5,449 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 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
Perception of concept and practice of social power in development interventions in Malawi
The study examined research participants’ perception of social power in intervention programmes in Malawi. Two districts and four villages with active participation in the intervention programmes were purposively selected. Focus group participants were purposively identified, while the snow balling procedure was employed to select key informants. A total of 375 participants consisting of 219 men and 156 women (to better explore the viewpoints of men from those of women) were drawn from the two study locations. Data were analysed by content analysis. The results showed that >98% of participants stated that power meant the ‘capacity of a social actor to influence decisions and secure compliance of other social actors. Less than 98% also perceived ‘power’ as the leadership ability of a social actor but few participants with high level of power shared this construct. Further analysis informed that power was perceived as the act of guiding fellow social actors to plan and implement activities serving common interest while another 50% of respondents perceived power as a mere potential ability to influence. Statistics however showed only 3.7% of relatively powerful social actors from agricultural extension workers and 1.3 % of sexual and reproductive health interventionists shared power as potential ability to influence way of thinking and doing. Therefore, stakeholders of development intervention should recognize experienced social actors and traditions as power indicators since these will enhance effective extension policy process aimed at development intervention among rural populace
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
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