12,003 research outputs found
X-ray outbursts of low-mass X-ray binary transients observed in the RXTE era
We have performed a statistical study of the properties of 110 bright X-ray
outbursts in 36 low-mass X-ray binary transients (LMXBTs) seen with the All-Sky
Monitor (2--12 keV) on board the {\it Rossi X-ray Timing Explorer} ({\it RXTE})
in 1996--2011. We have measured a number of outburst properties, including peak
X-ray luminosity, rate of change of luminosity on a daily timescale,
-folding rise and decay timescales, outburst duration, and total radiated
energy. We found that the average properties such as peak X-ray luminosity,
rise and decay timescales, outburst duration, and total radiated energy of
black hole LMXBTs, are at least two times larger than those of neutron star
LMXBTs, implying that the measurements of these properties may provide
preliminary clues as to the nature of the compact object of a newly discovered
LMXBT. We also found that the outburst peak X-ray luminosity is correlated with
the rate of change of X-ray luminosity in both the rise and the decay phases,
which is consistent with our previous studies. Positive correlations between
total radiated energy and peak X-ray luminosity, and between total radiated
energy and the -folding rise or decay timescale, are also found in the
outbursts. These correlations suggest that the mass stored in the disk before
an outburst is the primary initial condition that sets up the outburst
properties seen later. We also found that the outbursts of two transient
stellar-mass ULXs in M31 also roughly follow the correlations, which indicate
that the same outburst mechanism works for the brighter outbursts of these two
sources in M31 that reached the Eddington luminosity.Comment: Accepted to Ap
A decades-long fast-rise-exponential-decay flare in low-luminosity AGN NGC 7213
We analysed the four-decades-long X-ray light curve of the low-luminosity
active galactic nucleus (LLAGN) NGC 7213 and discovered a
fast-rise-exponential-decay (FRED) pattern, i.e. the X-ray luminosity increased
by a factor of within 200d, and then decreased exponentially with
an -folding time d ( yr). For the theoretical
understanding of the observations, we examined three variability models
proposed in the literature: the thermal-viscous disc instability model, the
radiation pressure instability model, and the tidal disruption event (TDE)
model. We find that a delayed tidal disruption of a main-sequence star is most
favourable; either the thermal-viscous disk instability model or radiation
pressure instability model fails to explain some key properties observed, thus
we argue them unlikely.Comment: Accepted for publication in MNRAS, updated version after proof
correction
Microscopic structures and thermal stability of black holes conformally coupled to scalar fields in five dimensions
Completely from the thermodynamic point of view, we explore the microscopic
character of a hairy black hole of Einstein's theory conformally coupled to a
scalar field in five dimensions by means of the Ruppeiner thermodynamic
geometry. We demonstrate that the scalar hairy black hole has rich microscopic
structures in different parameter spaces. Moreover, we analyze the thermal
stability of this black hole in detail.Comment: v1: 15 pages, 1 figure; v2: 19 pages, clarifications and references
added; v3: clarifications and references added; v4: 21 pages, clarifications
added; v5: minor clarifications and one reference added, final version to
appear in Nuclear Physics
Hawking Radiation of Five-dimensional Charged Black Holes with Scalar Fields
We investigate the Hawking radiation cascade from the five-dimensional
charged black hole with a scalar field coupled to higher-order Euler densities
in a conformally invariant manner. We give the semi-analytic calculation of
greybody factors for the Hawking radiation. Our analysis shows that the Hawking
radiation cascade from this five-dimensional black hole is extremely sparse.
The charge enhances the sparsity of the Hawking radiation, while the
conformally coupled scalar field reduces this sparsity.Comment: v1: 11 pages, 2 figures, 2 tables; v2: 12 pages, references and
clarifications added, final version to appear in Phys. Lett.
- β¦