757 research outputs found
RXTE Spectral Observations of the 1996-97 Outburst of the Microquasar GRO J1655-40
Excellent coverage of the entire 16-month 1996-97 outburst cycle of GRO
J1655-40 was provided by RXTE. We present a full spectral analysis of these
data, which includes 52 PCA spectra from 2.5-20 keV and HEXTE spectra above 20
keV. We also include a nearly continuous ASM light curve with several intensity
measurements per day. The data are interpreted in the context of the multicolor
blackbody disk/power-law model. The source is observed in the very high,
high/soft, and low/hard outburst states. During the very high state, the source
exhibits intense hard flares on time scales of hours to days which are
correlated with changes in both the fitted temperature and radius of the inner
accretion disk. During the high/soft state, the spectrum is dominated by the
soft thermal emission from the accretion disk with spectral parameters that
suggest approximately constant inner disk radius and temperature. We find that
a tight relationship exists between the observed inner radius of the disk and
the flux in the power-law component. During intense hard flares, the inner disk
radius is observed to decrease by as much as a factor of three on a time scale
of days. The apparent decrease of the inner disk radius observed during the
flares may be due to the failure of the multicolor disk model caused by a
steepening of the radial temperature profile in the disk coupled with increased
spectral hardening and not physical changes of the inner disk radius. Assuming
that our spectral model is valid during periods of weak power-law emission, our
most likely value for the inner disk radius implies a* < 0.7. Such a low value
for the black hole angular momentum is inconsistent with the relativistic frame
dragging and the `diskoseismic' models as interpretations for the 300 Hz X-ray
QPO seen during some of these RXTE observations.Comment: 34 pages including 9 figures and 3 tables. Accepted for publication
in the Astrophysical Journal. Our interpretation of the data and the main
conclusions have been significantly revise
The influence of the metabolic syndrome on 24-year mortality among middle-aged men in the multiple risk factor intervention trial (MRFIT)
The Low-Spin Black Hole in LMC X-3
Building upon a new dynamical model for the X-ray binary LMC X-3, we measure
the spin of its black hole primary via the continuum-fitting method. We
consider over one thousand thermal-state RXTE X-ray spectra of LMC X-3. Using a
large subset of these spectra, we constrain the spin parameter of the black
hole to be spin = 0.21(+0.18,-0.22), 90% confidence. Our estimate of the
uncertainty in spin takes into account a wide range of systematic errors. We
discuss evidence for a correlation between a black hole's spin and the
complexity of its X-ray spectrum.Comment: Submitted to ApJL, 5 pages emulateapj, 2 figures and 1 tabl
The Mass of the Black Hole in Cygnus X-1
Cygnus X-1 is a binary star system that is comprised of a black hole and a
massive giant companion star in a tight orbit. Building on our accurate
distance measurement reported in the preceding paper, we first determine the
radius of the companion star, thereby constraining the scale of the binary
system. To obtain a full dynamical model of the binary, we use an extensive
collection of optical photometric and spectroscopic data taken from the
literature. By using all of the available observational constraints, we show
that the orbit is slightly eccentric (both the radial velocity and photometric
data independently confirm this result) and that the companion star rotates
roughly 1.4 times its pseudosynchronous value. We find a black hole mass of M
=14.8\pm1.0 M_{\sun}, a companion mass of M_{opt}=19.2\pm1.9 M_{\sun}, and the
angle of inclination of the orbital plane to our line of sight of i=27.1\pm0.8
deg.Comment: Paper II of three papers on Cygnus X-1; 27 pages including 5 figures
and 3 tables, ApJ in pres
Modeling the Optical-X-ray Accretion Lag in LMC X-3: Insights Into Black-Hole Accretion Physics
The X-ray persistence and characteristically soft spectrum of the black hole
X-ray binary LMC X-3 make this source a touchstone for penetrating studies of
accretion physics. We analyze a rich, 10-year collection of optical/infrared
(OIR) time-series data in conjunction with all available contemporaneous X-ray
data collected by the ASM and PCA detectors aboard the Rossi X-ray Timing
Explorer. A cross-correlation analysis reveals an X-ray lag of ~2 weeks.
Motivated by this result, we develop a model that reproduces the complex OIR
light curves of LMC X-3. The model is comprised of three components of
emission: stellar light; accretion luminosity from the outer disk inferred from
the time-lagged X-ray emission; and light from the X-ray-heated star and outer
disk. Using the model, we filter a strong noise component out of the
ellipsoidal light curves and derive an improved orbital period for the system.
