Possible detection of hard x-ray afterglows of short γ-ray bursts

Abstract

We report the discovery of a transient and fading hard X-ray emission in the BATSE lightcurves of a sample of short γ-ray bursts. We have summed each of the four channel BATSE light curves of 76 short bursts to uncover the average temporal and spectral evolution of a possible transient signal following the prompt flux. We found an excess emission peaking ∼30 s after the prompt one, detectable for ≈100 s. The soft power-law spectrum and the time-evolution of this transient signal suggest that it is produced by the deceleration of a relativistic expanding source, as predicted by the afterglow model.