explanation      blue bibcodes open ADS page with paths to full text
Author name code: kato
ADS astronomy entries on 2022-09-14
=author:"Kato, Yoshiaki" 

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Title: Comments on "Imaging Reanalyses of EHT Data"
Authors: Miyoshi, Makoto; Kato, Yoshiaki; Makino, Jun
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.

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Title: Radiation Magnetohydrodynamic Simulations of sub-Eddington
    accretion flows in AGN
Authors: Igarashi, Taichi; Matsumoto, Yosuke; Matsumoto, Ryoji; Kato,
   Yoshiaki; Takahashi, Hiroyuki; Ohsuga, Ken
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.

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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
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.

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Title: Wakefield Acceleration in a Jet from a Neutrino-driven
    Accretion Flow around a Black Hole
Authors: Kato, Yoshiaki; Ebisuzaki, Toshikazu; Tajima, Toshiki
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 <SUB>⊙</SUB> s<SUP>-1</SUP> 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 10<SUP>20</SUP> eV.

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Title: X-ray laser development at the Institute of Laser Engineering,
    Osaka University with worldwide collaboration
Authors: Kato, Yoshiaki; Daido, Hiroyuki
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.

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Title: Wakefield Acceleration in a Jet from a Neutrino Driven
    Accretion Flow around a Black Hole
Authors: Kato, Yoshiaki; Ebisuzaki, Toshikazu; Tajima, Toshiki
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 &lt;= 10M⊙, such extreme accretions
  are investigated as a model of gamma-ray bursts (GRBs) as well as
  supernovae and hypernovae. Recently, Ebisuzaki &amp; Tajima 2019
  (ET19) have proposed a model of acceleration mechanism of charged
  particles to very high energies ~ 10<SUP>20</SUP> 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 L<SUB>wave</SUB> = Mc<SUP>2</SUP> / ?? √
  18α<SUP>2</SUP>β<SUP>3</SUP> and the that of neutrinos L<SUB>ν</SUB>
  = Mc<SUP>2</SUP> / 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.

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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
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 $&lt;$$ 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.

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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
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 (∼10<SUP>7-8</SUP> 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.

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Title: Chromospheric and Coronal Wave Generation in a Magnetic
    Flux Sheath
Authors: Kato, Yoshiaki; Steiner, Oskar; Hansteen, Viggo; Gudiksen,
   Boris; Wedemeyer, Sven; Carlsson, Mats
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.

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Title: The statistical properties of vortex flows in the solar
    atmosphere
Authors: Wedemeyer, Sven; Kato, Yoshiaki; Steiner, Oskar
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

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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
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&amp;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&amp;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&amp;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.

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Title: Saturation of Stellar Winds from Young Suns
Authors: Suzuki, Takeru K.; Imada, Shinsuke; Kataoka, Ryuho; Kato,
   Yoshiaki; Matsumoto, Takuma; Miyahara, Hiroko; Tsuneta, Saku
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 B<SUB>r,</SUB><SUB>0</SUB>
  f<SUB>0</SUB>, where B<SUB>r,</SUB><SUB>0</SUB> and f<SUB>0</SUB>
  are the magnetic field strength and the filling factor of open flux
  tubes at the photosphere. If B<SUB>r,</SUB><SUB>0</SUB> f<SUB>0</SUB>
  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<SUP>-1.23</SUP>, of our simulations, combining
  with an observed time evolution of X-ray flux from Sun-like stars,
  which are shallower than dot;{M} ∝ t<SUP>-2.33±0.55</SUP> in Wood
  et al. (2005).

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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
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.

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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
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.

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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
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.

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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
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.

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Title: Oscillation Phenomena in the Disk around the Massive Black
    Hole Sagittarius A<SUP>*</SUP>
Authors: Miyoshi, Makoto; Shen, Zhi-Qiang; Oyama, Tomoaki; Takahashi,
   Rohta; Kato, Yoshiaki
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.

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Title: Excitation of magneto-acoustic waves in network magnetic
    elements
Authors: Kato, Yoshiaki; Steiner, Oskar; Steffen, Matthias; Suematsu,
   Yoshinori
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.

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Title: Excitation of Slow Modes in Network Magnetic Elements Through
    Magnetic Pumping
Authors: Kato, Yoshiaki; Steiner, Oskar; Steffen, Matthias; Suematsu,
   Yoshinori
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.

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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
2010ecsa.conf..304K    Altcode:
  No abstract at ADS

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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
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.

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Title: X-Ray Emissions from Three-Dimensional Magnetohydrodynamic
    Coronal Accretion Flows
Authors: Kawanaka, Norita; Kato, Yoshiaki; Mineshige, Shin
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.

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Title: 3-D MHD Simulations of Astrophysical Jets
Authors: Kato, Yoshiaki
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.

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Title: Magnetic-Tower Jet Solution for Launching Astrophysical Jets
Authors: Kato, Yoshiaki
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.

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Title: Magnetized accretion flow, jets, and coronae
Authors: Mineshige, Shin; Kato, Yoshiaki; Ohsuga, Ken; Kawanaka, Norita
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.

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Title: Formation of magnetic-tower jets in magnetohydrodynamic
    accretion flows
Authors: Kato, Yoshiaki
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.

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Title: Spectral Properties of Three-dimensional Magnetohydrodynamic
    Accretion Flows
Authors: Ohsuga, Ken; Kato, Yoshiaki; Mineshige, Shin
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<SUP>-a</SUP> with a&lt;1, than that of the
  ADAF, ρ~r<SUP>-3/2</SUP>, is the main reason for this. If we restrict
  the size of the emission region to be as small as ~10r<SUB>S</SUB>,
  where r<SUB>S</SUB> 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.

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Title: 2:3 Twin Quasi-Periodic Oscillations in Magnetohydrodynamic
    Accretion Flows
Authors: Kato, Yoshiaki
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 3.8r<SUB>s</SUB> ≤ r ≤ 6.3r<SUB>s</SUB>, 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, ν<SUB>K</SUB>, and the
  epicyclic frequency, ν<SUB>K</SUB>. The PSD shows that the lower peak
  frequency, ν<SUB>l</SUB> corresponds to, ν<SUB>K</SUB>, while the
  upper peak frequency, ν<SUB>u</SUB>, corresponds to ν<SUB>K</SUB>
  + ν<SUB>κ</SUB>. 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.

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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
1989SPIE.1140...21K    Altcode:
  No abstract at ADS