Surface and magnetospheric physics of neutron stars and gamma-ray bursts

Various aspects of the surface and magnetospheric physics of neutron stars that may have relevance to gamma-ray bursts if they originate on strongly magnetic neutron stars are reviewed. It is pointed out that since the cohesive energy of matter in a strong magnetic field is uncertain, it is not known whether the stellar surface is likely to be liquid or solid. The confinement of the hot plasma by the magnetic field necessitates that the emission come from near the stellar surface. Whether in a strong magnetic field or not, the burst durations are significantly longer than the cooling time scale of the hot plasma and are deemed to require a separate explanation. Cyclotron cooling is more rapid than pair annihilation and can account for the relatively narrow annihilation lines observed in a number of burst spectra. It is believed that the low-energy absorption features seen in many burst spectra are probably the result of time-averaging spectra in which the low-energy cutoff varies rapidly. If this is the case, the features cannot be used to directly infer the strength of the magnetic field. Either the emission region is extremely optically thick to electron and, especially, cyclotron scattering, or energy and/or matter is continuously replenished during the burst