Collective spectra of resonant inverse Compton scattering of fast electrons in a varied magnetic field

Abstract

The resonant inverse Compton scattering (RICS) of the relativistic electrons in an intense magnetic field of a neutron star is an efficient mechanism for producing high-energy gamma-rays. For the purpose of practical applications of RICS, in this paper, we present a basic formula of the collective RICS spectrum produced by a population of relativistic electrons moving outwards along the directions of the magnetic and near-magnetic axes of a strongly magnetized neutron star or strange star. The derivation of the formula is based on a simple semiclassical quantum expression, describing the RICS spectral power of a single fast electron in a subcritical field B < B-cr = 4.413 x 10(13) G, given in our previous paper. As examples of application, by using this new formula, we calculated the collective RICS spectra in some typical ambient soft-photon fields around the neutron star. The obtained collective RICS spectra have simple analytical forms, which are convenient to compare with the observed spectra. Our calculations show that the RICS process is really a very efficient radiation mechanism in the hard X-ray and gamma-ray bands if the 'accommodation condition', presented in our previous paper, is satisfied. We show that the broken power-law form (different power indices in low- and high-frequency bands) is a common and proper feature of various collective RICS spectra, despite the initial forms of the ambient soft-photon field. Finally, we discuss the possible applications in high-energy astrophysics, e.g. in the exploration of the origins of radiation in the gamma-ray bursts (GRBs) and gamma-ray pulsars (GRPs), etc.