ar X iv : a st ro - p h / 96 12 07 8 v 1 9 D ec 1 99 6 Physical processes in pulsar magnetospheres and non - thermal high - frequency emission

The energy source of a pulsar's non-thermal emission is the rotational energy loss of the neutron star. The rotational energy of the neutron star is transformed into the pulsar radiation by a long sequence of processes. The processes of this sequence are discussed. 1. Introduction The current sample of radio pulsars contains about six hundred pulsars (e.g., Taylor et al. 1993). The radio luminosities of the pulsars are small compared with the energy loss rate due to the pulsar spin down (∼ 10 −6 − 10 −5). Strong high-frequency radiation in the optical, X-ray and γ-ray ranges is observed from a few radio pulsars (for a review, see Thompson 1994; Hartmann 1995). The observed radiated power for these pulsars is concentrated mainly in the γ-ray range. The γ-ray pulsar Geminga is probably also a radio pulsar (Halpern & Holt 1992) which is " radio quiet " because its radio beam does not intersect the Earth (Ozernoy & Usov 1977). The pulsar luminosities in γ-rays are a substantial fraction (∼ 10 −3 − 10 −1) of the spin-down power, ˙ E rot. This makes studies of high-energy radiation of pulsars a promising avenue to a better understanding of physical processes which result in non-thermal radiation of pulsars. A common point of all available models of pulsars is that a strong electric field is generated in the magnetosphere of a rotating magnetized neutron star (e.g., Michel 1991). The component of the electric field E = (E · B)/|B| along the magnetic field B is non-zero, and this E can accelerate particles to ultrarela-tivistic energies. The accelerated particles emit γ-rays due to curvature emission and other processes. Some of these γ-rays are absorbed by creating secondary electron-positron pairs. The created electron-positron pairs screen the electric field E in the pulsar magnetosphere everywhere except for the compact regions. The regions where E is unscreened are called gaps. These gaps are, in fact, an " engine " which is responsible for the pulsar radiation. Two kinds of gap models have been popular in trying to explain the non-thermal radiation of pulsars. The main difference between these two is the site of gaps. A gap that forms near the magnetic poles of the pulsar is called a polar gap. Besides polar-gap models there are also outer-gap models (e. This review mainly concentrates on the polar gap models (about outer gaps, see Romani, these proceedings).