[en] 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

[en] The kinetic equation describing Compton losses of relativistic electrons in an isotropic field of soft background photons is solved exactly including both continuous energy losses in the classical Thomson regime and catastrophic losses in the quantum Klein-Nishina regime. This extends the previous treatments of this problem, which assumed the validity of either one of these regimes alone. The problem is relevant to astrophysical sources containing relativistic electrons. Analytical solutions for the steady state electron and gamma-ray spectra in the case of power-law soft photons and monoenergetic and power-law electron injections are obtained. Numerical solutions are presented for monoenergetic, blackbody, and power-law soft photons. A comparison between the numerical and the available analytic solutions is made. 15 refs

[en] The problem of high-energy gamma rays and electrons entering an isotropic background radiation field is examined. The gamma rays produce electron-positron pairs by photon-photon interactions with the background photons, and the electrons Compton-upscatter the background photons, giving rise to a pair-photon cascade. The transition rates of Compton scattering and photon-photon pair production are calculated analytically for power-law and blackbody background radiation fields. 36 references

[en] The continuum spectra of radio-quiet active galactic nuclei, which are steeper in the near-IR and flatter in the X-ray regime, can be produced in a synchrotron self-Compton model with a broken power law electron distribution that is flat at low, and steep at large, Lorentz factor values. While the steeper part generates the IR spectrum via synchrotron process, both parts together produce the flatter X-ray spectrum via Compton scattering. The intersection of the two spectra corresponds to equipartition between the magnetic field and synchrotron photon energy densities, giving approximately the same luminosities in the synchrotron and Compton components. The photon spectra are self-consistently computed here, taking the effects of cooling, e(+)e(-) pair production, and higher order Compton scattering into account. 102 references

[en] The pair annihilation spectrum of free negatons and positons in relativistic optically thin plasma is numerically calculated. The relativistic Maxwell-Boltzmann distribution of electrons has been assumed. We approximate the resulting spectrum by an analytical function of temperature and frequency. The annihilation rate and the emissivity energy emitted per unit volume per second are given by one-dimensional integrals which were computed independently of the more complex radiation spectrum calculations. An analytical formula for the spectrum in the nonrelativistic limit is given. (author)

[en] We consider a nonthermal model for power-law X-ray and γ-ray sources. An initial, primary distribution of relativistic electrons is injected and cooled via Compton scattering of soft photons (produced either externally or by the synchrotron mechanism). The scattered photons, constituting a primary γ-ray source, produce electron-positron pairs that act as a secondary electron injection, which in turn produce a secondary photon spectrum. In contrast to the treatment of this problem presented by Bonometto and Rees in 1971 and Kazanas in 1984, we take into account pairs formed by a part of the photon spectrum optically thin to pair production. We solve self-consistently for the distribution of particles and photons, and present numerical results as well as analytical solutions to certain special cases. For the case of a delta-function primary electron injection we find that the photon spectrum in the X-ray region is well approximated by a power law, with the energy spectral index α/sub X/ lying in the relatively narrow range 0.5--0.9 as the compactness parameter L/sub X//R (where L/sub X/ is the X-ray luminosity and R is the source radius) varies over many orders of magnitude. We propose this as a possible mechanism to explain the universal X-ray spectra observed from active galactic nuclei

[en] A nonthermal model for power-law X-ray and gamma-ray sources is considered. An initial, primary distribution of relativistic electrons is injected and cooled via Compton scattering of soft photons (produced either externally or by the synchrotron mechanism). The scattered photons, constituting a primary gamma-ray source, produce electron-positron pairs that act as a secondary electron injection, which in turn produce a secondary photon spectrum. Pairs formed by a part of the photon spectrum optically thin to pair production are taken into account. The distribution of particles and photons is obtained, and numerical results as well as analytical solutions to certain special cases are presented. For the case of a delta-function primary electron injection it is found that the photon spectrum in the X-ray region is well approximated by a power law, with the energy spectral index alpha(X) lying in the relatively narrow range 0.5-0.9 as the compactness parameter L(x)/R (where L(x) is the X-ray luminosity and R is the source radius) varies over many orders of magnitude. This is proposed as a possible mechanism to explain the universal X-ray spectra observed from active galactic nuclei. 20 references

[en] Consideration is given to a model of gamma-ray burst sources based on repeated Compton scatterings of soft photons by relativistic nonthermal electrons. Relativistic electrons which are continuously produced in the source radiate the total power L supplied to them. Higher order Compton scatterings, which occur when L(soft) is much less than L make the model distinct. The spectrum having an X-ray energy index of about one results from the superposition of the spectral components from several orders of Compton scattering; the change of the slope at several hundred keV arises from the Klein-Nishina decline of the scattering cross section. 15 references

[en] Thermal Comptonization and e⁺e^- pair production in high-viscosity black-hole accretion flows are modelled. It is assumed that magnetic fields are in equipartition with the energy density of the flow and that cyclotron radiation is the major source of seed soft photons. The electrons are assumed to receive a constant fraction of the gravitational energy. We find that the resulting spectra have a constant X-ray energy spectral index, asub(x) ≅ O, for accretion rates 0.5 > approx rate of change of m > approx 20. Here rate of change of m ≡ rate of change of M c²/Lsub(E), and Lsub(E) is the Eddington luminosity. The spectra are cut off above ∼ 150 keV. Such spectra closely resemble that of the residual cosmic X-ray background (after subtraction of the contributions of the known classes of extragalactic sources) if the background originated at a redshift z ∼ 4-5. Thus, the residual cosmic background can be explained by an early population of active galaxies emitting thermal Comptonized spectra, as originally suggested by previous authors. (author)

[en] The problem of the e⁺e^- pair production by photo-photon, photon-particle, and particle-particle collisions in the black hole spherically symmetric accretion is considered. It is shown that these processes are much too slow to lead to any appreciable pair density in an optically thin accretion flow. The γγ process can play a role in an accretion flow of the optical thickness of a few. The rates of pair production in the binary particle collisions are calculated and it is shown that the ep → epe⁺e^- process is by one order of magnitude slower than ee → eee⁺e^- process. The maximum temperature of a stationary plasma with tau→0 is lower than that previously calculated by Bisnovatyi-Kogan, Zel'dvich and Sunyaev (1971). (orig.)