4,377 research outputs found
Gamma Ray Burst Host Galaxies Have `Normal' Luminosities
The galactic environment of Gamma Ray Bursts can provide good evidence about
the nature of the progenitor system, with two old arguments implying that the
burst host galaxies are significantly subluminous. New data and new analysis
have now reversed this picture: (A) Even though the first two known host
galaxies are indeed greatly subluminous, the next eight hosts have absolute
magnitudes typical for a population of field galaxies. A detailed analysis of
the 16 known hosts (ten with red shifts) shows them to be consistent with a
Schechter luminosity function with as expected for
normal galaxies. (B) Bright bursts from the Interplanetary Network are
typically 18 times brighter than the faint bursts with red shifts, however the
bright bursts do not have galaxies inside their error boxes to limits deeper
than expected based on the luminosities for the two samples being identical. A
new solution to this dilemma is that a broad burst luminosity function along
with a burst number density varying as the star formation rate will require the
average luminosity of the bright sample (
or ) to be much greater than the
average luminosity of the faint sample ( or ). This places the bright bursts at distances
for which host galaxies with a normal luminosity will not violate the observed
limits. In conclusion, all current evidence points to GRB host galaxies being
normal in luminosity.Comment: 18 pages, 3 figures, Submitted to ApJLet
The Interplanetary Network Supplement to the BeppoSAX Gamma-Ray Burst Catalogs
Between 1996 July and 2002 April, one or more spacecraft of the
interplanetary network detected 787 cosmic gamma-ray bursts that were also
detected by the Gamma-Ray Burst Monitor and/or Wide-Field X-Ray Camera
experiments aboard the BeppoSAX spacecraft. During this period, the network
consisted of up to six spacecraft, and using triangulation, the localizations
of 475 bursts were obtained. We present the localization data for these events.Comment: 89 pages, 3 figures. Submitted to the Astrophysical Journal
Supplement Serie
The distances of short-hard GRBs and the SGR connection
We present a search for nearby (D<100 Mpc) galaxies in the error boxes of six
well-localized short-hard gamma-ray bursts (GRBs). None of the six error boxes
reveals the presence of a plausible nearby host galaxy. This allows us to set
lower limits on the distances and, hence, the isotropic-equivalent energy of
these GRBs. Our lower limits are around erg (at
confidence level); as a consequence, some of the short-hard GRBs we examine
would have been detected by BATSE out to distances greater than 1 Gpc and
therefore constitute a bona fide cosmological population. Our search is
partially motivated by the December 27, 2004 hypergiant flare from SGR 1806-20,
and the intriguing possibility that short-hard GRBs are extragalactic events of
a similar nature. Such events would be detectable with BATSE to a distance of
\~50 Mpc, and their detection rate should be comparable to the actual BATSE
detection rate of short-hard GRBs. The failure of our search, by contrast,
suggests that such flares constitute less than 15% of the short-hard GRBs (<40%
at 95% confidence). We discuss possible resolutions of this discrepancy.Comment: Enlarged sample of bursts; ApJ in pres
Evidence for a Fast Decline in the Progenitor Population of Gamma Ray Bursts and the Nature of their Origin
We show that the source population of long gamma-ray bursts (GRBs) has
declined by at least a factor of 12 (at the 90% confidence level) since the
early stages of the Universe (). This result has been obtained
using the combined BATSE and \it Ulysses \rm GRB brightness distribution and
the detection of four GRBs with known redshifts brighter than 10 erg
s in the 50 - 300 keV range at their peak. The data indicate that the
decline of the GRB source population is as fast as, or even faster than, the
measured decline of the star formation rate. Models for the evolution of
neutron star binaries predict a significantly larger number of apparently
bright GRBs than observed. Thus our results give independent support to the
hypernova model, which naturally explains the fast decline in the progenitor
population.Comment: 7 pages, 6 figures, submitted to ApJ, added reference
Lognormal Properties of SGR 1806-20 and Implications for Other SGR Sources
The time interval between successive bursts from SGR 1806-20 and the
intensity of these bursts are both consistent with lognormal distributions.
Monte Carlo simulations of lognormal burst models with a range of distribution
parameters have been investigated. The main conclusions are that while most
sources like SGR 1806-20 should be detected in a time interval of 25 years,
sources with means about 100 times longer have a probability of about 5\% of
being detected in the same interval. A new breed of experiments that operate
for long periods are required to search for sources with mean recurrence
intervals much longer than SGR 1806-20.Comment: 4 pages, latex with seperate file containing 2 uuencoded, gzip'ed,
tarred, .eps figures. Replaced with file that does not use kluwer.sty to
allow automatic postscript generation. To appear in proceedings of ESLAB 2
The random case of Conley's theorem
The well-known Conley's theorem states that the complement of chain recurrent
set equals the union of all connecting orbits of the flow on the compact
metric space , i.e. , where
denotes the chain recurrent set of , stands for
an attractor and is the basin determined by . In this paper we show
that by appropriately selecting the definition of random attractor, in fact we
define a random local attractor to be the -limit set of some random
pre-attractor surrounding it, and by considering appropriate measurability, in
fact we also consider the universal -algebra -measurability besides -measurability, we are able to obtain
the random case of Conley's theorem.Comment: 15 page
VLT identification of the optical afterglow of the gamma-ray burst GRB 000131 at z=4.50
We report the discovery of the gamma-ray burst GRB 000131 and its optical
afterglow. The optical identification was made with the VLT 84 hours after the
burst following a BATSE detection and an Inter Planetary Network localization.
GRB 000131 was a bright, long-duration GRB, with an apparent precursor signal
62 s prior to trigger. The afterglow was detected in ESO VLT, NTT, and DK1.54m
follow-up observations. Broad-band and spectroscopic observations of the
spectral energy distribution reveals a sharp break at optical wavelengths which
is interpreted as a Ly-alpha absorption edge at 6700 A. This places GRB 000131
at a redshift of 4.500 +/- 0.015. The inferred isotropic energy release in
gamma rays alone was approximately 10^54 erg (depending on the assumed
cosmology). The rapid power-law decay of the afterglow (index alpha=2.25,
similar to bursts with a prior break in the lightcurve), however, indicates
collimated outflow, which relaxes the energy requirements by a factor of < 200.
The afterglow of GRB 000131 is the first to be identified with an 8-m class
telescope.Comment: 8 pages, 7 figures, accepted to A&A Letter
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
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