PAIR ABSORPTION OF TEV GAMMA-RAYS IN ACCRETING BINARIES

A model to study the absorption and propagation of high energy photons through the radiation field of accretion discs is presented. The model indicates that this absorption process is important for 7-rays with energies between 100 GeV and a few TeV produced near the co-rotation radius of X-ray binary systems with pulse periods of approximately 1 s (4U 0 1 15 + 63, Centaurus X-3 and Hercules X-1) or shorter(Scorpius X-1 and Cygnus X-3). The re-distribution of the primary energy into other photons through electromagnetic cascades is shown to diminish this absorption. The overall process implies a particle luminosity in excess of the Eddington limit for spherical accretion but not unlikely to be produced under other geometries, like accretion columns. A plausible qualitative explanation of conflicting observations of TeV gamma-rays from X-ray binaries is provided by the model; however, a quantitative analysis does not fully explain the discrepancies between imaging and non-imaging observations of 4U 0115 + 63 and Hercules X-1.