GENERAL-RELATIVISTIC RADIATIVE-TRANSFER IN HOT ASTROPHYSICAL PLASMAS - A CHARACTERISTIC APPROACH

In this paper we present a characteristic method for solving the trans fer equation in differentially moving media in a curved spacetime. The method is completely general but its capabilities are exploited at be st in presence of symmetries, when the existence of conserved quantiti es allows us to derive analytical expressions for the photon trajector ies in phase space. In spherically symmetric, stationary configuration s, the solution of the transfer problem is reduced to the integration of a single ordinary differential equation along the bi-parametric fam ily of characteristic rays. Accurate expressions for the radiative pro cesses relevant to continuum transfer in a hot astrophysical plasma ha ve been used in evaluating the source term, including relativistic e-p , e-e bremsstrahlung and Compton scattering. A numerical code for the solution of the transfer problem in moving media in a Schwarzschild sp acetime has been developed and tested. Some applications, concerning ' 'hot'' and ''cold'' accretion onto nonrotating black holes as well as static atmospheres around neutron stars, are presented and discussed.