Discovery of the short gamma-ray burst GRB 050709

TL;DR

This paper reports the discovery and localization of the first optical and X-ray afterglows of a short gamma-ray burst, revealing its cosmological origin and likely progenitors as merging compact binaries.

Contribution

It provides the first precise localization and afterglow detection of a short gamma-ray burst, confirming its cosmological distance and association with galaxy outskirts.

Findings

Short gamma-ray bursts occur at cosmological distances.

They are associated with late-type galaxies.

Likely progenitors are merging compact binaries.

Abstract

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.