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 relation between X-ray and gamma-ray properties. A significant anticorrelation between X-ray and gamma-ray spectral shapes of flat-spectrum radio quasars (FSRQs) and BL Lac objects has been discovered. A different shape in the overall energy distributions from radio to gamma-ray energies between FSRQs and BL Lac objects is also implied by the correlation 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 originate from the same electron population, via, respectively, the synchrotron process and the inverse Compton mechanism. We suggest that a key parameter for understanding the overall energy distributions of both classes of objects is the energy at which the synchrotron emission peaks in a nu-nu F(nu) representation.