons producing the hard X-ray emission in solar
flares. <BR />Methods: Using Ramaty High Energy Solar Spectroscopic
imager (RHESSI) flare data we fit spatially- and feature-integrated
spectra, assuming a kappa distribution for the mean electron flux
spectrum. <BR />Results: We show that a single kappa distribution
generally cannot describe spatially integrated X-ray emission
composed of both footpoint and coronal sources. In contrast, the kappa
distribution is consistent with mean electron spectra producing hard
X-ray emission in some coronal sources.
---------------------------------------------------------
Title: Far-IR and Radio Thermal Continua in Solar Flares
Authors: Kašparová, J.; Heinzel, P.; Karlický, M.; Moravec, Z.;
Varady, M.
2009CEAB...33..309K Altcode: 2009arXiv0901.3465K
With the invention of new far-infrared (FIR) and radio mm and sub-mm
instruments (DESIR on SMESE satellite, ESO-ALMA), there is a growing
interest in observations and analysis of solar flares in this so far
unexplored wavelength region. Two principal radiation mechanisms play a
role: the synchrotron emission due to accelerated particle beams moving
in the magnetic field and the thermal emission due to the energy deposit
in the lower atmospheric layers. In this contribution we explore the
time-dependent effects of beams on thermal FIR and radio continua. We
show how and where these continua are formed in the presence of time
dependent beam heating and non-thermal excitation/ionisation of the
chromospheric hydrogen plasma.
---------------------------------------------------------
Title: Low-Energy Cutoffs in Electron Spectra of Solar Flares:
Statistical Survey
Authors: Kontar, E. P.; Dickson, E.; Kašparová, J.
2008SoPh..252..139K Altcode: 2008arXiv0805.1470K; 2008SoPh..tmp..149K
The Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) X-ray
data base (February 2002 - May 2006) has been searched to find solar
flares with weak thermal components and flat photon spectra. Using a
regularized inversion technique, we determine the mean electron flux
distribution from count spectra for a selection of events with flat
photon spectra in the 15 - 20 keV energy range. Such spectral behavior
is expected for photon spectra either affected by photospheric albedo
or produced by electron spectra with an absence of electrons in a
given energy range (e.g., a low-energy cutoff in the mean electron
spectra of nonthemal particles). We have found 18 cases that exhibit a
statistically significant local minimum (a dip) in the range of 13 - 19
keV. The positions and spectral indices of events with low-energy cutoff
indicate that such features are likely to be the result of photospheric
albedo. It is shown that if the isotropic albedo correction is applied,
all low-energy cutoffs in the mean electron spectrum are removed,
and hence the low-energy cutoffs in the mean electron spectrum of
solar flares above ∼ 12 keV cannot be viewed as real features. If
low-energy cutoffs exist in the mean electron spectra, their energies
should be less than ∼ 12 keV.
---------------------------------------------------------
Title: Hydrogen Balmer Lines in the Solar Atmosphere Heated by
Electron Beams
Authors: Kasparova, J.; Varady, M.; Moravec, Z.; Heinzel, P.;
Karlicky, M.
2008ESPM...12.3.16K Altcode:
Accelerated particle beam are one of the mechanisms of the flare
energy transport from the corona to the transition region and the
chromosphere. Such beams heat ambient plasma and may affect atomic
population via collisions. Using 1D NLTE radiative hydrodynamics
we model influence of electron beams on hydrogen Balmer lines. In
the contribution we focus on the effect of so-called non-thermal
collisional rates on Halpha and Hbeta lines. Based on our results we
discuss diagnostic methods for determination of beam presence in the
formation regions of Halpha and Hbeta lines.
---------------------------------------------------------
Title: Far-IR and Radio Continua in Solar Flares
Authors: Heinzel, P.; Kasparova, J.; Varady, M.; Karlicky, M.;
Moravec, Z.
