  The final chapter in the long-standing mystery of the gamma-ray bursts (GRBs)
centres on the origin of the short-hard class, suspected on theoretical grounds
to result from the coalescence of neutron star or black hole binary systems.
Numerous searches for the afterglows of short-hard bursts have been made,
galvanized by the revolution in our understanding of long-duration GRBs that
followed the discovery in 1997 of their broadband (X-ray, optical, and radio)
afterglow emission. Here we present the discovery of the X-ray afterglow of a
short-hard burst whose accurate position allows us to unambiguously associate
it with a star-forming galaxy at redshift z=0.160, and whose optical lightcurve
definitively excludes a supernova association. Together with results from three
other recent short-hard bursts, this suggests that short-hard bursts release
much less energy than the long-duration GRBs. Models requiring young stellar
populations, such as magnetars and collapsars, are ruled out, while coalescing
degenerate binaries remain the most promising progenitor candidates.
