SELF-CONSISTENT FOKKER-PLANCK TREATMENT OF PARTICLE DISTRIBUTIONS IN ASTROPHYSICAL PLASMAS

High-energy, multicomponent plasmas in which pair creation and annihil ation, lepton-lepton scattering, lepton-proton scattering, and Compton ization all contribute to establishing the particle and photon distrib utions are present in a broad range of compact astrophysical objects. The different constituents are often not in equilibrium with each othe r, and this mixture of interacting particles and radiation can produce substantial deviations from a Maxwellian profile for the lepton distr ibutions. Earlier work has included much of the microphysics needed to account for electron-photon and electron-proton interactions, but lit tle has been done to handle the redistribution of the particles as a r esult of their Coulomb interaction with themselves. The most detailed analysis thus far for finding the exact electron distribution appears to have been done within the framework of nonthermal models, where the electron distribution is approximated as a thermal one at low energy with a nonthermal tail at higher energy. Recent attention, however, ha s been focused on thermal models. Our goal here is to use a Fokker-Pla nck approach in order to develop a fully self-consistent theory for th e interaction of arbitrarily distributed particles and radiation to ar rive at an accurate representation of the high-energy plasma in these sources. We derive Fokker-Planck coefficients for an arbitrary electro n distribution and correct an earlier expression for the diffusion coe fficient used by previous authors. We conduct several tests representa tive of two dominant segments of parameter space. For high source comp actness of the total radiation field, l similar to 10(2), we find that although the electron distribution deviates substantially from a Maxw ellian, the resulting photon spectra are insensitive to the shape of t he exact electron distribution, in accordance with some earlier result s. For low source compactness, l similar to few, and an optical depth less than or similar to 0.2, however, we find that both the electron d istribution and the photon spectra differ strongly from what they woul d be in the case of a Maxwellian distribution. In addition, for all va lues of compactness, we find that different electron distributions lea d to different positron number densities and proton equilibrium temper atures. This means that the ratio of radiation pressure to proton pres sure is strongly dependent on the lepton distribution, which might lea d to different configurations of hydrostatic equilibrium. This, in tur n, may change the compactness, optical depth, and heating and cooling rates and therefore lead to an additional change in the spectrum. An i mportant result of our analysis is the derivation of useful, approxima te analytical forms for the electron distribution in the case of stron gly non-Maxwellian plasmas.