Nonthermal synchrotron pair cascades in strong magnetic fields: A gamma ray burst emission model

There are several indications that the astrophysical phenomenon of gamma-ray bursts (GRB) may arise in the strong (;This work leads to a study of quantum synchrotron emission, resonant Compton scattering and pair annihilation in strong magnetic fields. The resulting annihilation line is narrow due to the fact that both synchrotron radiation losses and multiple Compton scatterings have cooled particles in the ground state on timescales shorter than annihilation. The pairs come into equilibrium with the photons at an energy which is comparable to the cyclotron energy, and form a peak at that energy which has a width of the same magnitude. When resonant Compton scattering is included, diffusion replaces free streaming as an escape mechanism, efficiently trapping particles by scattering them to low velocities and allowing large numbers to participate in annihilation. These results have significance in constraining the intrinsic luminosities of burst sources when strong fields are present. We have also compiled our results on the observability of the annihilation line as a function of several different physical parameters.