On the non-thermal high energy radiation of galaxy clusters

Abstract

The origin of the nonthermal EUV and hard X-ray emission "excess" reported from some galaxy clusters has been intensively debated over last several years. The most favored models which refer this excess to relativistic electrons upscattering the 2.7 K CMBR generally requires very low magnetic field, significantly below the estimates derived from the Faraday Rotation Measurements, unless one invokes rather nonstandard assumptions concerning the energy and pitch angle distributions of nonthermal electrons. In this paper we suggest a new model assuming that the "nonthermal" excess is due to synchrotron radiation of ultrarelativistic (multi-TeV) electrons of "photonic" origin. These electrons are continuously introduced throughout the entire intracluster medium by very high energy (hypothetical) gamma-rays through interactions with the diffuse extragalactic radiation fields. We present numerical calculations for the Coma cluster, and briefly discuss implications of the model for other galaxy clusters both in the X- and gamma-ray energy domains.