202 research outputs found
Keck Infrared Observations of GRO J0422+32 in Quiescence
We present Keck K-band photometry and low-resolution H & K-band spectroscopy
of the X-ray nova GRO J0422+32 obtained while the system was in the quiescent
state. No clear ellipsoidal modulation is present in the light curve, which is
instead dominated by a strong flickering component. In the K-band we observe
strong Br_gamma emission, with an equivalent width of 38 +/- 5 Angstroms. From
this we conclude that the accretion disc is the most likely source of the
observed photometric contamination, and that previous infrared-based attempts
to constrain the mass of the putative black hole in this system are prone to
considerable uncertainty. We finally proceed to show how it is possible to
place meaningful constraints on some of the binary parameters of this system,
even in the presence of a relatively high level of contamination from the disc.Comment: 7 pages, 6 figures & 1 table. Accepted for publication in MNRA
Multiwavelength Observations of GX 339-4 in 1996. III. Keck Spectroscopy
As part of our multiwavelength campaign of observations of GX 339-4 in 1996
we present our Keck spectroscopy performed on May 12 UT. At this time, neither
the ASM on the RXTE nor BATSE on the CGRO detected the source. The optical
emission was still dominated by the accretion disk with V approximately 17 mag.
The dominant emission line is H alpha, and for the first time we are able to
resolve a double peaked profile. The peak separation Delta v = 370 +/- 40 km/s.
Double peaked H alpha emission lines have been seen in the quiescent optical
counterparts of many black hole X-ray novae. However, we find that the peak
separation is significantly smaller in GX 339-4, implying that the optical
emission comes from a larger radius than in the novae. The H alpha emission
line may be more akin to the one in Cygnus X-1, where it is very difficult to
determine if the line is intrinsically double peaked because absorption and
emission lines from the companion star dominate.Comment: Submitted to Astrophysical Journal. 10 pages. 2 figure
A Catalog of Transient X-ray Sources in M31
From October 1999 to August 2002, 45 transient X-ray sources were detected in
M31 by Chandra and XMM-Newton. We have performed spectral analysis of all
XMM-Newton and Chandra ACIS detections of these sources, as well as flux
measurements of Chandra HRC detections. The result is absorption-corrected
X-ray lightcurves for these sources covering this 2.8 year period, along with
spectral parameters for several epochs of the outbursts of most of the
transient sources. We supply a catalog of the locations, outburst dates, peak
observed luminosities, decay time estimates, and spectral properties of the
transient sources, and we discuss similarities with Galactic X-ray novae. Duty
cycle estimates are possible for 8 of the transients and range from 40% to 2%;
upper limits to the duty cycles are estimated for an additional 15 transients
and cover a similar range. We find 5 transients which have rapid decay times
and may be ultra-compact X-ray binaries. Spectra of three of the transients
suggest they may be faint Galactic foreground sources. If even one is a
foreground source, this suggests a surface density of faint transient X-ray
sources of >~1 deg.Comment: 63 pages, 22 figures, 3 tables, accepted for publication in Ap
Optical Photometry and Spectroscopy of the Accretion-Powered Millisecond Pulsar HETE J1900.1-2455
We present phase resolved optical photometry and spectroscopy of the
accreting millisecond pulsar HETE J1900.1-2455. Our R-band light curves exhibit
a sinusoidal modulation, at close to the orbital period, which we initially
attributed to X-ray heating of the irradiated face of the secondary star.
However, further analysis reveals that the source of the modulation is more
likely due to superhumps caused by a precessing accretion disc. Doppler
tomography of a broad Halpha emission line reveals an emission ring, consistent
with that expected from an accretion disc. Using the velocity of the emission
ring as an estimate for the projected outer disc velocity, we constrain the
maximum projected velocity of the secondary to be 200 km/s, placing a lower
limit of 0.05 Msun on the secondary mass. For a 1.4 Msun primary, this implies
that the orbital inclination is low, < 20 degrees. Utilizing the observed
relationship between the secondary mass and orbital period in short period
cataclysmic variables, we estimate the secondary mass to be ~0.085 Msun, which
implies an upper limit of ~2.4 Msun for the primary mass.Comment: 8 pages, 6 figures; Accepted for publication in MNRAS. Minor
revisions to match final published versio
RXTE Studies of X-ray Spectral Variations with Accretion Rate in 4U 1915-05
We present the results of detailed spectral studies of the ultra-compact low
mass X-ray binary (LMXB) 4U 1915-05 carried out with the Rossi X-ray Timing
Explorer (RXTE) during 1996. 4U 1915-05 is an X-ray burster (XRB) known to
exhibit a ~199-day modulation in its 2--12 keV flux. Observations were
performed with the PCA and HEXTE instruments on RXTE at roughly one-month
intervals to sample this long-term period and study accretion rate-related
spectral changes. We obtain good fits with a model consisting of a blackbody
and an exponentially cut-off power law. The spectral parameters are strongly
correlated with both the broad-band (2--50 keV) luminosity and the position in
the color-color diagram, with the source moving from a low hard state to a high
soft state as the accretion rate increases. The blackbody component appears to
drive the spectral evolution. Our results are consistent with a geometry in
which the soft component arises from an optically thick boundary layer and the
hard component from an extended Comptonizing corona. Comparing our results with
those of a similar study of the brighter source 4U 1820-30 (Bloser et al.
