  Gamma Ray Bursts (GRBs) are bright, brief flashes of high energy photons that
have fascinated scientists for 30 years. They come in two classes: long (>2 s),
softspectrum bursts and short, hard events. The major progress to date on
understanding GRBs has been for long bursts which are typically at high
redshift (z ~ 1) and are in sub-luminous star-forming host galaxies. They are
likely produced in core-collapse explosions of massive stars. Until the present
observation, no short GRB had been accurately (<10") and rapidly (minutes)
located. Here we report the detection of X-ray afterglow from and the
localization of short burst GRB050509b. Its position on the sky is near a
luminous, non-starforming elliptical galaxy at a redshift of 0.225, exactly the
type of location one would expect if the origin of this GRB is the
long-proposed fiery merger of neutron star (NS) or black hole (BH) binaries.
The X-ray afterglow is found to be weak and fading below detection within a few
hours and no optical afterglow is detected to stringent limits, explaining the
past difficulty in localizing short GRBs.
