The optical afterglow of the short γ-ray burst GRB 050709

Abstract

It has long been known that there are two classes¹ of γ-ray bursts (GRBs), mainly distinguished by their durations. The breakthrough in our understanding of long-duration GRBs (those lasting more than ∼ 2 s), which ultimately linked them with energetic type Ic supernovae^2,3,4, came from the discovery of their long-lived X-ray⁵ and optical^6,7 ‘afterglows’, when precise and rapid localizations of the sources could finally be obtained. X-ray localizations have recently become available^8,9 for short (duration 10 afterglow properties 34 h after the GRB are reminiscent of the afterglows of long GRBs, which are attributable to synchrotron emission from ultrarelativistic ejecta. We did not, however, detect a supernova, as found in most nearby long GRB afterglows, which suggests a different origin for the short GRBs.