Author name code: kato ADS astronomy entries on 2022-09-14 =author:"Kato, Yoshiaki" ------------------------------------------------------------------------ Title: Comments on "Imaging Reanalyses of EHT Data" Authors: Miyoshi, Makoto; Kato, Yoshiaki; Makino, Jun Bibcode: 2022arXiv220713279M Altcode: On June 14, 2022, the EHT collaboration (hereafter EHTC) made the web page (https://eventhorizontelescope.org/blog/imaging-reanalyses-eht-data) with the title "Imaging Reanalyses of EHT Data," in which they made comments on our recent Miyoshi et al .2022 published in the Astrophysical Journal. We investigated the EHTC comments and found that all of the five points raised by the EHTC are subjective and unsubstantiated claims. Thus they do not prove the correctness of the result of EHTC. Sincerely we hope that the EHTC will publish, not a collection of unsubstantiated claims, but a discussion based on scientific arguments. Title: Radiation Magnetohydrodynamic Simulations of sub-Eddington accretion flows in AGN Authors: Igarashi, Taichi; Matsumoto, Yosuke; Matsumoto, Ryoji; Kato, Yoshiaki; Takahashi, Hiroyuki; Ohsuga, Ken Bibcode: 2022cosp...44.2284I Altcode: The origin of the soft X-ray excess in luminous active galactic nuclei (AGN) such as type 1 Seyfert galaxies is thought to be the warm Compton region with a temperature of $10^{6}-10^{7}$ K. This temperature is higher than that of the optically thick standard disk around a supermassive black hole and lower than the optically thin and radiatively inefficient accretion flow (RIAF). Recently, transitions between a hard X-ray dominant state and a soft X-ray dominant state have been observed in changing look AGN, which changes between type 1 with broad emission lines and type 2 without broad emission lines. This hard-to-soft state transition is similar to the state transitions observed in stellar-mass black hole candidates. The origin of the state transition may be the cooling instability which grows when the accretion rate exceeds the upper limit of RIAF. Igarashi et al. (2020) reported the results of global three-dimensional radiation magnetohydrodynamic simulations of the accretion flow into a supermassive black hole carried out by using a radiation magnetohydrodynamic code CANS+R. They found that when the accretion rate exceeds 10% of the Eddington accretion rate, a warm Compton region with a temperature of $10^{7}-10^{8}$ K is formed outside the RIAF near the black hole and that radial oscillation is excited in this region when the radiation pressure becomes dominant. The critical luminosity for this transition is 0.5% of the Eddington luminosity, which is consistent with observations of changing look AGN. However, the temperature of the warm region is higher than that of the soft X-ray emitting region of AGN obtained by using the observed radiation spectra. Here we report the results of radiation magnetohydrodynamic simulations carried out by implementing the effects of Compton cooling to the CANS+R code. As a result, the temperature of the Thomson thick, warm Compton region decreased to $10^{6}-10^{7}$ K. We discuss the structure and time variation of the warm Compton region. Title: The Jet and Resolved Features of the Central Supermassive Black Hole of M87 Observed with the Event Horizon Telescope (EHT) Authors: Miyoshi, Makoto; Kato, Yoshiaki; Makino, Junichiro Bibcode: 2022ApJ...933...36M Altcode: 2022arXiv220504623M We report the result of our independent image reconstruction of the M87 from the public data of the Event Horizon Telescope Collaborators (EHTC). Our result is different from the image published by the EHTC. Our analysis shows that (a) the structure at 230 GHz is consistent with those of lower-frequency very long baseline interferometry observations, (b) the jet structure is evident at 230 GHz extending from the core to a few milliarcsecond, although the intensity rapidly decreases along the axis, and (c) the "unresolved core" is resolved into three bright features presumably showing an initial jet with a wide opening angle of ~70°. The ring-like structures of the EHTC can be created not only from the public data but also from the simulated data of a point image. Also, the rings are very sensitive to the field-of-view (FOV) size. The u-v coverage of the Event Horizon Telescope (EHT) lacks ~ 40 μas fringe spacings. Combining with a very narrow FOV, it created the ~40 μas ring structure. We conclude that the absence of the jet and the presence of the ring in the EHTC result are both artifacts owing to the narrow FOV setting and the u-v data sampling bias effect of the EHT array. Because the EHTC's simulations only take into account the reproduction of the input image models, and not those of the input noise models, their optimal parameters can enhance the effects