Angle-dependent Compton reflection of X-rays and gamma-rays
Pawel Magdziarz
Astronomical Observatory, Jagiellonian University, Orla 171, 30-244
Cracow, Poland, Internet: pavel@oa.uj.edu.pl
A. A. Zdziarski
Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland,
Internet: aaz@camk.edu.pl
Using a Monte Carlo method, we derive approximations to Green's
functions for the Compton reflection of X-rays and \g-rays by
cold electrons. In Compton reflection, X-rays and \g-rays emitted
by a source impinge upon a slab (e.g. an accretion disc) and re-emerge
with a spectrum altered by Compton scattering and bound-free absorption.
The obtained Green's functions are dependent on the viewing angle
of the reflecting slab, which extends the previous treatments
of the problem, in which the reflected spectra were integrated
over all viewing angles. The dependence on the viewing angle is
especially important in hard X-rays and soft \g-rays, in which
regime the reflected spectrum strongly hardens with increasing
viewing angle. This is an important effect for modelling \g-ray
spectra of active galactic nuclei and Galactic black hole candidates,
where the presence of Compton reflection has been established
before from X-ray data.