1999A&AS..138..491R

There is now a consensus that gamma-ray bursts involve extraordinary power outputs, and highly relativistic dynamics. The trigger is probably a binary merger or collapse involving compact objects. The most plausible progenitors, ranging from NS-NS mergers to various hypernova-like scenarios, eventually lead to the formation of a black hole with a debris torus around it, the extractable energy being up to 10⁵⁴ergs. The various modes of energy extraction from such systems are discussed. Some key theoretical issues are highlighted, along with the types of observation that would discriminate among the various models.