of sampling bias and produce artifacts such as the ~40 μas ring structure, rather than reproducing the correct image. Title: Wakefield Acceleration in a Jet from a Neutrino-driven Accretion Flow around a Black Hole Authors: Kato, Yoshiaki; Ebisuzaki, Toshikazu; Tajima, Toshiki Bibcode: 2022ApJ...929...42K Altcode: 2022arXiv220111755K We have investigated electromagnetic (EM) wave pulses in a jet from a neutrino-driven accretion flow (NDAF) around a black hole (BH). NDAFs are massive accretion disks whose accretion rates are $\dot{M}\,\approx $ 0.01-10 M ⊙ s-1 for stellar-mass BHs. Such an extreme accretion may produce a collimated relativistic outflow like a magnetically driven jet in active galactic nuclei and microquasars. When we consider strong toroidal magnetic field stranded in the inner region of an NDAF disk and magnetic impulses on the jet, we find that they lead to the emanation of high-energy emissions for gamma-ray bursts, as well as high-energy cosmic rays. When Alfvénic wave pulses are generated by episodic immense accretions, they propagate along the large-scale structured magnetic field in the jet. Once the Alfvénic wave pulses reach nearly the speed of light in the underdense condition, they turn into EM wave pulses, which produce plasma wakes behind them. These wakefields exert a collective accelerating force synchronous to the motion of particles. As a result, the wakefield acceleration premises various observational signatures, such as pulsating bursts of high-energy gamma rays from accelerated electrons, pulses of neutrinos from accelerated protons, and protons with maximum energies beyond 1020 eV. Title: X-ray laser development at the Institute of Laser Engineering, Osaka University with worldwide collaboration Authors: Kato, Yoshiaki; Daido, Hiroyuki Bibcode: 2021SPIE11886E..0DK Altcode: This paper presents a brief review of the x-ray laser development at the Institute of Laser Engineering, Osaka University, implemented with worldwide collaboration. The scaling of the x-ray lasing toward shorter wavelengths has been investigated in the recombination-pumped (RP) and electron-collisional-excitation (CE) pumped x-ray lasers. Extension of the RP x-ray laser close to the water window is described. With the CE x-ray laser, intense lasing of the J = 0-1 line at 19.6 nm in the neon-like Ge ion and lasing over 14.3 - 4.5 nm with the nickel-like ions are reported. Spectroscopic studies of the x-ray lasers are described, including the first observation of polarization of the x-ray laser beam generated by amplified spontaneous emission. The perspective of the plasma-based x-ray lasers is also presented. Title: Wakefield Acceleration in a Jet from a Neutrino Driven Accretion Flow around a Black Hole Authors: Kato, Yoshiaki; Ebisuzaki, Toshikazu; Tajima, Toshiki Bibcode: 2021APS..DPPJP1012K Altcode: We have investigated electromagnetic pulses in a jet from a neutrino driven accretion flow (NDAF) around a black hole. NDAFs are massive accretion disks of accretion rates M ~ 0.01-10M⊙/s for black holes of several solar masses M <= 10M⊙, such extreme accretions are investigated as a model of gamma-ray bursts (GRBs) as well as supernovae and hypernovae. Recently, Ebisuzaki & Tajima 2019 (ET19) have proposed a model of acceleration mechanism of charged particles to very high energies ~ 1020 eV by electromagnetic wave-particle interaction. If episodic eruptive accretions generate Alfv ́enic pulses along large-scale structured magnetic field in the jet, such Alfv ́enic pulses act as a driver of the collective accelerating pondermotive forces which drive the wakes whose direction is parallel to the motion of particles. Because the wakes propagate at the same speed with the particles, the so-called wakefield acceleration has a robust built-in coherence by the acceleration system itself. In this study we extend a model of the accretion disk presented by ET19 into a NDAF. We estimate the energy flux of both the electro-magnetic wave pulses and neutrino emissions from the NDAFs. We find that the total luminosity of waves Lwave = Mc2 / ?? √ 18α2β3 and the that of neutrinos Lν = Mc2 / 4 where α and β are the viscosity parameter and the plasma-β of the disk, respectively. The properties of the NDAFs and magnetically driven jets as well as the maximum energy of accelerated charged particles will be discussed. Title: Radiation Magnetohydrodynamic Simulations of Black Hole Accretion Flows in Bright Hard State Authors: Igarashi, Taichi; Matsumoto, Yosuke; Matsumoto, Ryoji; Kato, Yoshiaki; Takahashi, Hiroyuki; Ohsuga, Ken Bibcode: 2021cosp...43E1550I Altcode: Bright hard states are observed during the outbursts of stellar mass black hole candidates. This state appears when the luminosity exceeds 0.1% of the Eddington luminosity in the