RELATIVISTIC ELECTRON-POSITRON BEAMS IN GAMMA-RAY BURSTERS

Beams of relativistic electrons and/or positrons leaving the surface of a strongly magnetized neutron star may give rise to gamma-ray bursts. The beams could be accelerated by strong, magnetically aligned electric fields that are produced by oscillations of the stellar surface. Here we investigate the particle acceleration in these electric fields, the resulting electron-positron pair cascade, and the gamma-ray emission. We find that beams of electrons and positrons moving parallel to the magnetic field are generated, with a differential energy distribution of approximately dN/depsilon(parallel-to) is-proportional-to epsilon(parallel-to)-2.1 for parallel energies epsilon(parallel-to) above a few tens of MeV. These beams produce the bulk of the gamma-ray burst radiation below approximately 1 MeV by the resonant Compton scattering of thermal photons emitted from the stellar surface. The escaping synchrotron radiation from the cascade dominates the radiation spectrum above approximately 1 MeV.