KINETICS OF ELECTRON-POSITRON PAIR PLASMAS USING AN ADAPTIVE MONTE-CARLO METHOD

A new algorithm for implementing the adaptive Monte Carlo method is gi ven. It is used to solve the Boltzmann equations that describe the tim e evolution of a nonequilibrium electron-positron pair plasma containi ng high-energy photons. These are coupled nonlinear integro-differenti al equations. The collision kernels for the photons as well as pairs a re evaluated for Compton scattering, pair annihilation and creation, b remsstrahlung, and Coulomb collisions. They are given as multidimensio nal integrals which are valid for all energies. For an homogeneous and isotropic plasma with no particle escape, the equilibrium solution is expressed analytically in terms of the initial conditions. For two sp ecific cases, for which the photon and the pair spectra are initially constant or have a power-law distribution within the given limits, the time evolution of the plasma is analyzed using the new method. The fi nal spectra are found to be in a good agreement with the analytical so lutions. The new algorithm is faster than the Monte Carlo scheme based on uniform sampling and more flexible than the numerical methods used in the past, which do not involve Monte Carlo sampling. It is also fo und to be very stable. Some astrophysical applications of this techniq ue are discussed.