Pair production, Comptonization and dynamics in astrophysical plasmas

Electron-positron pair production is an important cooling mechanism for plasmas at mildly relativistic temperatures. A thorough understanding of the process is necessary to explain the hard X-ray spectra of AGNs and γ-ray bursters. Thermal plasmas with temperatures kT approx.= msub(e)c2 and optical depths 1 <approx. tau <approx. 5, including pair processes, Comptonization and bremsstrahlung are investigated. Results are presented for equilibrium and impulsively heated models. Non-thermal pair production is then discussed in plasmas confined by strong magnetic fields, such as those thought to exist at the surface of neutron stars. Finally simple dynamical systems and the effect of expansion on the spectrum of a gas in which pair production is important are considered. (author)