Gamma-Rays from Close Binary Systems

The possibility of producing γ-rays in a close binary system is examined. First the case of systems containing a young pulsar is discussed. It is shown that high energy radiation should be efficiently produced at a shock front, where the pressure of the relativistic wind of the pulsar equals the ram pressure of the primary star wind. The expected number of such systems in the Galaxy is evaluated and the model is applied in some detail to the cases of Cyg X-3 and LSI + 61°.303, two binary systems which are possibly sources of γ-rays. In the second part of the paper, models of accreting black holes are considered with accretion rates as may occur in close binary systems. If electrons and protons are thermally decoupled, the proton temperature, in the vicinity of the hole horizon, is large enough for pion production. However the γ-ray luminosity and spectrum indicate that the process is of little interest for explaining the γ-ray sources discovered by the COS-B satellite. Accretion models where there is a non thermal component in the particle energy distribution may be relevant to γ-ray astronomy.