2008ESPM...12.3.20H Altcode:
With the invention of new far-infrared (FIR) and radio mm and sub-mm
instruments (DESIR on SMESE satellite, ESO ALMA), there is a growing
interest in observations and analysis of solar flares in this so far
unexplored wavelength region. Two principal radition mechanisms play a
role: the synchrotron emission due to accelerated particle beams moving
in the magnetic field and the thermal emission due to energy deposit
in the lower atmospheric layers. The latter one was recently explored
for the case of semiempirical flare models, without considering the
temporal evolution. However, as the radiation-hydrodynamical simulations
do show, the lower atmosphere heated by beams exhibits fast temporal
changes which are typically reflected in variations of spectral-line
intensities. In this contribution we explore the time-dependent effects
of beams on FIR and radio continua. We show how and where these
continua are formed in the presence of time dependent beam heating
and non-thermal excitation/ionization of the chromospheric hydrogen
plasma. Our results should contribute to planning of new observations
in FIR and radio domain.
---------------------------------------------------------
Title: Fast spectral fitting of hard X-ray bremsstrahlung from
truncated power-law electron spectra
Authors: Brown, J. C.; Kašparová, J.; Massone, A. M.; Piana, M.
2008A&A...486.1023B Altcode: 2008arXiv0802.0621B
Context: Hard X-ray bremsstrahlung continuum spectra, such as from solar
flares, are commonly described in terms of power-law fits, either to the
photon spectra themselves or to the electron spectra responsible for
them. In applications various approximate relations between electron
and photon spectral indices are often used for energies both above
and below electron low-energy cutoffs. <BR />Aims: We examine the
form of the exact relationships in various situations, and for various
cross-sections, showing that empirical relations sometimes used can be
highly misleading especially at energies below the low-energy cutoff,
and consider how to improve fitting procedures. <BR />Methods: We
obtain expressions for photon spectra from single, double and truncated
power-law electron spectra for a variety of cross-sections and for
the thin and thick target models and simple analytic expressions for
the non-relativistic Bethe-Heitler case. <BR />Results: We show that
below the low-energy cutoff Kramers and other constant spectral index
forms commonly used are very poor approximations to accurate results,
but that our analytical forms are a good match; and that above a
low-energy cutoff, the Kramers and non-relativistic Bethe-Heitler
results match reasonably well with results for up to energies around
100 keV. <BR />Conclusions: Analytical forms of the non-relativistic
Bethe-Heitler photon spectra from general power-law electron spectra
are good match to exact results for both thin and thick targets and
they enable much faster spectral fitting than evaluation of the full
spectral integrations.
---------------------------------------------------------
Title: Modelling of Optical Emission in Solar Flares
Authors: Varady, M.; Kašparová, J.; Heinzel, P.; Karlický, M.;
Moravec, Z.
2008CEAB...32..101V Altcode:
We present recent progress achieved by our group in the field of flare
optical emission modelling. We concentrate on two problems. Firstly,
on the possibility of modelling of the time evolution of several Balmer
line profiles calculated for real electron fluxes obtained from the hard
X--ray observations of a particular flare with the prospect to compare
the theoretical results with the observed data for the corresponding
flare. Secondly, we discuss the influence of the non--thermal electrons
in the line emitting region on the formation and time evolution of
Balmer hydrogen line profiles.
---------------------------------------------------------
Title: Low-Energy Cut-Offs In Electron Spectra Of Solar Flares:
Statistical Survey
Authors: Kontar, Eduard; Dickson, Ewan; Kasparova, Jana
2008cosp...37.1577K Altcode: 2008cosp.meet.1577K
Ramaty High Energy Solar Spectroscopic Imager (RHESSI) X-ray data base
(February 2002 - May 2006) has been searched to find solar flares with
weak thermal component and flat photon spectra. Using a regularised
inversion technique, we determine the mean electron flux distribution
from count spectra of the events which had flat photon spectra in
the 15-20 keV energy range. Such spectral behaviour is expected for
photon spectra either affected by photospheric albedo or produced by
electron spectra with an absence of electrons in some energy range,
e.g. low-energy cutoff in electron spectra. We have found a number of
cases which exhibit a statistically significant dip in the range of
10-20 keV. The positions and spectral indices of events with low-energy
cutoffs indicate that such feature could be a result of photospheric
albedo. It is shown that if the isotropic albedo correction was applied,
all low-energy cutoffs in mean electron spectrum were removed.
