Title:

Gamma-Ray Bursts from a Safe Distance



Andy Fruchter
StScI



Abstract:

Gamma-Ray Bursts are explosions of unrivalled brilliance.
They can be bright enough to be seen across cosmological
distances with only a pair of binoculars, and can appear to
emit the energy of the rest mass of the sun in high-energy
photons in a matter of seconds.  I will show evidence that
most of these bursts, the so-called long, soft bursts, are
produced by the collapse of extremely massive stars
generally in faint, rapidly star-forming galaxies.  This
choice of host appears to be due to a preference (and
perhaps necessity) of long-duration bursts being formed from
sub-solar metallicity stars.  The astrophysical origin of a
smaller subset of bursts, the short, hard bursts, remains a
mystery.  It has long been suspected that these bursts are
formed by the merger of double neutron star binaries.  There
is as yet no direct evidence for this hypothesis, however,
and a naive interpretation of the data might even argue
against this scenario.  Short bursts do not appear to be too
particular in their choice of hosts.  They are found in both
small star forming galaxies and ellipticals in Abell
Clusters.