PHYSICAL PROPERTIES OF RAPIDLY DECAYING AFTERGLOWS

Abstract

We analyze a sample of Swift X-ray and optical GRB afterglows which were chosen so as to reduce selection effects against the weakest events. We tentatively identify important differences in GRBs that show a fast decay with respect to the average GRB, in particular a tendency for the more energetic bursts to have a steeper afterglow decline. An explanation to this finding could be bursts in a wind environment are on average more energetic than bursts occurring in a constant density medium.