Particle acceleration mechanisms in compact sources

Abstract

Various mechanisms capable of accelerating particles to the energies of 10 16 eV or higher that are required to produce ultra-high-energy γ-rays are discussed. The models for sources of VHE and UHE γ-rays which incorporate these mechanisms assume that the acceleration power source is either accretion or neutron star rotation. The current status of the theory will be reviewed in light of the observational requirements on both power and maximum energy of the accelerated particles. Acceleration of protons in a pulsar wind shock seems to be the only model capable of generating both the power and particle energy required to explain UHE emission from Cyg X-3. This mechanism, capable of operating both in supernova remnants and in binary systems containing pulsars, will be discussed in some detail. γ-rays from interactions of protons accelerated by pulsar wind shocks may be detectable from SN1987A as well as several known binary pulsars.