---------------------------------------------------------
Title: Hydrogen Balmer line formation in solar flares affected by
return currents
Authors: Štepán, J. Å.; Kašparová, J.; Karlický, M.; Heinzel, P.
2007A&A...472L..55S Altcode: 2007arXiv0708.0265S
Aims:We investigate the effect of the electric return currents in
solar flares on the profiles of hydrogen Balmer lines. We consider the
monoenergetic approximation for the primary beam and runaway model of
the neutralizing return current. <BR />Methods: Propagation of the
10 keV electron beam from a coronal reconnection site is considered
for the semiempirical chromosphere model F1. We estimate the local
number density of return current using two approximations for beam
energy fluxes between 4 × 10<SUP>11</SUP> and 1 × 10<SUP>12</SUP>
erg cm<SUP>-2</SUP> s<SUP>-1</SUP>. Inelastic collisions of beam and
return-current electrons with hydrogen are included according to their
energy distributions, and the hydrogen Balmer line intensities are
computed using an NLTE radiative transfer approach. <BR />Results:
In comparison to traditional NLTE models of solar flares that neglect
the return-current effects, we found a significant increase emission
in the Balmer line cores due to nonthermal excitation by return
current. Contrary to the model without return current, the line
shapes are sensitive to a beam flux. It is the result of variation
in the return-current energy that is close to the hydrogen excitation
thresholds and the density of return-current electrons.
---------------------------------------------------------
Title: Hα with Heating by Particle Beams
Authors: Kašparová, J.; Varady, M.; Karlický, M.; Heinzel, P.;
Moravec, Z.
2007ASPC..368..441K Altcode: 2007astro.ph..3800K
Using 1D NLTE radiative hydrodynamics we model the influence of the
particle beams on the Hα line profile treating the beam propagation and
the atmosphere evolution self-consistently. We focus on the influence
of the non-thermal collisional rates and the return current. Based on
our results, we propose a diagnostic method for determination of the
particle beam presence in the formation regions of the Hα line.
---------------------------------------------------------
Title: Hard X-ray spectra and positions of solar flares observed by
RHESSI: photospheric albedo, directivity and electron spectra
Authors: Kašparová, J.; Kontar, E. P.; Brown, J. C.
2007A&A...466..705K Altcode: 2007astro.ph..1871K
Aims:We investigate the signature of the photospheric albedo
contribution in solar flare hard X-ray spectra, the effect of low
energy cutoffs in electron spectra, and the directivity of hard X-ray
emission. <BR />Methods: Using Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) flare data we perform a statistical analysis of
spatially integrated spectra and positions of solar flares. <BR
/>Results: We demonstrate clear centre-to-limb variation of photon
spectral indices in the 15-20 keV energy range and a weaker dependency
in the 20-50 keV range which is consistent with photospheric albedo as
the cause. The results also suggest that low-energy cutoffs sometimes
inferred in mean electron spectra are an artefact of albedo. We also
derive the anisotropy (ratio of downward/observer directed photons)
of hard X-ray emission in the 15-20 keV range for various heliocentric
angles.
---------------------------------------------------------
Title: Return Current and Energy Deposit in Flares
Authors: Varady, M.; Karlický, M.; Kašparová, J.
2007ASPC..368..473V Altcode:
The return current (RC) related effects represent in flares one
of the possible mechanisms of conversion of the kinetic energy of
electron beams into the thermal energy of flare plasma. Using a 1-D
current-in-cell model, details of formation and properties of the RC
driven by monoenergetic electron beams are calculated. Based on results
of the simulations, the influence of the RC on the energy deposit in
flares is discussed.
