The Edge of a Gamma Ray Burst Afterglow
  We discuss the formation of spectral features in the decelerating ejecta of gamma-ray bursts, including the possible effect of inhomogeneities. These should lead to blueshifted and broadened absorption edges and resonant features, especially from H and He. An external neutral ISM could produce detectable H and He, as well as Fe X-ray absorption edges and lines. Hypernova scenarios may be diagnosed by Fe K-$\alpha$ and H Ly-$\alpha$ emission lines. 
P. Meszaros (1) & M.J. Rees (2) ((1) Pennsylvania State University;   (2) Inst. of Astronomy, Cambridge University)