A LARGE-PARTICLE MONTE-CARLO CODE FOR SIMULATING NONLINEAR HIGH-ENERGY PROCESSES NEAR COMPACT OBJECTS

High-energy radiation processes in compact cosmic objects are often ex pected to have a strongly non-linear behaviour. Such behaviour is show n, for example, by electron-positron pair cascades and the time evolut ion of relativistic proton distributions in dense radiation fields. Th ree independent techniques have been developed to simulate these non-l inear problems: the kinetic equation approach; the phase-space density (PSD) Monte Carlo method; and the large-particle (LP) Monte Carlo met hod. In this paper, we present the latest version of the LP method and compare it with the other methods. The efficiency of the method in tr eating geometrically complex problems is illustrated by showing result s of simulations of 1D, 2D and 3D systems. The method is shown to be p owerful enough to treat non-spherical geometries, including such effec ts as bulk motion of the background plasma, reflection of radiation fr om cold matter, and anisotropic distributions of radiating particles. It can therefore be applied to simulate high-energy processes in such astrophysical systems as accretion discs with coronae, relativistic je ts, pulsar magnetospheres and gamma-ray bursts.