  Gamma-Ray Bursts (GRBs) fall into two classes: short-hard and long-soft
bursts. The latter are now known to have X-ray and optical afterglows, to occur
at cosmological distances in star-forming galaxies, and to be associated with
the explosion of massive stars. In contrast, the distance scale, the energy
scale, and the progenitors of short bursts have remained a mystery. Here we
report the discovery of a short-hard burst whose accurate localization has led
to follow-up observations that have identified the X-ray afterglow and (for the
first time) the optical afterglow of a short-hard burst. These, in turn, have
led to identification of the host galaxy of the burst as a late-type galaxy at
z=0.16 showing that at least some short-hard bursts occur at cosmological
distances in the outskirts of galaxies, and are likely to be due to the merging
of compact binaries.
