Dr. Ehud Nakar (Caltech)

Date: Nov. 19, 2006

Title: Short gamma-ray bursts: cosmic explosions - the last frontier

Abstract:

Gamma-ray bursts (GRBs) are intense flashes of gamma-rays that mark the
explosive death of stellar objects and the birth of black-holes.  Two types
of GRBs are observed: short duration hard spectrum GRBs and long duration
soft spectrum GRBs. While it is known for several years now that long GRBs
are produced by cosmic ultra-relativistic outflows that are launched
following the collapse of massive stars, the origin of short GRBs remained a
complete mystery until recently. The breakthrough came last year with the
first detection of short GRB afterglows, long wavelength emission that
follows the burst of gamma-rays.  These observations established that short
GRBs are cosmological relativistic explosions as well, but unlike their long
relatives they do not originate from massive stars. Instead, the leading
progenitor candidate is double neutron star merger, in which case short GRBs
are electromagnetic counterparts of strong gravitational-wave signal, which
is probably the most accessible to ground-based observatories. The
theoretical progress in the study of short GRBs, following the recent
pivotal discoveries, is reviewed.