Compton reflection of gamma rays by cold electrons

Abstract

Using a Monte Carlo method an approximation was derived to the Green function for the Compton reflection of relativistic photon h nu greater than about m(e) c-sq, by cold electrons, extending previous treatments of this problem for nonrelativistic photons. In Compton reflection, an external flux of photons impinges upon a semiinfinite slab of electrons, gives a portion of its energy to the electrons (or receives energy if the electrons are hotter), and reemerges with an altered spectrum. This Green function may be used to easily calculate the emergent spectrum and albedo for any incident spectrum. Such reprocessing of gamma-rays may be astrophysically important when a source of gamma-rays coexists with a cool, nonrelativistic plasma, such as for nonthermal coronas above accretion disks, high energy emission near the surface of neutron stars, or a chaotic, tow-phase medium near the centers of active galaxies.