GAMMA-RAY BURSTS FROM MAGNETOSPHERIC PLASMA-OSCILLATIONS

We show that relativistic, (neutron star) magnetospheric plasma oscillations, damped by inverse Compton scatterings with the ambient radiation field, can account for the energetics, decay time scale, and spectra of typical gamma-ray bursts (GRBs). We find that the dissipation time scale τ depends on the energy of the perturbation (the "burst" energy Wburst), and that τ ~∼ 1 s for Wburst ≈ 1036 ergs. We discuss several plausible mechanisms for ""loading" the magnetosphere, all of which might be contributing to the GRB phenomenon. The soft photon source is likely due to backwarming of the reprocessing boundary (i.e., the stellar surface and possibly an accretion disk) by the incipient γ-rays, which is constistent with the Ginga observation of a slowly decaying, low-energy X-ray component in some bursts. The fractional power emitted in γ-rays depends on the maximum Lorentz factor γmax of the oscillating particles. Moderately relativistic oscillations with γmax ≲ 103 can account for some burst spectra with a single upscattered component, but possibly not those that exhibit cyclotron features. Oscillations with γmax ≫ 103 produce very hard γ-ray spectra that are deficient below several hundred keV, as required by the two component (i.e., incipient plus reflected) model for GRBs with absorption lines.