Delayed hard photons from gamma-ray bursts

Abstract

The delayed hard (up to 25 GeV) photons observed more than an hour following a gamma-ray burst on 1994 February 17 may result from the collisions of relativistic nucleons with a dense cloud, producing π^0^. The required cloud density is ~2 x 10^11^ cm^-3^. This cloud may be the remains of the disrupted envelope of a neutron star, and may survive as an excretion disk of ~10^14^-10^15^ cm radius around the coalescing binary.