32 research outputs found
X-ray Transients Monitored by the All-Sky Monitor on RXTE: A Tabulation
We present a tabulation of 46 transient x-ray sources monitored with the
All-Sky Monitor (ASM) on the Rossi X-ray Timing Explorer (RXTE). They fall into
four broad categories: short (~d), intermediate, and long (>500 d) duration of
outbursts, and long period binary systems that flare up at periastron (e.g., Be
systems). The mixture of outburst/quiescent cycles and low-level persistent
emission in a few systems could indicate conditions are near the limit for
stable mass flow in the accretion disk. The two short-time-scale systems, CI
Cam and V4641 Sgr, are within 1 kpc of the sun, and hence many more such
systems may await discovery.Comment: 18 pages, 2 figures, Submitted for publication in "X-ray Astronomy
'99; Stellar Endpoints, AGN and the Diffuse Background", Ed: G.Malaguti,
G.Palumbo, and N.White, pub. Gordon and Breach (v.2: Additional references
added, erroneous figure replaced
The optical identification and spectral analysis of celestial X-ray sources
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985.Microfiche copy available in Archives and Science.Vita.Bibliography: leaves 152-162.by Ronald Alan Remillard.Ph.D
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
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
RADIATION PRESSURE AND MASS EJECTION IN ρ-LIKE STATES OF GRS 1915+105
We present a unifying scenario to address the physical origin of the diversity of X-ray light curves within the ρ variability class of the microquasar GRS 1915+105. This "heartbeat" state is characterized by a bright flare that recurs every ~50-100 s, but the profile and duration of the flares vary significantly from observation to observation. Based on a comprehensive, phase-resolved study of heartbeats in the Rossi X-ray Timing Explorer archive, we demonstrate that very different X-ray light curves do not require origins in different accretion processes. Indeed, our detailed comparison of the phase-resolved spectra of a double-peaked oscillation and a single-peaked oscillation shows that different cycles can have basically similar X-ray spectral evolution. We argue that all heartbeat oscillations can be understood as the result of a combination of a thermal-viscous radiation pressure instability, a local Eddington limit in the disk, and a sudden, radiation-pressure-driven evaporation or ejection event in the inner accretion disk. This ejection appears to be a universal, fundamental part of the ρ state, and is largely responsible for a hard X-ray pulse seen in the light curve of all cycles. We suggest that the detailed shape of oscillations in the mass accretion rate through the disk is responsible for the phenomenological differences between different ρ-type light curves, and we discuss how future time-dependent simulations of disk instabilities may provide new insights into the role of radiation pressure in the accretion flow.Chandra X-ray Center (U.S.) (Grant GO7-8044X)Harvard University. Graduate School of Arts and Science
Observations of Gamma-ray Bursts with the Rossi X-ray Timing Explorer
The role of the Rossi X-ray Timing Explorer (RXTE) in the study of Gamma-ray
Bursts (GRBs) is reviewed. Through April 2001, the All-Sky Monitor (ASM) and
the Proportional Counter Array (PCA) instruments have detected 30 GRBs. In 16
cases, an early celestial position was released to the community, sometimes in
conjunction with IPN results. The subsequent optical and radio searches led to
the detection of 5 x-ray afterglows, to at least 6 optical or radio afterglows,
to 3 of the 17 secure redshifts known at this writing, and to 2 other likely
redshifts. The decay curves of early x-ray afterglows have been measured. The
rapid determination of the location of GRB 970828 and the absence of optical
afterglow at that position gave one of the first indications that GRBs occur in
star-forming regions (Groot et al. 1998, ApJ 493, L27). The location of GRB
000301C led to the determination of a break in the optical decay rate (Rhoads
and Fruchter 2001, ApJ 546, 117) which is evidence for a jet, and to
variability in the optical light curve that could represent gravitational
lensing (Garnavich, Loeb, and Stanek 2000, ApJ 544, L11). X-ray light curves of
GRB from the ASM in conjunction with gamma-ray light curves exhibit striking
differences in different bands and may reveal the commencement of the x-ray
afterglow (Smith et al. 2001, ApJ submitted, astroph 0103357).Comment: Accepted for Proceeding Proceedings Of The Joint CNR/ESO Meeting,
"Gamma-Ray Bursts in the Afterglow Era: 2nd Workshop", Rome, Italy, October
17-20, 2000, eds. F. Frontera, E. Costa, J. Hjorth, in "ESO Astrophysics
Symposia" series, Springer Verlag., 8 pages, 4 figure