Gamma-ray burst sources in strong magnetic fields

Abstract

The synchrotron model of gamma-ray burst sources in magnetic fields approaching the quantum critical value of |$B_c=m^2_ec^3/e\hslash=4.413\times10^{12}\enspace\text G$| is studied, with particular emphasis on the quantum effects that arise and their effect on the spectral emission. These include the reduction of the spectral emissivity below the classical value, and pair production by a single photon in the strong field. The quantum synchrotron continuum is modified by self-absorption at low energies and the pair production at high energies. The increase in spectral index at the pair production absorption turnover is found to be so large that the absorption is effectively a truncation. Equilibrium pair concentrations are accurately calculated by balancing single photon pair production with two photon annihilation, yielding densities corresponding to moderate optical depths. Compton scattering may therefore be quite important. New quantum results for synchrotron radiation and the pair processes improve and extend previous equilibrium calculations. The compactness of burst sources ensures a high pair yield. The cold pairs that annihilate give a 511 keV line spectral line that is marginally observable above the continuum at these densities. The influence of some more exotic processes in strong fields such as photon splitting is also examined. Comparison of observations and theory lend weight to arguments in favour of anisotropic plasmas in burst sources.