---------------------------------------------------------
Title: Optical and UV Emission of Solar Flares: Multiwavelength
Observations and Modelling
Authors: Kasparova, J.; Heinzel, P.
2007AGUSMSH22A..07K Altcode:
Solar flares reveal themselves in various ranges of electromagnetic
emission and exhibit temporal variations down to sub-second scale,
namely during the so-called impulsive phase. This contribution will
focus on spatial and temporal variations of the optical and UV emissions
which are thought to be driven by flare energy transport in the form
of accelerated particles. We will review our current understanding
of the formation of optical and UV emissions during the impulsive
phase. Namely, we will discuss recent radiative-hydrodynamic models
and various physical processes playing an important role in radiation
transfer and formation of optical and UV spectra. We will also report on
recent interpretations of observations in various lines and continua and
discuss their importance for the diagnostics of the flare atmosphere
structure and the presence of accelerated particles in the emission
formation regions.
---------------------------------------------------------
Title: RHESSI survey of photospheric albedo and directivity of solar
flare hard X-ray spectra
Authors: Kasparova, J.; Kontar, E. P.
2006IAUJD...1E..48K Altcode:
Hard X-ray spectra of solar flares are generated as bremsstrahlung
of accelerated electrons propagating in solar corona. The photons
emitted towards the photosphere have a high probability to undergo
Compton backscattering into observers direction. They form so called
photospheric albedo component and modify the spatially integrated
photon spectra of solar flares. Analysing 409 solar flares observed
by RHESSI, we show significant centre-to-limb variation of observed
photon spectra in energies ~ 20 keV, which is consistent with the
photospheric albedo. Moreover, we also show that the low-energy cutoff
in the mean electron spectrum can be viewed as an artifact of the
albedo component. Noting that the amount of backscattered photons
strongly depends on the downward directed photon flux, we determine
for the first time the directivity of the downward photon flux. The
results favour near-isotropic photon distribution and represent a
problem for the models with downward propagating electron beam.
---------------------------------------------------------
Title: Return Current And The Energy Deposit In Flares
Authors: Varady, M.; Karlicky, M.; Kasparova, J.
2006IAUJD...1E..51V Altcode:
The return current related effects in flares represent one of the
possible mechanisms of conversion of the kinetic energy of electron
beams into the thermal energy of flare plasma. Using a 1-D particle in
cell model details of formation and properties of the return current
driven by monoenergetic electron beams are calculated. Using the results
of the simulations the influence of the return current on the energy
deposit in flares are discussed.
---------------------------------------------------------
Title: Polarization Diagnostics of Proton Beams in Solar Flares
Authors: Stepan, J.; Heinzel, P.; Kasparova, J.; Sahal-Brechot, S.
2006IAUJD...1E..55S Altcode:
We review the problem of proton beam bombardment of solar chromosphere
considering the self-consistent NLTE polarized radiation transfer in
hydrogen lines. Several observations indicate a linear polarization
of H-alpha line of the order of 5% or higher and preferentially in
radial direction. This polarization is often explained as anisotropic
collisional excitation of the n= 3 level by vertical proton beams. Our
calculations indicate that deceleration of the proton beam with initial
power-law energy distribution together with increased electron and
proton densities in H-alpha forming layers lead to negligible line
polarization. Thus the proton beams seem not to be a good candidate
for explanation of the observed polarization degree.
---------------------------------------------------------
Title: On AN Effect of Particle Beams on Correlation Between Balmer
Series Lines
Authors: Kashapova, L. K.; Kotrč, P.; Kupryakov, Yu. A.; Kašparová,
J.
2005ESASP.600E.126K Altcode: 2005dysu.confE.126K; 2005ESPM...11..126K
No abstract at ADS
---------------------------------------------------------
Title: Problem of the Return Current in Energy Deposit in Flares
Authors: Varady, M.; Karlický, M.; Kašparová, J.
