6,411 research outputs found
HST Observations of GRO J1655-40 in Outburst
We examine the results of a coordinated HST-RXTE-CGRO campaign to study the
microquasar GRO J1655-40 during its 1996-7 outburst, focusing on interpretation
of the overall anti-correlation seen between optical and X-ray fluxes during
the early months of the outburst. Our tools include echo-mapping, optical/UV
continuum spectral modelling and analysis of spectral variability. We conclude
by suggesting one possible interpretation for the anti-correlation.Comment: 4 pages with 11 postscript figures included. To appear in New
Astronomy Reviews, as part of proceedings of 2nd Workshop on Galactic Sources
with Relativistic Jets. Uses newarcrc.sty (included
Echo-Mapping of Swift J1753.5-0127
We present two epochs of coordinated X-ray-optical timing observations of the
black hole candidate Swift J1753.5-0127 during its 2005 outburst. The first
epoch in July occurred at outburst peak. Two consecutive nights of observations
using the McDonald Observatory Argos camera with the Rossi X-ray Timing
Explorer show a consistent correlation with an immediate response and an
extended tail lasting ~5s. The properties of the variability and the
correlation are consistent with thermal reprocessing in an accretion disk. The
shortness of the lag suggests a short orbital period consistent with that
recently claimed. The second epoch in August used the VLT FORS2 HIT mode again
in conjunction with RXTE. Again a repeatable correlation is seen between two
independent subsets of the data. In this case, though, the cross-correlation
function has an unusual structure comprising a dip followed by a double-peak.
We suggest that this may be equivalent to the dip plus single peak structure
seen by Kanbach et al. (2001) in XTE J1118+480 and attributed there to
synchrotron emission; a similar structure was seen during later activity of
Swift J1753.5-0127 by Durant et al. (2008).Comment: 7 pages, accepted for publication in Monthly Notices of the Royal
Astronomical Societ
Hubble Space Telescope Observations of the Black Hole X-ray Transient GRO J0422+32 Near Quiescence
We present HST/FOS ultraviolet and optical spectroscopy of the black hole
X-ray transient GRO J0422+32 shortly before the system reached quiescence. We
find that the accretion spectrum from 2500-9000A can be very well fit by a
self-absorbed synchrotron model, with superposed HI and MgII emission lines.
The explanations we suggest for this spectrum are that it is either due to
active coronal regions above a geometrically thin accretion disc, or that the
disc is evaporated into an advective flow.Comment: 7 pages with 7 postscript figures included, uses mn.sty. Accepted for
publication in MNRA
Factors affecting handling qualities of a lift-fan aircraft during steep terminal area approaches
The XV-5B lift-fan aircraft was used to explore the factors affecting handling qualities in the terminal area. A 10 deg ILS approach task was selected to explore these problems. Interception of the glide slope at 457.2 m, glide slope tracking, deceleration along the glide slope to a spot hover were considered. Variations in airplane deck angle, deceleration schedule, and powered-lift management were studied. The overall descent performance envelope was identified on the basis of fan stall, maximum comfortable descent rate, and controllability restrictions. The collective-lift stick provided precise glide slope tracking capability. The pilot preferred a deck-parallel attitude for which he used powered lift to control glide slope and pitch attitude to keep the angle of attack near zero. Workload was reduced when the deceleration schedule was delayed until the aircraft was well established on the glide slope, since thrust vector changes induced flight path disturbances
The 1996 outburst of GRO J1655-40: disc irradiation and enhanced mass transfer
We show that the 1996 outburst of the X-ray binary transient system GRO
J1655-40 can be explained by the standard dwarf-nova type disc instability,
followed by an episode of enhanced mass transfer from the secondary if the mass
transfer rate in GRO J1655-40 is within a factor < 10 of the stability limit.
We argue that irradiation of the secondary during the onset of the outburst
driven by the thermal instability in the outer disc can increase the mass
transfer rate above the minimum value required for stable accretion. This will
then produce the period of near-constant X-ray emission seen in this system.
This scenario can also explain the observed anti-correlation between the
optical and X-ray fluxes. It is generally accepted that optical emission in
low-mass X-ray binaries is produced by irradiation of the outer disc by X-rays.
There is also strong circumstantial evidence that in order for the outer disc
to see the irradiating flux, it must be warped. Depending on the warp
propagation mechanism, either a burst of mass from the secondary or viscous
decay are likely to decrease the degree of warping, thereby causing the
decrease in the observed optical flux while the X-ray flux remains constant or
even increases, exactly as observed in GRO J1655-40. Finally, the decrease of
the disc warping and, therefore, irradiation will cause the disc to become
unstable once again, terminating the outburst.Comment: Astronomy and Astrophysics - in pres
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