360 research outputs found
Gamma-Ray Burster Counterparts: HST Blue and Ultraviolet Data
The surest solution of the Gamma Ray Burst (GRB) mystery is to find an
unambiguous low-energy quiescent counterpart. However, to date no reasonable
candidates have been identified in the x-ray, optical, infrared, or radio
ranges. The Hubble Space Telescope (HST) has now allowed for the first deep
ultraviolet searches for quiescent counterparts. This paper reports on
multiepoch ultraviolet searches of five GRB positions with HST. We found no
sources with significant ultraviolet excesses, variability, parallax, or proper
motion in any of the burst error regions. In particular, we see no sources
similar to that proposed as a counterpart to the GRB970228. While this negative
result is disappointing, it still has good utility for its strict limits on the
no-host-galaxy problem in cosmological models of GRBs. For most cosmological
models (with peak luminosity 6X10^50 erg/s), the absolute B magnitude of any
possible host galaxy must be fainter than -15.5 to -17.4. These smallest boxes
for some of the brightest bursts provide the most critical test, and our limits
are a severe problem for all published cosmological burst models.Comment: 15 pages, 2 ps figures, accepted for publication in the Astrophysical
Journa
Complete solution of a constrained tropical optimization problem with application to location analysis
We present a multidimensional optimization problem that is formulated and
solved in the tropical mathematics setting. The problem consists of minimizing
a nonlinear objective function defined on vectors over an idempotent semifield
by means of a conjugate transposition operator, subject to constraints in the
form of linear vector inequalities. A complete direct solution to the problem
under fairly general assumptions is given in a compact vector form suitable for
both further analysis and practical implementation. We apply the result to
solve a multidimensional minimax single facility location problem with
Chebyshev distance and with inequality constraints imposed on the feasible
location area.Comment: 20 pages, 3 figure
Geomechanical analysis of a welding salt layer and its effects on adjacent sediments
AbstractWe simulate welding of the source layer of a salt diapir with a forward finite-element model and study stresses and deformation in the salt layer and the diapir, as well as in their adjacent sediments. Welded salt layers are abundant in mature salt basins, where most or all of the salt has withdrawn into diapirs. However, there is little understanding of the stress field in these layers and their adjacent sediments. We show that salt flow along the source layer leads to significant stress anomalies inside the layer and in adjacent sediments. In the source layer, salt pressure becomes higher than overburden stress in nearly welded areas and becomes lower than overburden stress in adjacent thicker areas. When the source layer welds, stresses increase significantly in sediments near the weld tip, which helps compaction of these sediments and possibly their fracturing and faulting. Our model illustrates that all sediments overlying the weld experience this stress increase and the associated material changes as the weld tip propagates along the weld. We present natural examples fitting our predictions and discuss the importance of our results for the exploration, characterization, and production of reservoirs near welded salt layers
Detection of an optical transient following the 13 March 2000 short/hard gamma-ray burst
We imaged the error box of a gamma-ray burst of the short (0.5 s), hard type
(GRB 000313), with the BOOTES-1 experiment in southern Spain, starting 4 min
after the gamma-ray event, in the I-band. A bright optical transient (OT
000313) with I = 9.4 +/- 0.1 was found in the BOOTES-1 image, close to the
error box (3-sigma) provided by BATSE. Late time VRIK'-band deep observations
failed to reveal an underlying host galaxy. If the OT 000313 is related to the
short, hard GRB 000313, this would be the first optical counterpart ever found
for this kind of events (all counterparts to date have been found for bursts of
the long, soft type). The fact that only prompt optical emission has been
detected (but no afterglow emission at all, as supported by theoretical models)
might explain why no optical counterparts have ever been found for short, hard
GRBs.This fact suggests that most short bursts might occur in a low-density
medium and favours the models that relate them to binary mergers in very
low-density enviroments.Comment: Revised version. Accepted for publication in Astronomy and
Astrophysics Letters, 5 pages, 3 figure
The bright optical flash from GRB 060117
We present a discovery and observation of an extraordinarily bright prompt
optical emission of the GRB 060117 obtained by a wide-field camera atop the
robotic telescope FRAM of the Pierre Auger Observatory from 2 to 10 minutes
after the GRB. We found rapid average temporal flux decay of alpha = -1.7 +-
0.1 and a peak brightness R = 10.1 mag. Later observations by other instruments
set a strong limit on the optical and radio transient fluxes, unveiling an
unexpectedly rapid further decay. We present an interpretation featuring a
relatively steep electron-distribution parameter p ~ 3.0 and providing a
straightforward solution for the overall fast decay of this optical transient
as a transition between reverse and forward shock.Comment: Accepted to A&A, 4 pages, corected few typos pointed out by X.F. W
The Host Galaxy and Optical Light Curve of the Gamma-Ray Burst GRB 980703
We present deep HST/STIS and ground-based photometry of the host galaxy of
the gamma-ray burst GRB 980703 taken 17, 551, 710, and 716 days after the
burst. We find that the host is a blue, slightly over-luminous galaxy with
V_gal = 23.00 +/- 0.10, (V-R)_gal = 0.43 +/- 0.13, and a centre that is
approximately 0.2 mag bluer than the outer regions of the galaxy. The galaxy
has a star-formation rate of 8-13 M_sun/yr, assuming no extinction in the host.
