Results from the cross-correlation of the ROSAT All Sky Survey source catalog with the 87GB 5 GHz survey

Abstract

We cross-correlated the point source catalog obtained from the ROSAT All Sky Survey with a catalog generated from the Green Bank 5 GHz survey. This resulted in a list of 2127 objects, which represents the largest and least biased sample of radio loud X-ray sources so far. Using information from astronomical databases and from recently initiated optical identification programs, we were able to find extragalactic optical counterparts for 617 of these sources. Thus more than two thirds of the objects remain to be identified. The radio, optical and X-ray luminosities of the identified sources are strongly correlated, with galaxies and quasars showing different regression slopes. We estimated the soft X-ray spectral indices of all objects, utilizing a hardness ratio technique. In general, galaxies tend to have a harder soft X-ray continuum when compared to quasars. BL Lac objects have rather steep spectra on average, similar to the large group of unidentified objects. In order to obtain accurate positions for optical identification programs and to determine high resolution core fluxes, all sources were re-observed with the VLA at 5 GHz. Follow-up observations at Effelsberg provide quasi-simultaneous radio spectra for the brighter (>100mJy) objects. Given the quality and the quantity of the data, this sample should provide strong tests for currently discussed unification schemes of radio-loud AGN.