2000), we find that the two ultra-compact LMXBs occupy similar spectral states
even though the transitions occur at very different total luminosities.Comment: 27 pages LaTeX, 8 figures, accepted to the Astrophysical Journa
Treatment of steroid-induced elevated intraocular pressure with anecortave acetate: a randomized clinical trial.
PURPOSE: The present study is the first randomized clinical trial designed to evaluate the intraocular pressure (IOP)-lowering effect of anecortave acetate (AA) administered at 3 doses (3, 15, or 30 mg) as an anterior juxtascleral depot (AJD) in patients experiencing elevated IOP due to corticosteroid therapy.
METHODS: This was a double-masked, randomized, placebo-controlled, multicenter, parallel group trial. Eligible patients had an IOP of at least 24 mmHg and an IOP increase of at least 10 mmHg relative to their IOP before treatment with steroids. A target IOP was established for each patient at baseline. Patients were randomized to 1 of the 4 treatment groups: vehicle, 3 mg AA, 15 mg AA, or 30 mg AA. All patients then received a 0.5 mL AJD of the assigned treatment. Patients returned for scheduled examination visits at weeks 1, 2, 4, 6, months 3, 4, 5, and 6. IOP was measured at each visit as well as best corrected visual acuity (logMAR), ocular motility, eyelid responsiveness, slit lamp examination, and assessment of any adverse events. In addition, at baseline and at exit, a dilated fundus examination was carried out and the lens was examined using LOCS II criteria.
RESULTS: Seventy patients were randomized to treatment. At week 4, eyes in the vehicle group showed a 3.4 mmHg (9.1%) decrease from baseline. Reductions for the 3 mg AA (3.1 mmHg, 10.7%) and the 30 mg AA groups (5.4 mmHg, 16.6%) were not significantly different than for vehicle control. However, IOP for the 15 mg AA group at week 4 was reduced 11.5 mmHg (31.3%) from baseline, which was statistically significant (P=0.0487). The mean time to treatment failure was 32.2, 38.9, 56.3, and 32.6 days for the vehicle, 3 mg AA, 15 mg AA, and 30 mg AA groups, respectively. Adverse events were assessed at each post-treatment visit. There were no serious adverse events that were determined to be related to the test article or its administration.
CONCLUSIONS: AA can be of benefit to some patients requiring treatment with corticosteroids, but suffering from the side effect of elevated IOP
Multi-wavelength observations of the binary system PSR B1259−63/LS 2883 around the 2014 periastron passage
We report on the results of the extensive multi-wavelength campaign from optical to GeV γ-rays of the 2014 periastron passage of PSR B1259−63, which is a unique high-mass γ-ray emitting binary system with a young pulsar companion. Observations demonstrate the stable nature of the post-periastron GeV flare and prove the coincidence of the flare with the start of rapid decay of the Hα equivalent width, usually interpreted as a disruption of the Be stellar disc. Intensive X-ray observations reveal changes in the X-ray spectral behaviour happening at the moment of the GeV flare. We demonstrate that these changes can be naturally explained as a result of synchrotron cooling of monoenergetic relativistic electrons injected into the system during the GeV flare
Black Holes at Future Colliders and Beyond: a Topical Review
One of the most dramatic consequences of low-scale (~1 TeV) quantum gravity
in models with large or warped extra dimension(s) is copious production of mini
black holes at future colliders and in ultra-high-energy cosmic ray collisions.
Hawking radiation of these black holes is expected to be constrained mainly to
our three-dimensional world and results in rich phenomenology. In this topical
review we discuss the current status of astrophysical observations of black
holes and selected aspects of mini black hole phenomenology, such as production
at colliders and in cosmic rays, black hole decay properties, Hawking radiation
as a sensitive probe of the dimensionality of extra space, as well as an
exciting possibility of finding new physics in the decays of black holes.Comment: 31 pages, 10 figures To appear in the Journal of Physics
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