2,380 research outputs found
Observations of the X-ray Nova GRO~J0422+32: II: Optical Spectra Approaching Quiescence
We present results obtained from a series of 5~\AA\ resolution spectra of the
X-ray Nova GRO~J0422+32 obtained in 1993~October, when the system was
approximately 2 magnitudes above quiescence, with . The data
were obtained in an effort to measure the orbital radial velocity curve of the
secondary, but detection of the narrow photospheric absorption lines needed to
do this proved elusive. Instead we found wide absorption bands reminiscent of
M~star photospheric features. The parameters determined by fitting accretion
disk line profiles (Smak profiles) to the H line are similar to those
found in several strong black-hole candidates. Measurements of the velocity of
the H line are consistent with an orbital period of 5.1~hours and a
velocity semi-amplitude of the primary of ~\kms. These measurements,
when combined with measurements of the velocity semi-amplitude of the secondary
made by others, indicate that the mass ratio . If the secondary
follows the empirical mass-radius relation found for CVs, the low implies a
primary mass of \mo, and a rather low (face-on) inclination. The
H EW is found to be modulated on the orbital period with a phasing that
implies a partial eclipse of the disk by the secondary, but simultaneous R~band
photometry shows no evidence for such an eclipse.Comment: Accepted for ApJ, plain latex, 5 figures available as self-extracting
uuendoced, compressed, tarfiles (from uufiles
Hawking-like emission in kink-soliton escape from a potential well.
The escape of solitons over a potential barrier is analysed within the framework of a nonlinear Klein–Gordon equation. It is shown that the creation of a kink–antikink pair near the barrier through an internal mode instability can be followed by escape of the kink in a process analogous to Hawking radiation. These results have important implications in a wider context, including stochastic resonance and ratchet systems, which are also discussed
X-ray reflected spectra from accretion disk models. III. A complete grid of ionized reflection calculations
We present a new and complete library of synthetic spectra for modeling the
component of emission that is reflected from an illuminated accretion disk. The
spectra were computed using an updated version of our code XILLVER that
incorporates new routines and a richer atomic data base. We offer in the form
of a table model an extensive grid of reflection models that cover a wide range
of parameters. Each individual model is characterized by the photon index
\Gamma of the illuminating radiation, the ionization parameter \xi at the
surface of the disk (i.e., the ratio of the X-ray flux to the gas density), and
the iron abundance A_{Fe} relative to the solar value. The ranges of the
parameters covered are: 1.2 \leq \Gamma \leq 3.4, 1 \leq \xi \leq 10^4, and 0.5
\leq A_{Fe} \leq 10. These ranges capture the physical conditions typically
inferred from observations of active galactic nuclei, and also stellar-mass
black holes in the hard state. This library is intended for use when the
thermal disk flux is faint compared to the incident power-law flux. The models
are expected to provide an accurate description of the Fe K emission line,
which is the crucial spectral feature used to measure black hole spin. A total
of 720 reflection spectra are provided in a single FITS
file{\url{http://hea-www.cfa.harvard.edu/~javier/xillver/}} suitable for the
analysis of X-ray observations via the atable model in XSPEC. Detailed
comparisons with previous reflection models illustrate the improvements
incorporated in this version of XILLVER.Comment: 70 pages, 21 figures, submitted to Ap
Multi-Temperature Blackbody Spectra of Thin Accretion Disks With and Without a Zero-Torque Inner Boundary Condition
The standard spectral model for analyzing the soft component of thermal
emission from a thin accretion disk around a black hole is the
multi-temperature blackbody (MTB) model. The widely used implementation of this
model, which is known as ``diskbb,'' assumes nonzero torque at the inner edge
of the accretion disk. This assumption is contrary to the classic and current
literature on thin-disk accretion, which advocates the use of a zero-torque
boundary condition. Consequently, we have written code for a zero-torque model,
``ezdiskbb,'' which we compare to the nonzero-torque model diskbb by fitting
RXTE spectra of three well-known black hole binaries: 4U 1543-47, XTE
J1550-564, and GRO J1655-40. The chief difference we find is that the
zero-torque model gives a value for the inner disk radius that is about 2.2
times smaller than the value given by diskbb. This result has important
implications, especially for the determination of black-hole angular momentum
and mass accretion rate.Comment: 27 pages, 9 figures, submitted to Ap
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
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
Simultaneous IUE, EXOSAT and optical observations of the unusual AM Her type variable H058+608
Simultaneous observations of the AM Her type variable H0538+608 made with IUE, EXOSAT, and a 1.3 m ground based telescope, and subsequent optical spectrophotometry at high and low resolution are discussed. The X-ray and optical data show clear evidence of a 3.30 + or - 0.03 hr period. Three SWP spectra were taken outside of eclipse and during overlapping phase intervals. The UV spectra contain strong emission lines characteristic of this class of objects and a flat continuum which appears to be deficient, given the brightness of source at optical and X-ray wavelengths. There is evidence for intensity variations in emission lines, particularly C IV. The X-ray light curves for H0538+608 reveal behavior which may be related to irregularities in its accretion flow
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