hard X-ray dominant state. When the luminosity increase further, the black hole candidate transit to the soft X-ray dominant state. Such a transition is called hard-to-soft transitions. Similar state transitions are observed in AGNs. In some Seyfert galaxies, soft X-ray excess component appears when the luminosity exceeds 0.1% of the Eddington luminosity. Furthermore, rapid time variabilities are observed during the hard-to-soft state transition. Since the luminosity of the bright hard state exceeds the upper limit for radiatively inefficient accretion flows (RIAFs), radiative cooling should be taken into account to simulate the accretion flow in this state. We carried out 3D radiation magnetohydrodynamic simulations of the hard-to-soft state transition. The initial disk density is determined, such that the mass accretion rate is around 10% of the Eddington accretion rate. We found that radiation pressure dominant, relatively cool (T $<$$ 10^{8}$ K) region appears outside the optically thin, hot accretion flow near the black hole. We also found that the radiation pressure dominant region oscillates quasi-periodically. The possible mechanism of the oscillation is the radial pulsational instability (e.g., Kato 1978; Blumenthal et al. 1984). In this talk, we discuss the possibility that the non-axisymmetric radial pulsation in the radiation pressure dominant region is the origin of low frequency QPOs in black hole candidates and rapid time variabilities in changing look AGNs. Title: Radiation Magnetohydrodynamic Simulations of Sub-Eddington Accretion Flows in AGNs: Origin of Soft X-Ray Excess and Rapid Time Variabilities Authors: Igarashi, Taichi; Kato, Yoshiaki; Takahashi, Hiroyuki R.; Ohsuga, Ken; Matsumoto, Yosuke; Matsumoto, Ryoji Bibcode: 2020ApJ...902..103I Altcode: 2020arXiv200905813I We investigate the origin of the soft X-ray excess component in Seyfert galaxies observed when their luminosity exceeds 0.1% of the Eddington luminosity ( ${L}_{\mathrm{Edd}}$ ). The evolution of a dense blob in radiatively inefficient accretion flow (RIAF) is simulated by applying a radiation magnetohydrodynamic code, CANS+R. When the accretion rate onto a ${10}^{7}\,{M}_{\odot }$ black hole exceeds 10% of the Eddington accretion rate ( ${\dot{M}}_{\mathrm{Edd}}={L}_{\mathrm{Edd}}/{c}^{2}$ , where c is the speed of light), the dense blob shrinks vertically because of radiative cooling and forms a Thomson thick, relatively cool (∼107-8 K) region. The cool region coexists with the optically thin, hot ( $T\sim {10}^{11}\,{\rm{K}}$ ) RIAF near the black hole. The cool disk is responsible for the soft X-ray emission, while hard X-rays are emitted from the hot inner accretion flow. Such a hybrid structure of hot and cool accretion flows is consistent with the observations of both hard and soft X-ray emissions from "changing-look" active galactic nuclei (CLAGNs). Furthermore, we find that quasi-periodic oscillations (QPOs) are excited in the soft X-ray-emitting region. These oscillations can be the origin of rapid X-ray time variabilities observed in CLAGNs. Title: Chromospheric and Coronal Wave Generation in a Magnetic Flux Sheath Authors: Kato, Yoshiaki; Steiner, Oskar; Hansteen, Viggo; Gudiksen, Boris; Wedemeyer, Sven; Carlsson, Mats Bibcode: 2016ApJ...827....7K Altcode: 2016arXiv160608826K Using radiation magnetohydrodynamic simulations of the solar atmospheric layers from the upper convection zone to the lower corona, we investigate the self-consistent excitation of slow magneto-acoustic body waves (slow modes) in a magnetic flux concentration. We find that the convective downdrafts in the close surroundings of a two-dimensional flux slab “pump” the plasma inside it in the downward direction. This action produces a downflow inside the flux slab, which encompasses ever higher layers, causing an upwardly propagating rarefaction wave. The slow mode, excited by the adiabatic compression of the downflow near the optical surface, travels along the magnetic field in the upward direction at the tube speed. It develops into a shock wave at chromospheric heights, where it dissipates, lifts the transition region, and produces an offspring in the form of a compressive wave that propagates further into the corona. In the wake of downflows and propagating shock waves, the atmosphere inside the flux slab in the chromosphere and higher tends to oscillate with a period of ν ≈ 4 mHz. We conclude that this process of “magnetic pumping” is a most plausible mechanism for the direct generation of longitudinal chromospheric and coronal compressive waves within magnetic flux concentrations, and it may provide an important heat source in the chromosphere. It may also be responsible for certain types of dynamic fibrils. Title: The statistical properties of vortex flows