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5.2 Gamma Ray Bursts: The Most Luminous Known Cosmic Objects

Some subset of massive stars may give rise to gamma-ray bursts. It may indeed turn out that all the long-duration bursts detected by Beppo-SAX involve some supernova-type event, and that the shorter bursts (maybe less highly beamed) are caused by compact binary coalescence at more modest redshifts. Bursts have already been detected out to z = 3.4; their optical afterglows are 100 times brighter than supernovae. Prompt optical emission concurrent with the 10-100 seconds of the burst itself (observed in one case so far, but expected in others) is more luminous by a further factor 100. Gamma-ray bursts are, however, far rarer than supernovae - even though the afterglow rate could exceed that of the bursts themselves if the gamma rays were more narrowly beamed than the slower-moving ejecta that cause the afterglow. Detection of ultra-luminous optical emission from bursts beyond z = 5 would offer a marvellous opportunity to obtain a high-resolution spectrum of intervening absorption features. (Lamb and Reichart 1999)