  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.