in the solar atmosphere Authors: Wedemeyer, Sven; Kato, Yoshiaki; Steiner, Oskar Bibcode: 2015IAUGA..2256852W Altcode: Rotating magnetic field structures associated with vortex flows on the Sun, also known as “magnetic tornadoes”, may serve as waveguides for MHD waves and transport mass and energy upwards through the atmosphere. Magnetic tornadoes may therefore potentially contribute to the heating of the upper atmospheric layers in quiet Sun regions.Magnetic tornadoes are observed over a large range of spatial and temporal scales in different layers in quiet Sun regions. However, their statistical properties such as size, lifetime, and rotation speed are not well understood yet because observations of these small-scale events are technically challenging and limited by the spatial and temporal resolution of current instruments. Better statistics based on a combination of high-resolution observations and state-of-the-art numerical simulations is the key to a reliable estimate of the energy input in the lower layers and of the energy deposition in the upper layers. For this purpose, we have developed a fast and reliable tool for the determination and visualization of the flow field in (observed) image sequences. This technique, which combines local correlation tracking (LCT) and line integral convolution (LIC), facilitates the detection and study of dynamic events on small scales, such as propagating waves. Here, we present statistical properties of vortex flows in different layers of the solar atmosphere and try to give realistic estimates of the energy flux which is potentially available for heating of the upper solar atmosphere Title: Measuring energy flux of magneto-acoustic wave in the magnetic elements by using IRIS Authors: Kato, Yoshiaki; De Pontieu, Bart; Martinez-Sykora, Juan; Hansteen, Viggo; Pereira, Tiago; Leenaarts, Jorritt; Carlsson, Mats Bibcode: 2014cosp...40E1423K Altcode: NASA's Interface Region Imaging Spectrograph (IRIS) has opened a new window to explore the chromospheric/coronal waves that potentially energize the solar atmosphere. By using an imaging spectrograph covering the Si IV and Mg II h&k lines as well as a slit-jaw imager centered at Si IV and Mg II k onboard IRIS, we can determine the nature of propagating magneto-acoustic waves just below and in the transition region. In this study, we compute the vertically emergent intensity of the Si IV and Mg II h&k lines from a time series of snapshots of a magnetic element in a two-dimensional Radiative MHD simulation from the Bifrost code. We investigate the synthetic line profiles to detect the slow magneto-acoustic body wave (slow mode) which becomes a slow shock at the lower chromosphere in the magnetic element. We find that the Doppler shift of the line core gives the velocity amplitude of the longitudinal magneto-acoustic body wave. The contribution function of the line core indicates that the formation of Mg II h&k lines is associated with the propagating shocks and therefore the time evolution of the line core intensity represents the propagating shocks projected on the optical surface. We will report on measurement of the energy flux of slow modes in the magnetic elements by using IRIS observations. Title: Saturation of Stellar Winds from Young Suns Authors: Suzuki, Takeru K.; Imada, Shinsuke; Kataoka, Ryuho; Kato, Yoshiaki; Matsumoto, Takuma; Miyahara, Hiroko; Tsuneta, Saku Bibcode: 2013PASJ...65...98S Altcode: 2012arXiv1212.6713S We investigated mass losses via stellar winds from Sun-like main-sequence stars with a wide range of activity levels. We performed forward-type magnetohydrodynamical numerical experiments for Alfvén wave-driven stellar winds with a wide range of input Poynting flux from the photosphere. Increasing the magnetic field strength and the turbulent velocity at the stellar photosphere from the current solar level, the mass-loss rate rapidly at first increases, owing to suppression of the reflection of the Alfvén waves. The surface materials are lifted up by the magnetic pressure associated with the Alfvén waves, and the cool dense chromosphere is intermittently extended to 10%#8211;20% of the stellar radius. The dense atmospheres enhance the radiative losses, and eventually most of the input Poynting energy from the stellar surface escapes by radiation. As a result, there is no more sufficient energy remaining for the kinetic energy of the wind; the stellar wind saturates in very active stars, as observed in Wood et al. (2002, ApJ, 574, 412; 2005, ApJ, 628, L143). The saturation level is positively correlated with Br,0 f0, where Br,0 and f0 are the magnetic field strength and the filling factor of open flux tubes at the photosphere. If Br,0 f0 is relatively large gtrsim 5 G, the mass-loss rate could be as high as 1000 times. If