ON THE SOFT-X-RAY SPECTRA OF GAMMA-LOUD BLAZARS

ROSAT observations of a large sample of bright gamma-ray (E > 100 MeV) blazars are presented. Results of a detailed spectral analysis in the soft approximately 0.1-2.0 keV energy range are discussed in relation to the overall energy distribution with particular emphasis on the re lation between X-ray and gamma-ray properties. A significant anticorre lation between X-ray and gamma-ray spectral shapes of flat-spectrum ra dio quasars (FSRQs) and BL Lac objects has been discovered. A differen t shape in the overall energy distributions from radio to gamma-ray en ergies between FSRQs and BL Lac objects is also implied by the correla tion of their broadband spectral indices alpha(ro) and alpha(x gamma). Both the above correlations can be explained if both the infrared to ultraviolet emission and the hard X-ray to gamma-ray emission originat e from the same electron population, via, respectively, the synchrotro n process and the inverse Compton mechanism. We suggest that a key par ameter for understanding the overall energy distributions of both clas ses of objects is the energy at which the synchrotron emission peaks i n a nu-nu F(nu) representation.