Changes in the annihilation regime near the surface of a neutron star

Superstrong magnetic fields in the magnetospheres of neutron stars influence the characteristics of the annihilation processes. Besides the change of the cross-section of the process e+e− ← 2γ the process e+e− ← 1γ takes place also. The relative contribution of these two channels depends very strongly on the magnetic field strength, and small fluctuations of the field near the value B ∼ 1013 G may alter the annihilation regime. We discuss possible mechanisms which may lead to changes of magnetic field and their observational consequences. We propose that these processes will be relevant to our understanding of the variability of annihilation lines produced at the surface of pulsars.