such a strong mass loss lasts for ∼ 1 billion years, the stellar mass itself would be affected, which could be a solution to the faint young Sun paradox. We derived a Reimers-type scaling relation that estimates the mass-loss rate from an energetics consideration of our simulations. Finally, we derived the evolution of the mass-loss rates, dot;{M} ∝ t-1.23, of our simulations, combining with an observed time evolution of X-ray flux from Sun-like stars, which are shallower than dot;{M} ∝ t-2.33±0.55 in Wood et al. (2005). Title: First phase observations of the enormous flare due to vast mass infall onto the Sgr A* black hole Authors: Asaki, Yoshiharu; Dodson, Richard; Miyoshi, Makoto; Tsuboi, Masato; Oka, Tomoharu; Horiuchi, Shinji; Nishiyama, Shogo; Yonekura, Yoshinori; Kato, Yoshiaki; Takaba, Hiroshi; Miyamoto, Yusuke; Takahashi, Masaaki; Saida, Hiromi; Takekawa, Shunya; Sekido, Mamoru; Kameya, Osamu Bibcode: 2013atnf.prop.5778A Altcode: We propose to perform the first phase observations of the enormous flare due to vast mass infall onto the Sgr A* black hole using the ATCA at 15, 7, and 3 mm bands in order to record the spectacular event as soon as possible after the Sgr A* flare-up event observed from our daily monitor systems in radio using the Japanese VLBI and in near-infrared (NIR) using a 1.4-m telescope (J, H, Ks) in South Africa. Title: First phase observations of the enormous flare due to vast mass infall onto the Sgr A* black hole Authors: Asaki, Yoshiharu; Miyoshi, Makoto; Tsuboi, Masato; Horiuchi, Shinji; Nishiyama, Shogo; Yonekura, Yoshinori; Kato, Yoshiaki; Takaba, Hiroshi; Miyamoto, Yusuke; Takahashi, Masaaki; Saida, Hiromi Bibcode: 2013atnf.prop.5501A Altcode: We propose to perform the first phase observations of the enormous flare due to vast mass infall onto the Sgr A* black hole using the ATCA at 15, 7, and 3~mm bands in order to record the spectacular event as soon as possible after our detection of the flare-up event of Sgr A* from daily monitoring in radio using the Japanese short-baseline VLBI and in near-infrared (NIR) using a 1.4-m telescope (J, H, Ks) in South Africa. We have obtained Target-of-Opportunity (ToO) time of telescopes from radio to infrared for the same science target, so that we will be tackling on the first phase of the event in the wide frequency range. Title: First phase observations of the enormous flare due to vast mass infall onto the Sgr A* black hole Authors: Miyoshi, Makoto; Tsuboi, Masato; Yonekura, Yoshinori; Asaki, Yoshiharu; Kato, Yoshiaki; Takaba, Hiroshi; Miyamoto, Yusuke; Takahashi, Masaaki; Saida, Hiromi Bibcode: 2012atnf.prop.5114M Altcode: We propose to perform the first phase observations of the enormous flare due to vast mass infall onto the Sgr A* black hole using the ATCA at 15, 7, and 3 mm bands in order to record the spectacular event as soon as possible after our detection of the increase in flux density of Sgr A* from the daily monitoring using the short-baseline VLBI in Japan. Title: Chromospheric Lyman-alpha spectro-polarimeter (CLASP) Authors: Kano, Ryouhei; Bando, Takamasa; Narukage, Noriyuki; Ishikawa, Ryoko; Tsuneta, Saku; Katsukawa, Yukio; Kubo, Masahito; Ishikawa, Shin-nosuke; Hara, Hirohisa; Shimizu, Toshifumi; Suematsu, Yoshinori; Ichimoto, Kiyoshi; Sakao, Taro; Goto, Motoshi; Kato, Yoshiaki; Imada, Shinsuke; Kobayashi, Ken; Holloway, Todd; Winebarger, Amy; Cirtain, Jonathan; De Pontieu, Bart; Casini, Roberto; Trujillo Bueno, Javier; Štepán, Jiří; Manso Sainz, Rafael; Belluzzi, Luca; Asensio Ramos, Andres; Auchère, Frédéric; Carlsson, Mats Bibcode: 2012SPIE.8443E..4FK Altcode: One of the biggest challenges in heliophysics is to decipher the magnetic structure of the solar chromosphere. The importance of measuring the chromospheric magnetic field is due to both the key role the chromosphere plays in energizing and structuring the outer solar atmosphere and the inability of extrapolation of photospheric fields to adequately describe this key boundary region. Over the last few years, significant progress has been made in the spectral line formation of UV lines as well as the MHD modeling of the solar atmosphere. It is found that the Hanle effect in the Lyman-alpha line (121.567 nm) is a most promising diagnostic tool for weaker magnetic fields in the chromosphere and transition region. Based on this groundbreaking research, we propose the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) to NASA as a sounding rocket experiment, for making the first measurement of the linear polarization produced by scattering processes and the Hanle effect in the Lyman-alpha line (121.567 nm), and making the first exploration of the magnetic field in the upper chromosphere and transition region of the Sun. The CLASP instrument consists of a Cassegrain telescope, a