Status of models for gamma ray bursts

The nature of gamma-ray bursts, an enigma for more than 25 years, is now co ming into focus. They involve extraordinary power outputs, and highly relat ivistic dynamics. The "trigger" is probably a binary merger or collapse inv olving stellar-mass compact objects. The most plausible progenitors, rangin g from NS-NS mergers to various hypernova-like scenarios, eventually lead t o the formation of a black hole with a debris torus around it, the extracta ble energy being up to 10(54) ergs. Magnetic fields may exceed 10(15) G. De tails of the afterglow may be easier to understand than the initial trigger . Bursts at very high redshift can be astronomically-important as probes of the distant universe.