Gamma-ray Burst -supernova Relation

There is growing evidence that long and hard gamma-ray bursts (GRBs), discovered at redshifts between 0.4 and 3.4, are related to some type of supernova (SN) explosions. The GRB ejecta are ultra-relativistic, and possibly beamed. There is a possibility that some SN ejecta are also beamed and/or relativistic. Prospects for farther advances guided by expected and unexpected observational developments are very good. The prospects for developing a sound and quantitative GRB theory any time soon are rather modest, if histories of quasars, radio pulsars and supernovae are used for reference. However, the current progress in the understanding of GRB afterglows (which are relativistic) and remnants (which are non-relativistic) is likely to continue, as these appear to be simpler than the GRBs. According to the current analysis of GRB 970508 the energy of gamma rays released by this event was about the same as the total energy of explosion. If correct, this result is difficult to reconcile with the internal shock models. It also implies that the global energy generation rate by GRBs is four orders of magnitude lower than the rate due to ordinary supernovae, which makes it very unlikely that the highly energetic supernova remnants were created by GRBs.