The central engine of gamma-ray bursters

Cosmic gamma-ray bursts (GRBs) are thought to be created when relativistic blast waves that are powered by "central engines" emit gamma rays between 10 and 10,000 AU from where the explosive energy has been released. To account for the observed duration and variability of GRBs, the central engines must remain active from several to very many seconds and must usually fluctuate strongly in their output on much shorter timescales. We show how neutron stars that are initially rotating differentially at millisecond periods could be such engines, emitting, on the observed timescales, energetic pulses of the right variety and power for as long as the differential motion remains sufficiently vigorous. The energy stored in the differential rotation would be released mainly in sub-bursts, as toroidal magnetic fields are repeatedly wound up to similar to 10(17) G and, only then, pushed to and through the surface by buoyant forces. The same mechanism could also operate in nuclear density tori. The differentially rotating neutron stars or tori could be formed in several ways and at rates sufficiently high to explain the observed frequency of occurrence of GRBs.