1997A&A...319..413B

We present a sample of 654 radio quasars seen in the ROSAT All-Sky Survey and the ROSAT point source catalogue and study their broad band properties. The size of this list allows a statistically significant investigation of the soft X-ray properties of various subgroups distinguished by their radio properties. It is found that flat spectrum and steep spectrum quasars have slightly different X-ray properties which can be understood in the frame of a two component model for the emission: a beamed flat spectral component which is more dominant in flat radio spectrum objects and a steep more isotropic soft component. Combinations of these two components lead to the observed correlations of the X-ray spectral slope with the radio spectral properties, with the core dominance and radio loudness of the objects, and with redshift. Various correlations exist between the radio, optical, and X-ray properties of the sources. Flat spectrum quasars are X-ray louder than steep spectrum objects, the X-ray loudness does not evolve with redshift, and the apparent dependence of α_ox on the optical luminosity seems to be due to biases inherent to the data. Simple proportionalities between the luminosities in the different wavelength bands appear to be inappropriate descriptions of the actual physical situation as they do not account for the varying contributions of the core and extended emission in the objects, i.e., the relative fraction of the beamed core to the unbeamed extended radio emission. Both components contribute in all energy bands but the physical processes governing these complex relations are not yet understood. Finally, redshift dependencies and selection effects influence the correlations as well, leading to deviations from a simple linear relation between the measured quantities in many cases .