Relativistic Electrons & Magnetic Fields in Clusters of Galaxies
  RXTE and BeppoSAX observations have yielded evidence for the presence of a secondary power-law spectral component in the spectra of several clusters of galaxies. This emission in clusters with extended regions of radio emission is likely to be by relativistic electrons that are Compton scattered by the CMB. The radio and non-thermal (NT) X-ray measurements yield the values of the volume-averaged magnetic field and electron energy density in the cluster extragalactic environment. These directly deduced quantities provide a tangible basis for the study of NT phenomena in clusters. 
Yoel Rephaeli