The X-ray AGN content of the Molonglo 408 MHz Survey: bulk properties of previously optically identified sources

The cross-correlation of a source list from the ROSAT All Sky Survey with the Molonglo 408 MHz Survey (MRC) yields a calalogue of 549 sources. The majority of the objects are quasars and radio galaxies with known optical counterparts, most of them detected in X-rays for the first time. More than one third of the objects are optically unidentified. In this paper we will present a discussion of the representative properties of the 337 previously optically identified active galactic nuclei (AGN). We find strong correlations between luminosities in the radio, optical, and X-ray bands which differ for quasars and radio galaxies. Several of the statistical source characteristics seem not to support simple unification schemes. However, for many objects some of their key properties like redshift, radio morphology and environmental conditions are not known yet. The fraction of X-ray detected quasars in the MRC is around 30%, higher than that of radio galaxies (less tha 8%). It is not currently known which intrinsic properties are responsible for the X-ray loudness of these radio objects. We further have evidence for a considerable number of objects being radio- and X-ray loud, but optically very faint.