A central engine for cosmic gamma-ray burst sources

One of a family previously proposed "central engines" for cosmic gamma-ray burst sources is considered in some detail. A steadily accreting 10(6) G ma gnetic white dwarf should ultimately collapse to a strongly differentially rotating, millisecond-rotation-period neutron star for a wide range of stea dy accretion rates and initial masses if the accreting white dwarf has an e volved O-Ne-Mg composition. A similar neutron star could also result from a n initial C-O white dwarf but only for more constrained accretion rates. Be cause the collapsing white dwarf begins as a gamma = 4/3 polytrope, the fin al neutron star's spin rate increases strongly with cylindrical radius. A s table windup of the neutron star's poloidal magnetic field then produces bu oyant magnetic toroids which grow, break loose, rise, and partly penetrate the neutron star surface to form a transient, B approximate to 10(17) G mil lisecond-spin-period pulsar with a powerful pulsar wind. This pulsar wind e mission is then rapidly suppressed by the surface shear motion from the str ong stellar differential rotation. This windup and transient pulsar formati on can occur at other times on different cylinders and/or repeat on the sam e one, with (re-)windup and surface penetration timescales hugely longer th an the neutron star's millisecond spin period. In this way, differential ro tation both opens and closes the doors which allow neutron star spin energy to be emitted in powerful bursts of pulsar wind. Predictions of this model compare favorably to needed central engine properties of gamma-ray burst s ources (total energy, birth rate, duration, subburst fluctuations and times cales, variability among burst events, and baryon loading).