rotating 1/2-wave plate, a dual-beam spectrograph assembly with a grating working as a beam splitter, and an identical pair of reflective polarization analyzers each equipped with a CCD camera. We propose to launch CLASP in December 2014. Title: Oscillation Phenomena in the Disk around the Massive Black Hole Sagittarius A* Authors: Miyoshi, Makoto; Shen, Zhi-Qiang; Oyama, Tomoaki; Takahashi, Rohta; Kato, Yoshiaki Bibcode: 2011PASJ...63.1093M Altcode: We report the detection of radio QPOs with structure changes using the Very Long Baseline Array (VLBA) at 43 GHz. We found conspicuous patterned changes of the structure with P = 16.8±1.4, 22.2±1.4, 31.4±1.5, 56.4±6 min roughly in a 3:4:6:10 ratio. The first two periods show a rotating one-arm structure, while P = 31.4 min shows a rotating 3-arm structure, as if viewed edge-on. At the central 50 μas the P = 56.4 min period shows a double-amplitude variation of those in its surroundings. The spatial distributions of the oscillation periods suggest that the disk of Sgr A* is roughly edge-on, rotating around an axis with PA = -10°. Presumably, the observed VLBI images of Sgr A* at 43 GHz retain several features of the black hole accretion disk of Sgr A* in spite of being obscured and broadened by scattering of surrounding plasma. Title: Excitation of magneto-acoustic waves in network magnetic elements Authors: Kato, Yoshiaki; Steiner, Oskar; Steffen, Matthias; Suematsu, Yoshinori Bibcode: 2011IAUS..273..442K Altcode: From radiation magnetohydrodynamic (RMHD) simulations we track the temporal evolution of a vertical magnetic flux sheet embedded in a two-dimensional non-stationary atmosphere that reaches all the way from the upper convection zone to the low chromosphere. Examining its temporal behavior near the interface between the convection zone and the photosphere, we describe the excitation of propagating longitudinal waves within the magnetic element as a result of convective motion in its surroundings. Title: Excitation of Slow Modes in Network Magnetic Elements Through Magnetic Pumping Authors: Kato, Yoshiaki; Steiner, Oskar; Steffen, Matthias; Suematsu, Yoshinori Bibcode: 2011ApJ...730L..24K Altcode: 2011arXiv1102.5164K From radiation magnetohydrodynamic simulations of the solar atmosphere, we find a new mechanism for the excitation of longitudinal slow modes within magnetic flux concentrations. We find that the convective downdrafts in the immediate surroundings of magnetic elements are responsible for the excitation of slow modes. The coupling between the external downdraft and the plasma motion internal to the flux concentration is mediated by the inertial forces of the downdraft that act on the magnetic flux concentration. These forces, in conjunction with the downward movement, pump the internal atmosphere in the downward direction, which entails a fast downdraft in the photospheric and chromospheric layers of the magnetic element. Subsequent to the transient pumping phase, the atmosphere rebounds, causing a slow mode traveling along the magnetic flux concentration in the upward direction. It develops into a shock wave in chromospheric heights, possibly capable of producing some kind of dynamic fibril. We propose an observational detection of this process. Title: Theoretical Interpretation of X-ray Spectra from Active Galactic Nuclei and Low/Hard State of X-ray Binaries with an Accretion Disk-Corona Model Authors: Kawanaka, Norita; Kato, Yoshiaki; Mineshige, Shin Bibcode: 2010ecsa.conf..304K Altcode: No abstract at ADS Title: Global Radiation-Magnetohydrodynamic Simulations of Black-Hole Accretion Flow and Outflow: Unified Model of Three States Authors: Ohsuga, Ken; Mineshige, Shin; Mori, Masao; Kato, Yoshiaki Bibcode: 2009PASJ...61L...7O Altcode: 2009arXiv0903.5364O Black-hole accretion systems are known to possess several distinct modes (or spectral states), such as low/hard state, high/soft state, and so on. Since the dynamics of the corresponding flows is distinct, theoretical models were separately discussed for each state. We here propose a unified model based on our new, global, two-dimensional radiation-magnetohydrodynamic simulations. By controlling a density normalization we could for the first time reproduce three distinct modes of accretion flow and outflow with one numerical code. When the density is large (model A), a geometrically thick, very luminous disk forms, in which photon trapping takes place. When the density is moderate (model B), the accreting gas can effectively cool by emitting radiation, thus generating a thin disk, i.e., the soft-state disk. When the density is too low for radiative cooling to be important (model C), a disk becomes hot, thick, and faint; i.e., the hard-state disk. The magnetic energy is amplified within the disk up to about