2005ESASP.600E.146V Altcode: 2005ESPM...11..146V; 2005dysu.confE.146V
No abstract at ADS
---------------------------------------------------------
Title: Hα Line in Solar Atmosphere Heated by Particle Beams
Authors: Kašparová, J.; Varady, M.; Karlický, M.; Moravec, Z.;
Heinzel, P.
2005ESASP.600E.127K Altcode: 2005dysu.confE.127K; 2005ESPM...11..127K
No abstract at ADS
---------------------------------------------------------
Title: Multi-Wavelength Analysis of High-Energy Electrons in Solar
Flares: A Case Study of the August 20, 2002 Flare
Authors: Kašparová, Jana; Karlický, Marian; Kontar, Eduard P.;
A. Schwartz, Richard; Dennis, Brian R.
2005SoPh..232...63K Altcode: 2005astro.ph..8636K
A multi-wavelength spatial and temporal analysis of solar high-energy
electrons is conducted using the August 20, 2002 flare of an unusually
flat (γ<SUB>1</SUB> = 1.8) hard X-ray spectrum. The flare is studied
using RHESSI, Hα, radio, TRACE, and MDI observations with advanced
methods and techniques never previously applied in the solar flare
context. A new method to account for X-ray Compton backscattering in the
photosphere (photospheric albedo) has been used to deduce the primary
X-ray flare spectra. The mean electron flux distribution has been
analysed using both forward fitting and model-independent inversion
methods of spectral analysis. We show that the contribution of the
photospheric albedo to the photon spectrum modifies the calculated mean
electron flux distribution, mainly at energies below ∼100 keV. The
positions of the Hα emission and hard X-ray sources with respect to
the current-free extrapolation of the MDI photospheric magnetic field
and the characteristics of the radio emission provide evidence of the
closed geometry of the magnetic field structure and the flare process in
low altitude magnetic loops. In agreement with the predictions of some
solar flare models, the hard X-ray sources are located on the external
edges of the Hα emission and show chromospheric plasma heated by the
non-thermal electrons. The fast changes of Hα intensities are located
not only inside the hard X-ray sources, as expected if they are the
signatures of the chromospheric response to the electron bombardment,
but also away from them.
---------------------------------------------------------
Title: X-Ray and HαEmission of the 20 Aug 2002 Flare*
Authors: Kašparová, J.; Karlický, M.; Schwartz, R. A.; Dennis, B. R.
2005ASSL..320..187K Altcode: 2005smp..conf..187K
No abstract at ADS
---------------------------------------------------------
Title: Collisional excitation and ionization of hydrogen by return
current in solar flares
Authors: Karlický, M.; Kašparová, J.; Heinzel, P.
2004A&A...416L..13K Altcode:
First a problem of the transport of electron beams with high energy
fluxes into the cold chromosphere during the flare is presented. Then
it is shown that the problem might be solved by the return current
formed by superthermal (runaway) electrons. In such a case the
return current electrons could influence hydrogen excitations and
ionizations. Therefore, we computed collisional rates of such a
return current and compared them with those of the thermal plasma
and of a monoenergetic (10 keV) electron beam with the energy flux
F<SUB>E</SUB> = 10<SUP>12</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>
penetrating into the flare atmosphere described by the F1 model (Machado
et al. \cite{Machado1980}). We show that in this situation the return
current collisional rates can be dominant for some transitions.
---------------------------------------------------------
Title: Collisional Excitation and Ionization of Hydrogen by Return
Current in Solar Flares
Authors: Kašparová, J.; Heinzel, P.; Karlický, M.
2004IAUS..219..760K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Analysis and modelling of hard X-ray and optical signatures
of electron beams in solar flares
Authors: Kasparova, Jana
2004PhDT.......563K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Unusual Hard X-ray Spectrum of the Flare of 20 August 2002
Authors: Schwartz, R. A.; Kasparova, J.; Dennis, B.; Karlicky, M.