Concerning accretion physics, we find that the local viscous timescale in the
disk increases with the local mass accretion rate; this in turn implies that
the viscosity parameter alpha decreases with increasing luminosity. Finally, we
find that X-ray heating is a strong function of X-ray luminosity below ~50% of
the Eddington limit, while above this limit X-ray heating is heavily
suppressed. We ascribe this behavior to the strong dependence of the flaring in
the disk upon X-ray luminosity, concluding that for luminosities above ~50% of
Eddington, the star lies fully in the shadow of the disk.Comment: Accepted in ApJ (12 pages long in emulateapj format
The X-ray Outburst of H1743-322: High-Frequency QPOs with a 3:2 Frequency Ratio
We observed the 2003 X-ray outburst of H1743-322 in a series of 130 pointed
observation with RXTE. We searched individual observations for high-frequency
QPOs (HFQPOs) and found only weak or marginal detections near 240 and 160 Hz.
We next grouped the observations in several different ways and computed the
average power-density spectra (PDS) in a search for further evidence of HFQPOs.
This effort yielded two significant results for those observations defined by
the presence of low-frequency QPOs (0.1-20 Hz) and an absence of
``band-limited'' power continua: (1) The 9 time intervals with the highest 7-35
keV count rates yielded an average PDS with a QPO at Hz. (; 3--35 keV); and (2) a second group with lower 7-35 keV count rates (26
intervals) produced an average PDS with a QPO at Hz (;
7--35 keV). The ratio of these two frequencies is . This finding
is consistent with results obtained for three other black hole systems that
exhibit commensurate HFQPOs in a 3:2 ratio. Furthermore, the occurrence of
H1743-322's slower HFQPO at times of higher X-ray luminosity closely resembles
the behavior of XTE J1550-564 and GRO J1655-40. We discuss our results in terms
of a resonance model that invokes frequencies set by general relativity for
orbital motions near a black-hole event horizon.Comment: 12 pages, 3 figures, submitted to Ap
Evidence for Harmonic Relationships in the High Frequency QPOs of XTE J1550-564 and GRO J1655-40
We continue to investigate the X-ray timing and spectral properties of the
black hole binary, XTE J1550-564. For three different groups of observations,
we show evidence that two high-frequency QPOs (HFQPOs) occur simultaneously
near 184 and 276 Hz. In one group, there is also evidence of a broad feature at
92 Hz. In each case, we can model the QPO profiles while assuming that the
central frequencies are related as integral harmonics of a single frequency. We
next investigate the X-ray energy spectra, and we find a systematic increase in
the strength of the power-law component as the stronger of the two HFQPOs
shifts from 276 to 184 Hz. A strikingly similar result is seen for GRO J1655-40
when the stronger HFQPO shifts from 450 to 300 Hz. The fundamental HFQPO
frequencies for the two X-ray sources scale inversely with black hole mass,
which is consistent with the hypotheses that these HFQPOs represent some
oscillation rooted in general relativity (GR) and that the two black holes have
similar values of the dimensionless spin parameter. We discuss physical
mechanisms that may explain these HFQPOs. In particular, a resonance between
the orbital and radial coordinate frequencies in the innner accretion disk, as
proposed by Abramowicz & Kluzniak, would imply moderate values for the
dimensionless spin parameter (0.1 < a < 0.6) for both black holes.Comment: 31 pages, including 9 figures and 1 Table; submitted to The Ap
Confirmation Via the Continuum-Fitting Method that the Spin of the Black Hole in Cygnus X-1 is Extreme
In Gou et al. (2011), we reported that the black hole primary in the X-ray
binary Cygnus X-1 is a near-extreme Kerr black hole with a spin parameter
a*>0.95(3{\sigma}). We confirm this result while setting a new and more
stringent limit: a*>0.983 at the 3{\sigma}(99.7%) level of confidence. The
earlier work, which was based on an analysis of all three useful spectra that
were then available, was possibly biased by the presence in these spectra of a
relatively strong Compton power-law component: The fraction of the thermal seed
photons scattered into the power law was f_s=23-31%, while the upper limit for
reliable application of the continuum-fitting method is f_s<25%. We have
subsequently obtained six additional spectra of Cygnus X-1 suitable for the
measurement of spin. Five of these spectra are of high quality with f_s in the
range 10% to 19%, a regime where the continuum-fitting method has been shown to
deliver reliable results. Individually, the six spectra give lower limits on
the spin parameter that range from a*>0.95 to a*>0.98, allowing us to
conservatively conclude that the spin of the black hole is a*>0.983
(3{\sigma}).Comment: 14 pages in emulated ApJ format, including 6 figures and 4 tables,
ApJ in press. Discussion on the pileup effect to our spin measurement is
added, including a subsection and a new figure, to reflect the referee's
comments; the conclusions are unchange
- …