Pair production and annihilation in strong magnetic fields

Abstract

Electromagnetic phenomena occurring in the presence of strong magnetic fields are currently of great interest in high‐energy astrophysics. In particular, the process of pair production by single photons in the presence of field of order 1012 Gauss is of importance in cascade models of pulsar gamma ray emission, and may also become significant in theories of other radiation phenomena whose sources may be neutron stars (e.g., gamma ray bursts). In addition to pair production, the inverse process of pair annihilation is greatly affected by the presence of superstrong magnetic fields. The most significant departures from annihilation processes in free space are a reduction in the total rate for annihilation into two photons, a broadening of the familiar 511‐keV line for annihilation at rest, and the possibility for annihilation into a single photon (which dominates the two‐photon annihilation for B≳1013 Gauss). The physics of these pair conversion processes, which is reviewed briefly, can become quite complex in the teragauss regime, and can involve calculations which are technically difficult to incorporate into models of emission mechanisms in neutron star magnetospheres. However, recent theoretical work, especially in the case of pair annihilation, also suggests potential techniques for more direct measurements of field strengths near the stellar surface.