There have been a number of more and less direct indications in recent times that gamma-ray bursts (GRBs) are associated with massive stars. These include their association with blue galaxies, their number counts, their energetics, and more recently the discovery of supernova or supernova-like signatures in their afterglow light curves. I shall discuss some of this evidence, and a specific model for powering GRBs from stellar collapses.
A paradox in all this is that most massive stars are associated with giant molecular clouds, and thus one would expect large extinction towards the majority of GRBs. Recent work by Galama and myself resolves this paradox, by noting that in X rays one infers very large column densities towards almost all GRBs for which the measurement could be done. The inferred properties of the absorbing clouds are exactly like giant molecular clouds in our own Galaxy. The low optical extinction at these large column densities can be explained by dust destruction by the hard radiation from the GRB.
Finally, I shall discuss some of the implications for models and future observational work: the need to examine afterglow evolution in dense environments, and the need for senstive soft X-ray observations of early afterglows.
Received November 17, 2000