6 research outputs found
GRB Spikes Could Resolve Stars
GRBs vary more rapidly than any other known cosmological phenomena. The lower
limits of this variability have not yet been explored. Improvements in
detectors would reveal or limit the actual rate of short GRBs. Were microsecond
"spike" GRBs to exist and be detectable, they would time-resolve stellar mass
objects throughout the universe by their gravitational microlensing effect.
Analyzing the time structure of sufficient numbers of GRB spikes would reveal
or limit , , and/or .Comment: 18 pages, 2 figures, in press: ApJ (Letters
Limits on the cosmological abundance of supermassive compact objects from a millilensing search in gamma-ray burst data
A new search for the gravitational lens effects of a significant cosmological
density of supermassive compact objects (SCOs) on gamma-ray bursts has yielded
a null result. We inspected the timing data of 774 BATSE-triggered GRBs for
evidence of millilensing: repeated peaks similar in light-curve shape and
spectra. Our null detection leads us to conclude that, in all candidate
universes simulated, is favored for , while in some universes and mass ranges the density
limits are as much as 10 times lower. Therefore, a cosmologically significant
population of SCOs near globular cluster mass neither came out of the
primordial universe, nor condensed at recombination.Comment: 14 pages including 3 figures, appeared 2001 January 2
On Suggestive Correlations Between GRBs and Clusters of Galaxies
Recent claims of angular correlations between gamma-ray bursts (GRBs) and
clusters of galaxies are evaluated in light of existing but previously
uncorrelated GRB positional data. Additional GRB data sets we use include
sub-samples of soft BATSE 3B bursts, bursts located by the Interplanetary
Network (IPN), and GRBs localized by COMPTEL. We confirm a previously reported
excess by Rood and Struble (1996) of the 185 rich, nearby clusters of galaxies
(Abell, Corwin, and Olowin 1989, ACO) in the 1- error circles of 74
BATSE 3B positions, but find a typical correlation strength of only
2.5- for typical sub-samples. However, none of the 185 ACO clusters
occur in the 1- error boxes of 40 IPN GRBs or 18 COMPTEL GRBs. When all
ACO clusters are correlated with BATSE 3B GRBs however, we find an increasingly
strong correlation for GRBs with decreasingly small error boxes, reaching above
the 3.5- level. We also find a slight excess of {\it soft} BATSE GRBs
near the positions of 185 rich, nearby ACO clusters, but the significance of
the correlation averages only 2.5- for sub-samples delineated by
softness. We caution that the statistical significance of all these
correlations is marginal, and so conclude that the excess is at best only
suggestive of a physical association. Statistical fluke is still a strong
possibility. BATSE could confirm or refute such correlations in a 10-year
lifetime.Comment: 17 pages in LateX including 2 postcript figures. To be published in
ApJ. One affiliation has been change