647 research outputs found
Orbital Parameters for the Black Hole Binary XTE J1650-500
(Shortened) We present R-band photometry of the X-ray transient and candidate
black hole binary XTE J1650-500 obtained between 2003 May and August with the
6.5m Clay Telescope. A timing analysis of these data reveals a photometric
period of 0.3205 +/- 0.0007 days (i.e. 7.63 hr) with a possible alias at 0.3785
days (9.12 hr). Our photometry completely rules out the previously published
spectroscopic period of 0.212 days (5.09 hr). Consequently, we reanalyzed the
15 archival ESO/VLT spectra (obtained 2002 June by Sanchez-Fernandez et al.)
that were the basis of the previously published spectroscopic period. We used a
``restframe search'' technique that is well suited for cases when the
signal-to-noise ratio of individual spectra is low. The results confirmed the
photometric period of 0.3205 days, and rule out the alias period near 0.38
days. The best value for the velocity semiamplitude of the companion star is
K_2 = 435 +/- 30 km/sec, and the corresponding optical mass function is f(M) =
2.73 +/- 0.56 solar masses. The amplitude of the phased R-band light curve is
0.2 magnitudes, which gives a lower limit to the inclination of 50 +/- 3
degrees in the limiting case of no contribution to the R-band light curve from
the accretion disk. If the mass ratio of XTE J1650-500 is similar to the mass
ratios of other black hole binaries like A0620-00 or GRS 1124-683 (e.g. Q >~
10), then our lower limit to the inclination gives an upper limit to the mass
of the black hole in XTE J1650-500 of M_1 <~ 7.3 solar masses. However, the
mass can be considerably lower if the R-band flux is dominated by the accretion
disk. For example, if the accretion disk does contribute 80% of the flux, as
our preliminary results suggest, then the black hole mass would be only about 4
solar masses.Comment: Accepted to ApJ. 15 pages, 5 figures (two of degraded quality).
Revised after referee's Comments, conclusions are unchange
A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass
Using the Very Long Baseline Array, we have measured a trigonometric parallax
for the micro quasar GRS 1915+105, which contains a black hole and a K-giant
companion. This yields a direct distance estimate of 8.6 (+2.0,-1.6) kpc and a
revised estimate for the mass of the black hole of 12.4 (+2.0,-1.8) Msun. GRS
1915+105 is at about the same distance as some HII regions and water masers
associated with high-mass star formation in the Sagittarius spiral arm of the
Galaxy. The absolute proper motion of GRS 1915+105 is -3.19 +/- 0.03 mas/y and
-6.24 +/- 0.05 mas/y toward the east and north, respectively, which corresponds
to a modest peculiar speed of 22 +/-24 km/s at the parallax distance,
suggesting that the binary did not receive a large velocity kick when the black
hole formed. On one observational epoch, GRS 1915+105 displayed superluminal
motion along the direction of its approaching jet. Considering previous
observations of jet motions, the jet in GRS 1915+105 can be modeled with a jet
inclination to the line of sight of 60 +/- 5 deg and a variable flow speed
between 0.65c and 0.81c, which possibly indicates deceleration of the jet at
distances from the black hole >2000 AU. Finally, using our measurements of
distance and estimates of black hole mass and inclination, we provisionally
confirm our earlier result that the black hole is spinning very rapidly.Comment: 20 pages; 2 tables; 6 figure
Complete RXTE Spectral Observations of the Black Hole X-ray Nova XTE J1550-564
We report on the X-ray spectral behavior of the exceptionally bright X-ray
nova XTE J1550-564 during its 1998-99 outburst. Our study is based on 209
pointed observations using the PCA and HEXTE instruments onboard the Rossi
X-ray Timing Explorer spanning 250 days and covering the entire double-peaked
eruption that occurred from 1998 September until 1999 May. The spectra are fit
to a model including multicolor blackbody disk and power-law components. The
source is observed in the very high and high/soft outburst states of black hole
X-ray novae. During the very high state, when the power-law component dominated
the spectrum, the inner disk radius is observed to vary by more than an order
of magnitude; the radius decreased by a factor of 16 in one day during a 6.8
Crab flare. If the larger of these observed radii is taken to be the last
stable orbit, then the smaller observed radius would imply that the inner edge
of the disk is inside the event horizon! However, we conclude that the apparent
variations of the inner disk radius observed during periods of increased
power-law emission are probably caused by the failure of the multicolor
disk/power-law model; the actual physical radius of the inner disk may remain
fairly constant. This interpretation is supported by the fact that the observed
inner disk radius remains approximately constant over 120 days in the high
state, when the power-law component is weak, even though the disk flux and
total flux vary by an order of magnitude. The mass of the black hole inferred
by equating the approximately constant inner disk radius observed in the
high/soft state with the last stable orbit for a Schwarzschild black hole is
M_BH = 7.4 M_sun (D/6 kpc) (cos i)^{-1/2}.Comment: Submitted to ApJ, 20 pages including 6 figures + 4 large table
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
Use of Gas Electron Multiplier (GEM) Detectors for an Advanced X-ray Monitor
We describe a concept for a NASA SMEX Mission in which Gas Electron
Multiplier (GEM) detectors, developed at CERN, are adapted for use in X-ray
astronomy. These detectors can be used to obtain moderately large detector area
and two-dimensional photon positions with sub mm accuracy in the range of 1.5
to 15 keV. We describe an application of GEMs with xenon gas, coded mask
cameras, and simple circuits for measuring event positions and for
anticoincidence rejection of particle events. The cameras are arranged to cover
most of the celestial sphere, providing high sensitivity and throughput for a
wide variety of cosmic explosions. At longer timescales, persistent X-ray
sources would be monitored with unprecedented levels of coverage. The
sensitivity to faint X-ray sources on a one-day timescale would be improved by
a factor of 6 over the capability of the RXTE All Sky Monitor.Comment: 10 pages, 5 figs., in X-Ray and Gamma Ray Instrumentation for
Astronomy XI, SPIE conference, San Diego, Aug. 200
X-ray Properties of Black-Hole Binaries
We review the properties and behavior X-ray binaries that contain an
accreting black hole. The larger majority of such systems are X-ray transients,
and many of them were observed in daily pointings with RXTE throughout the
course of their outbursts. The complex evolution of these sources is described
in terms of common behavior patterns illustrated with comprehensive overview
diagrams for six selected systems. Central to this comparison are three X-ray
states of accretion, which are reviewed and defined quantitatively. Each state
yields phenomena that arise in strong gravitational fields. We sketch a
scenario for the potential impact of black hole observations on physics and
discuss a current frontier topic: the measurement of black hole spin.Comment: 39 pages, 12 figures, ARAA, vol. 44, in pres
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
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