The first localization of a short gamma-ray burst by Swift

Gamma Ray Bursts (GRBs) are bright, brief flashes of high energy photons that have fascinated scientists since their discovery in 1973. They come in two distinct classes: long (>2 s), soft-spectrum bursts and short, hard-spectrum events. The long bursts tend to be at high redshifts (z ~ 1) in sub-luminous star-forming host galaxies and are likely produced in the core-collapse explosion of massive stars. We have now detected X-ray afterglow from and accurately localized a short burst (GRB050509b) for the first time. Its position on the sky is near to a luminous, non-star-forming elliptical galaxy at z = 0.225 located in a cluster. The a posteriori probability of the position being close to such a nearby, luminous galaxy by coincidence is ~0.0001 This supports the model where short bursts are the signature of the fiery merger of neutron star or black hole binaries, as such systems would be preferentially found in or near large ellipticals