RADIO-LOUD ACTIVE GALAXIES IN THE NORTHERN ROSAT ALL-SKY SURVEY : II. MULTI-FREQUENCY PROPERTIES OF UNIDENTIFIED SOURCES

We present the broad band, radio - to - X-ray, prop- erties of a large sample of mostly previously optically unidenti- ed radio-loud X-ray sources from the correlation of a ROSAT All-Sky Survey source list with the 5 GHz Green Bank Survey of the northern sky (RGB sample) which is one of the largest well-dened flux-limited surveys of AGN ever obtained. Fur- ther, the RGB pushes 1-2 orders of magnitude deeper in both X-ray and radio flux compared to previous unbiased wide-area AGN surveys. Follow up VLA observations of the candidate objects yielded positions with arcsec accuracy which were used to nd optical counterparts to the sources from digitized POSS plates. The sources are divided into three classes according to the po- sitional offset between the X-ray and radio candidates and the spatial resolution of the radio observations, reflecting the vari- ous degrees of condence about the correctness of the proposed association. Although the nature of the sources as well as their redshifts remain to be determined in spectroscopic follow up observa- tions, the derived flux ratios lead to the conclusion that the ma- jority of them are quasars. Hardly any correlations could be found between different source parameters, possibly due to the fact that most of the objects are found in a relatively small flux range near the sensitivity limit of the radio catalogue. The majority of the new RGB sources have broad-band properties between those of traditional radio-selected and X- ray selected AGN. There is no bimodal distribution in the radio- loudnessdistribution,andthetraditionaldivisionbetweenradio- quiet and radio-loud AGN may not be warranted