twice, 30%, and 20% of the gas energy in models A, B, and C, respectively. Notably, the disk outflows with helical magnetic fields, which are driven either by radiation pressure force or magnetic pressure force, are ubiquitous in any accretion modes. Finally, our simulations are consistent with the phenomenological alpha-viscosity prescription, that is, the disk viscosity is proportional to the pressure. Title: X-Ray Emissions from Three-Dimensional Magnetohydrodynamic Coronal Accretion Flows Authors: Kawanaka, Norita; Kato, Yoshiaki; Mineshige, Shin Bibcode: 2008PASJ...60..399K Altcode: 2008arXiv0801.4613K We calculated the radiation spectrum and its time variability of a black-hole accretion disk-corona system based on a three-dimensional magnetohydrodynamic (MHD) simulation. In explaining the spectral properties of active galactic nuclei, it is often assumed that they consist of a geometrically thin, optically thick disk and hot, optically thin corona surrounding the thin disk. As for a model of the corona, we adopted the simulation data of three-dimensional, non-radiative MHD accretion flows calculated by Y. Kato and coworkers, while for a thin disk we assumed a standard-type disk. We performed Monte-Carlo radiative transfer simulations of the corona, while taking into account the Compton scattering of soft photons from the thin disk by hot thermal electrons and coronal irradiation heating of the thin disk, which emits blackbody radiation. By adjusting the density parameter of the MHD coronal flow, we could produce emergent spectra that are consistent with those of typical Seyfert galaxies. Moreover, we found rapid time variability in the X-ray emission spectra, originating from a density fluctuation produced by a magnetorotational instability in the MHD corona. The features of reflection component including iron fluorescent line emission are also briefly discussed. Title: 3-D MHD Simulations of Astrophysical Jets Authors: Kato, Yoshiaki Bibcode: 2008APS..APR3HE002K Altcode: Jets and outflows are ubiquitous among the accretion process in a variety of astrophysical objects. Global three-dimensional (3-D) magnetohydrodynamic (MHD) simulations of accretion flows have revealed the generation of jets by the emergence of a magnetic tower. In other words, the magnetic interaction associated with stars and/or accretion disks is a promising universal mechanism of launching jets. However, photon spectra of accretion flows and jets in some microquasars display some serious problems. When spetrum is dominated by non-thermal emissions, a mildly relativistic steady jet is observed. On the other hand, when spectrum is dominated by thermal emissions, no jet is observed. Remarkably, during a transition from a non-thermal state to a thermal state, a ultra-relativistic transient jet is observed. Therefore, the radiation in a magnetized accretion flow is a key to understand the formation of jets. In this talk, we present 3-D MHD simulations of magnetic tower jets and also 3-D radiation transfer (RT) simulations of magnetic tower jets. The possible connection between the emergence of magnetic tower jets and the evolution of radiation properties will be discussed. Title: Magnetic-Tower Jet Solution for Launching Astrophysical Jets Authors: Kato, Yoshiaki Bibcode: 2007Ap&SS.307...11K Altcode: 2006Ap&SS.tmp..531K In spite of the large number of global three-dimensional (3-D) magnetohydrodynamic (MHD) simulations of accretion disks and astrophysical jets, which have been developed since 2000, the launching mechanisms of jets is somewhat controversial. Previous studies of jets have concentrated on the effect of the large-scale magnetic fields permeating accretion disks. However, the existence of such global magnetic fields is not evident in various astrophysical objects, and their origin is not well understood. Thus, we study the effect of small-scale magnetic fields confined within the accretion disk. We review our recent findings on the formation of jets in dynamo-active accretion disks by using 3-D MHD simulations. In our simulations, we found the emergence of accumulated azimuthal magnetic fields from the inner region of the disk (the so-called magnetic tower) and also the formation of a jet accelerated by the magnetic pressure of the tower. Our results indicate that the magnetic tower jet is one of the most promising mechanisms for launching jets from the magnetized accretion disk in various astrophysical objects. We will discuss the formation of cosmic jets in the context of the magnetic tower model. Title: Magnetized accretion flow, jets, and coronae Authors: Mineshige, Shin; Kato, Yoshiaki; Ohsuga, Ken; Kawanaka, Norita Bibcode: 2005AIPC..801..147M Altcode: Magnetic fields seem to play critical roles in accretion flow, jets, and coronae. We