2 s, and 'short', with durations of T_90 < 2 s (where T_90 is the time to detect 90% of '/>
An origin in the local Universe for some short γ-ray bursts
Gamma-ray bursts (GRBs) divide into two classes: 'long', which typically have initial durations of T_90 > 2 s, and 'short', with durations of T_90 < 2 s (where T_90 is the time to detect 90% of the observed fluence). Long bursts, which on average have softer γ-ray spectra, are known to be associated with stellar corecollapse events—in some cases simultaneously producing wi powerful type Ic supernovae. In contrast, the origin of short bursts has remained mysterious until recently. A subsecond intense 'spike' of γ-rays during a giant flare from the Galactic soft γ-ray repeater, SGR1806-20, reopened an old debate over whether some short GRBs could be similar events seen in galaxies out to ～70 Mpc (refs 6-10; redshift z≈0.016). Shortly after that, localizations of a few short GRBs (with optical afterglows detected in two cases11'12) have shown an apparent association with a variety of host galaxies at moderate redshifts. Here we report a correlation between the locations of previously observed short bursts and the positions of galaxies in the local Universe, indicating that between 10 and 25 per cent of short GRBs originate at low redshifts (z < 0.025).
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