Time-dependent numerical model for the emission of radiation from relativistic plasma

We describe a numerical model constructed for the study of the emission of radiation from relativistic plasma under conditions characteristic of, e.g., gamma-ray bursts and active galactic nuclei. The model solves self-consistently the kinetic equations for e^± and photons, describing cyclosynchrotron emission, direct Compton and inverse Compton scattering, and pair production and annihilation, including the evolution of high-energy electromagnetic cascades. The code allows calculations over a wide range of particle energies, spanning more than 15 orders of magnitude in energy and timescales. Our unique algorithm, which enables to follow the particle distributions over a wide energy range, allows us to accurately derive spectra at high energies, >100 TeV. We present the kinetic equations that are being solved, a detailed description of the equations describing the various physical processes, the solution method, and several examples of numerical results. Excellent agreement with analytical results of the synchrotron-synchrotron self-Compton model is found for parameter-space regions in which this approximation is valid, and several examples are presented of calculations for parameter-space regions for which analytic results are not available.