2003AGUFMSH22A0171S Altcode:
An M3 Class flare was observed in x-rays with RHESSI and in H-alpha
with the Kanzelhohe Solar Observatory. The event was observed to
several hundreds of keV in X-rays and was marked by an unusually flat
spectrum observed from 20-70 keV. The measured power-law exponent
of this component was about 1.7, very close to the theoretical limit
for a thick-target injection of energetic electrons implying a near
cutoff below 80 keV. We will bound any systematic effects that may be
contributing to this result by analyzing the spectrum using multiple
techniques. We will also forward model the spatial/spectral x-ray
sources to further validate these observations.
---------------------------------------------------------
Title: Time-dependent Flare Models with MALI
Authors: Kašparová, J.; Heinzel, P.; Varady, M.; Karlický, M.
2003ASPC..288..544K Altcode: 2003sam..conf..544K
Temporal variations of Hα line profile intensities related to electron
beams are presented. We show first results of time dependent simulations
of a chromospheric response to a 1 sec monoenergetic electron beam. 1-D
hydrodynamic code together with particle representation of the beam have
been used to calculate atmospheric evolution. Time dependent radiative
transfer problem has been solved for the resulting atmosphere in the
MALI approach, using the Crank-Nicholson implicit scheme. Non-thermal
collisional rates were included in linearised equations of statistical
equilibrium.
---------------------------------------------------------
Title: Time dependent flare model with non-LTE radiative transfer
Authors: Varady, M.; Karlický, M.; Kašparová, J.; Heinzel, P.
2002ESASP.506..521V Altcode: 2002svco.conf..521V; 2002ESPM...10..521V
The first results of a time dependent simulation of chromospheric
response to a high energy electron beam are presented. The hybrid code,
i.e. a combination of a 1-D hydrodynamic code and a test particle code,
has been used to calculate the energy losses of a high energy electron
beam propagating through the solar atmosphere and the consequent
response of the ambient solar plasma to the energy deposition. The
resulting time evolution of the solar plasma temperature, density,
velocity and energy deposit on hydrogen has then been used as an input
for a time dependent radiative transfer code in the MALI approach
to determine the time variation of the Hα line profile. Non-thermal
collisional rates have been included in the linearised ESE.
---------------------------------------------------------
Title: Diagnostics of electron bombardment in solar flares from
hydrogen Balmer lines
Authors: Kašparová, J.; Heinzel, P.
2002A&A...382..688K Altcode:
Influence of non-thermal collisional rates, related to an electron
beam, on hydrogen Balmer line profiles is investigated. Semi-empirical
temperature structure of the flare model F1 has been used for computing
non-LTE profiles of Hα , Hβ , and Hγ . Contribution functions
and their change due to different values of beam parameters are
shown. Unlike the line core intensity, the intensity of line wings
considerably depends on beam parameters and it is significantly
enhanced for typical values of the beam energy flux. The ratio of
line intensities at a selected wavelength is proposed to be used for
diagnostics of electron beams during solar flares, particularly at
impulsive phases. Obtained Hα line profiles are compared to those of
Fang et al. (\cite{fhg93}).
---------------------------------------------------------
Title: Physical Characteristics of the September 23, 1998 Solar Flare
Authors: Kotrc, P.; Karlický, M.; Kupryakov, Yu. A.; Kaltman, T. I.;
Kasparova, J.; Rompolt, B.
1999ESASP.448..841K Altcode: 1999ESPM....9..841K; 1999mfsp.conf..841K
No abstract at ADS
---------------------------------------------------------
Title: New Evidence of Chromospheric Evaporation
Authors: Kasparova, J.; Kotrc, P.; Heinzel, P.; Nikulin, I. F.;
Rudawy, P.
1998ASPC..150..397K Altcode: 1998IAUCo.167..397K; 1998npsp.conf..397K
No abstract at ADS
