HOT PLASMAS AND THE GENERATION OF GAMMA-RAYS

The generation of gamma rays by compact thermal plasmas is reviewed. The recent hard X-ray results from the OSSE on CGRO and SIGMA on Granat have highlighted the need for thermal models for the high-energy radiation from active galactic nuclei in Seyfert galaxies. Pair production in compact sources limits the plasma temperature to approximately 0.1-0.3m(e)c2, which is similar to the range inferred from the data on Seyfert galaxies and Galactic black hole candidates. Thermalization and optical depth problems are raised for compact thermal models and the complications from reflection and variability discussed. New models which incorporate the complications are outlined.