0 A Central Engine for Cosmic Gamma - Ray Burst Sources

One of a family previously proposed " central engines " for cosmic gamma-ray burst sources (Klu´zniak & Ruderman 1998) is considered in some detail. A steadily accreting 10 6 Gauss magnetic white dwarf should ultimately collapse to a strongly differentially rotating, millisecond-rotation-period neutron star for a wide range of steady accretion rates and initial masses if the accreting white dwarf has an evolved ONe -Mg composition. A similar neutron star could also result from an initial CO white dwarf but only for more constrained accretion rates. Because the collapsing white dwarf begins as a γ = 4/3 polytrope, the final neutron star's spin-rate increases strongly with cylindrical radius. A stable wind-up of the neutron star's poloidal magnetic field then produces buoyant magnetic toroids which grow, break loose, rise, and partly penetrate the neutron star surface to form a transient, B ≈ 10 17 G millisecond spin-period pulsar with a powerful pulsar wind (Usov 1992). This pulsar wind emission is then rapidly suppressed by the surface shear motion from the strong stellar differential rotation. This wind-up and transient pulsar formation can occur at other times on different cylinders and/or repeat on the same one, with (rewind d up and surface penetration time scales hugely longer than the neutron star's millisecond spin period. In this way, differential rotation 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 sources (total energy, duration, sub-burst fluctuations and time scales, variability among burst events, and baryon loading). Subject headings: gamma rays: bursts — instabilities — magnetic fields — – 3 – stars: neutron — stars: rotation – 4 –