91 research outputs found
X-Ray Spectra of the Narrow-Line Seyfert 1 Galaxy Ton S180 in Comparison with Galactic Black Holes
An analysis was made of 0.3-15 keV X-ray spectra of a Narrow-Line Seyfert 1
Galaxy, Ton S180, using archival data from ASCA, RXTE, and XMM-Newton. At
energies above 2.5 keV, a power-law with a photon index of ~ 2.3 successfully
and consistently reproduced the spectra from all of these observatories.
Assuming this power-law component to extend toward lower energies, a soft
excess, which is one of the most remarkable features of Narrow-Line Seyfert 1
Galaxies, is explained by another power-law multiplied by a thermal cutoff at ~
0.4 keV. Some similarities have been observed between this object and Galactic
black hole binaries in very high state, the latter being realized under high
accretion rates. Attempts have been made to interpret the soft excess in terms
of Comptonization of the disk photons by an electron cloud surrounding the
accretion disk, like BHBs in a very high state.Comment: 7 pages, 7 figure
Recurrent Outbursts and Jet Ejections Expected in Swift J1644+57: Limit-Cycle Activities in a Supermassive Black Hole
The tidal disruption event by a supermassive black hole in Swift J1644+57 can
trigger limit-cycle oscillations between a supercritically accreting X-ray
bright state and a subcritically accreting X-ray dim state. Time evolution of
the debris gas around a black hole with mass M=10^{6} {\MO} is studied by
performing axisymmetric, two-dimensional radiation hydrodynamic simulations. We
assumed the -prescription of viscosity, in which the viscous stress is
proportional to the total pressure. The mass supply rate from the outer
boundary is assumed to be , where
is the Eddington luminosity, and is the light speed. Since
the mass accretion rate decreases inward by outflows driven by radiation
pressure, the state transition from a supercritically accreting slim disk state
to a subcritically accreting Shakura-Sunyaev disk starts from the inner disk
and propagates outward in a timescale of a day. The sudden drop of the X-ray
flux observed in Swift J1644+57 in August 2012 can be explained by this
transition. As long as exceeds the threshold for the
existence of a radiation pressure dominant disk, accumulation of the accreting
gas in the subcritically accreting region triggers the transition from a gas
pressure dominant Shakura-Sunyaev disk to a slim disk. This transition takes
place at days after the X-ray darkening. We expect
that if , X-ray emission with luminosity and jet ejection will revive in Swift J1644+57 in
2013--2014.Comment: 6 pages, 4 figures, accepted for publication in PASJ Letter
Slow and Fast Transitions in the Rising Phase of Outbursts from NS-LMXB transients, AqlX-1 and 4U1608-52
We analyzed the initial rising behaviors of X-ray outbursts from two
transient low-mass X-ray binaries (LMXBs) containing a neutron-star (NS), Aql
X-1 and 4U 1608-52, which are continuously being monitored by MAXI/GSC in 2--20
keV, RXTE/ASM in 2--10 keV, and Swift/BAT in 15--50 keV. We found that the
observed ten outbursts are classified into two types by the patterns of the
relative intensity evolutions in the two energy bands below/above 15 keV. One
type behaves as the 15--50 keV intensity achieves the maximum during the
initial hard-state period and drops greatly at the hard-to-soft state
transition. On the other hand, the other type does as both the 2--15 keV and
the 15--50 keV intensities achieve the maximums after the transition. The
former have the longer initial hard-state ( 9 d) than the latter's
(\ltsim5 d). Therefore, we named them as slow-type (S-type) and fast-type
(F-type), respectively. These two types also show the differences in the
luminosity at the hard-to-soft state transition as well as in the average
luminosity before the outburst started, where the S-type are higher than the
F-type in the both. These results suggest that the X-ray radiation during the
pre-outburst period, which heats up the accretion disk and delays the disk
transition (i.e., from a geometrically thick disk to a thin one), would
determine whether the following outburst becomes S-type or F-type. The
luminosity when the hard-to-soft state transition occurs is higher than erg s in the S-type, which corresponds to 4% of the
Eddington luminosity for a 1.4 \Mo NS.Comment: 14 pages, 10 figures; Publications of the Astronomical Society of
Japan, 201
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