Title: 

A Mystery and a Tool: 
The Energetics and Host Galaxies of Gamma-Ray Bursts



Edo Berger
Caltech


Abstract:


For the better part of three decades the origin of gamma-ray bursts
was shrouded in mystery.  However, the discovery of afterglows in
1997 revealed that GRBs occur at cosmological distances, are possibly
the most brilliant explosions in the Universe, and are associated
with the death of massive stars and the birth of black holes.
Furthermore, along with this growing knowledge came the realization
that GRBs are a powerful cosmological probe.  In this talk I will
discuss two recent systematic studies, using observations from radio
to X-rays, designed to (i) study GRB energetics as a clue to the
nature of the explosion mechanism, and (ii) study in detail the host
galaxies of GRBs and their relation to other samples of high redshift
galaxies.  In both cases we find surprising results.  First, GRB
explosions appear to be more standard than previously thought when
the total explosive yield is considered, but differ significantly
from supernovae.  Thus, there is a clear dichotomy in stellar
explosions.  Second, GRBs select a wide range of star-forming
galaxies, including some which are very dusty but blue. The latter
are currently missing in radio and submillimeter surveys and their
selection is perhaps related to the association of GRBs with young,
massive stars.