Radiative processes underlying the x-ray and gamma-ray continua of active galactic nuclei and gamma-ray bursts

Steady relativistic plasmas are studied. Compton scattering, electron position pair production and annihilation, and bremsstrahlung and synchrotron emission are considered. In the steady state, the pair production rate equals the pair annihilation rate, and the energy production rate equals the electron cooling rate. Two kinds of plasmas are studied: purely thermal plasmas, and two component ones containing nonthermal as well as thermal electrons. The temperatures, electron distributions, and spectra are obtained self-consistently as functions of plasma parameters. The results are applied to two classes of cosmic sources of x-ray and gamma-ray radiation: active galactic nuclei and gamma-ray bursts. The thermal model is found compatible, though unlikely, with the x-ray spectra of active galactic nuclei, and incompatible with the x-ray bursts spectra. The nonthermal models are found preferable for the considered classes of cosmic objects. The spectra of gamma-ray bursts with x-ray spectral index ≅0 and gamma-ray index ≅1-2 are reproduced in the models with low energy density of the primary soft photons. The unique form of the x-ray spectrum results from repeated Compton scatterings by both nonthermal and thermal electrons. The gamma-ray spectra reflect the energy distribution of the input electrons