Recent Research Activities
Black Hole Accretion
It is almost established
that optically thin advection-dominated accretion flow (ADAF)
is responsible for hard-X - gamma-ray emission from black-hole
objects. The ADAF is characterized by low density and high temperature,
thereby emissivity being low. Thus, librated energy of accreting
gas is carried by accreting gas without being radiated. We have
calculated a two-temperature disk and its spectrum.
- Kato, S., Fukue, J., & Mineshige,
Black-Hole Accretion Disks, Kyoto University Press, 1998.
- Manmoto, T., Mineshige, S., &
Spectrum of Optically Thin Advection-Dominated Accretion Flow
around a Black Hole: Application to Sagittarius A*, ApJ 489,
Transition of Black-Hole Candidates
Stellar-mass black-hole candidates
are known to oscillate between the hard (low) and soft (high)
spectral states. The former type of the disk can well be described
by the standard disk model, whereas the latter is represented
by the optically thin ADAF. We have succeeded in calculating such
a state transition by time-dependent disk evolutionary simulations.
- Takeuchi, M. & Mineshige, S.
Model for Spectral Transitions in Galactic Black-Hole Sources,
ApJ 505, L19, 1998.
black-hole objects (close binary systems and galactic nuclei)
is known to exhibit apparently random (1/f) fluctuations. Postulating
their origin being related to magnetic-field dissipation via magnetic
reconnection, we could reproduce the basic fluctuation properties
by cellular-automaton simulations based on the notion of self-organized
criticality (SOC) and also by three-dimensional MHD disk simulations.
- Kawaguchi, T., Mineshige, S., Umemura,
M., & Turner, E.L.
Optical Variability from Active Galactic Nuclei: Starbursts or
Disk Instabilities?, ApJ 504, 671, 1998.
Central Structure by Microlensing
of Q2237+0305(Einstein Cross) are results of gravitational lensing
of a distant quasar by a nearby galaxy. If stars in the lensing
galaxy passes just in front of an image of the quasar center,
radiation from the vicinity of a black hole can be selectively
amplified. Observations are scheduled with ground-based telescopes,
HST, AXAF, which will resolve the quasar central structure on
length scales down to several AUs.
Shin MINESHIGE <email@example.com>
- Yonehara, A., Mineshige, S., Manmoto,
T., Fukue, J., Umemura, M., & Turner, E.L.
An X-Ray Microlens Test of AU-Scale Disk Structure in Q2237+0305,
ApJ 501, L41, 1998; Erratum 511, L65, 1999.
- Mineshige, S., & Yonehara,
Gravitational Microlens Mapping of a Quasar Accretion Disk, PASJ
51, in press.