We find that the galaxy is best fit by a Sersic R^(1/n) profile with n ~= 1.0
and a half-light radius of 0.13 arcsec (= 0.72/h_100 proper kpc). This
corresponds to an exponential disk with a scale radius of 0.22 arcsec (=
1.21/h_100 proper kpc). Subtracting a fit with elliptical isophotes leaves
large residuals, which suggests that the host galaxy has a somewhat irregular
morphology, but we are unable to connect the location of GRB 980703 with any
special features in the host. The host galaxy appears to be a typical example
of a compact star forming galaxy similar to those found in the Hubble Deep
Field North. The R-band light curve of the optical afterglow associated with
this gamma-ray burst is consistent with a single power-law decay having a slope
of alpha = -1.37 +/- 0.14. Due to the bright underlying host galaxy the late
time properties of the light-curve are very poorly constrained. The decay of
the optical light curve is consistent with a contribution from an underlying
Type Ic supernova like SN1998bw, or a dust echo, but such contributions cannot
be securely established.Comment: 9 pages, 5 figures, LaTeX using A&A Document Class v4.05, to appear
in A&
Measuring Black Hole Spin in OJ287
We model the binary black hole system OJ287 as a spinning primary and a
non-spinning secondary. It is assumed that the primary has an accretion disk
which is impacted by the secondary at specific times. These times are
identified as major outbursts in the light curve of OJ287. This identification
allows an exact solution of the orbit, with very tight error limits. Nine
outbursts from both the historical photographic records as well as from recent
photometric measurements have been used as fixed points of the solution: 1913,
1947, 1957, 1973, 1983, 1984, 1995, 2005 and 2007 outbursts. This allows the
determination of eight parameters of the orbit. Most interesting of these are
the primary mass of , the secondary mass , major axis precession rate per period, and the
eccentricity of the orbit 0.70. The dimensionless spin parameter is
(1 sigma). The last parameter will be more tightly
constrained in 2015 when the next outburst is due. The outburst should begin on
15 December 2015 if the spin value is in the middle of this range, on 3 January
2016 if the spin is 0.25, and on 26 November 2015 if the spin is 0.31. We have
also tested the possibility that the quadrupole term in the Post Newtonian
equations of motion does not exactly follow Einstein's theory: a parameter
is introduced as one of the 8 parameters. Its value is within 30% (1 sigma) of
the Einstein's value . This supports the of black
holes within the achievable precision. We have also measured the loss of
orbital energy due to gravitational waves. The loss rate is found to agree with
Einstein's value with the accuracy of 2% (1 sigma).Comment: 12 pages, 4 figures, IAU26
Observation of contemporaneous optical radiation from a gamma-ray burst
The origin of gamma-ray bursts (GRBs) has been enigmatic since their
discovery. The situation improved dramatically in 1997, when the rapid
availability of precise coordinates for the bursts allowed the detection of
faint optical and radio afterglows - optical spectra thus obtained have
demonstrated conclusively that the bursts occur at cosmological distances. But,
despite efforts by several groups, optical detection has not hitherto been
achieved during the brief duration of a burst. Here we report the detection of
bright optical emission from GRB990123 while the burst was still in progress.
Our observations begin 22 seconds after the onset of the burst and show an
increase in brightness by a factor of 14 during the first 25 seconds; the
brightness then declines by a factor of 100, at which point (700 seconds after
the burst onset) it falls below our detection threshold. The redshift of this
burst, approximately 1.6, implies a peak optical luminosity of 5 times 10^{49}
erg per second. Optical emission from gamma-ray bursts has been generally
thought to take place at the shock fronts generated by interaction of the
primary energy source with the surrounding medium, where the gamma-rays might
also be produced. The lack of a significant change in the gamma-ray light curve
when the optical emission develops suggests that the gamma-rays are not
produced at the shock front, but closer to the site of the original explosion.Comment: 10 pages, 2 figures. Accepted for publication in Nature. For
additional information see http://www.umich.edu/~rotse
Idling Magnetic White Dwarf in the Synchronizing Polar BY Cam. The Noah-2 Project
Results of a multi-color study of the variability of the magnetic cataclysmic
variable BY Cam are presented. The observations were obtained at the Korean
1.8m and Ukrainian 2.6m, 1.2m and 38-cm telescopes in 2003-2005, 56
observational runs cover 189 hours. The variations of the mean brightness in
different colors are correlated with a slope dR/dV=1.29(4), where the number in
brackets denotes the error estimates in the last digits. For individual runs,
this slope is much smaller ranging from 0.98(3) to 1.24(3), with a mean value
of 1.11(1). Near the maximum, the slope becomes smaller for some nights,
indicating more blue spectral energy distribution, whereas the night-to-night
variability has an infrared character. For the simultaneous UBVRI photometry,
the slopes increase with wavelength from dU/dR=0.23(1) to dI/dR=1.18(1). Such
wavelength dependence is opposite to that observed in non-magnetic cataclysmic
variables, in an agreement to the model of cyclotron emission. The principal
component analysis shows two (with a third at the limit of detection)
components of variablitity with different spectral energy distribution, which
possibly correspond to different regions of emission. The scalegram analysis
shows a highest peak corresponding to the 200-min spin variability, its quarter
and to the 30-min and 8-min QPOs. The amplitudes of all these components are
dependent on wavelength and luminosity state. The light curves were fitted by a
statistically optimal trigonometrical polynomial (up to 4-th order) to take
into account a 4-hump structure. The dependences of these parameters on the
phase of the beat period and on mean brightness are discussed. The amplitude of
spin variations increases with an increasing wavelength and with decreasing
brightnessComment: 30pages, 11figures, accepted in Cent.Eur.J.Phy
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