overview their roles in connection with observations. Special attentions will be paid on the spectral properties of magnetized flow and corona, and emergence of magnetic-tower jets from localized fields. Despite rapid progress in numerical simulations we are still in a state far from being complete in understanding. Outstanding issues are also presented. Title: Formation of magnetic-tower jets in magnetohydrodynamic accretion flows Authors: Kato, Yoshiaki Bibcode: 2005AstHe..98..525K Altcode: The previous study of astrophysical jets has been concentrated on the effects of large-scale magnetic fields permeating accretion disks. However, the existence of such global magnetic fields is not evident in many astrophysical objects. Instead, the magnetic fields, generated in the disks as a result of magneto-rotational instability, can create jets accelerated by the magnetic pressure of the magnetic-tower. We describe our attempt to explore the magnetic-tower jet solution as a unified model of astrophysical jets. Title: Spectral Properties of Three-dimensional Magnetohydrodynamic Accretion Flows Authors: Ohsuga, Ken; Kato, Yoshiaki; Mineshige, Shin Bibcode: 2005ApJ...627..782O Altcode: 2005astro.ph..3686O In spite of a large number of global three-dimensional MHD simulations of accretion flows and jets being made recently, their astrophysical relevance for realistic situations is not well known. In order to examine to what extent the simulated MHD flows can account for the observed SED of Sgr A*, for the first time we calculate the emergent spectra from three-dimensional MHD flows in a wide range of wavelengths (from radio to X-ray) by solving the three-dimensional radiative transfer equations. We use the simulation data by Kato and coworkers and perform Monte Carlo radiative transfer simulations, in which synchrotron emission/absorption, free-free emission/absorption, and Compton/inverse Compton scattering are taken into account. We assume two-temperature plasmas and calculate electron temperatures by solving the electron energy equation. Only thermal electrons are considered. It is found that the three-dimensional MHD flow generally overproduces X-rays by means of bremsstrahlung radiation from the regions at large radii. A flatter density profile, ρ~r-a with a<1, than that of the ADAF, ρ~r-3/2, is the main reason for this. If we restrict the size of the emission region to be as small as ~10rS, where rS is the Schwarzschild radius, the MHD model can reproduce the basic features of the observed SED of Sgr A* during its flaring state. Yet, the spectrum in the quiescent state remains to be understood. We discuss how to resolve this issue in the context of MHD flow models. Possibilities include modifications of the MHD flow structure by the inclusion of radiative cooling and/or significant contributions by nonthermal electrons. It is also possible that the present spectral results may be influenced by particular initial conditions. We also calculate the time-dependent spectral changes, finding that the fluxes fluctuate in a wide range of the frequency and the flux at each wavelength does not always vary coherently. Title: 2:3 Twin Quasi-Periodic Oscillations in Magnetohydrodynamic Accretion Flows Authors: Kato, Yoshiaki Bibcode: 2004PASJ...56..931K Altcode: 2004astro.ph..8018K We have studied the radial and vertical oscillations in three-dimensional magnetohydrodynamic (MHD) accretion flows around black holes. General-relativistic effects were taken into account by using a pseudo-Newtonian potential. We found that the structure of MHD flows is changed at 3.8rs ≤ r ≤ 6.3rs, and that two pairs of quasi-periodic oscillations (twin QPOs) are excited in that region. The time evolution of the power spectrum density (PSD) indicates that these twin QPOs are most likely to be produced by a resonance between the Keplerian frequency, νK, and the epicyclic frequency, νK. The PSD shows that the lower peak frequency, νl corresponds to, νK, while the upper peak frequency, νu, corresponds to νK + νκ. The ratio of two peak frequencies is close to 2 : 3. The results provide the first direct evidence for the excitation of resonant disk oscillation in MHD accretion flows. Title: XUV laser research at the Rutherford Appleton Laboratory Authors: Key, Michael H.; Rose, S. J.; Grande, Manuel; Tallents, Gregory J.; Ramsden, Stuart A.; Rogoyski, A.; Lewis, Ciaran L.; O'Neill, D. M.; Regan, C.; Evans, Brian L.; Al-Arab, Ali M.; Pert, Geoffrey J.; Henshaw, M.; Jaegle, Pierre; Carillon, Antoine; Klisnick, Annie; Jamelot, Gerard; Sureau, Alain; Guennou, M.; Kato, Yoshiaki; Yamanaka, Masanobu; Dido, H.; Tachi, T.; Nishimura, Hiroaki; Shiraga, H.; Herman, P.; Miura, E.; Takabe, Hideaki; McLean, Edgar A.; Lee, Tim Bibcode: 1989SPIE.1140...21K Altcode: No abstract at ADS