The Deep X-ray Radio Blazar Survey (DXRBS) - II. New identifications

We have searched the archived, pointed ROSAT Position Sensitive Proportiona l Counter data for blazars by correlating the WGACAT X-ray data base with s everal publicly available radio catalogues, restricting our candidate list to serendipitous X-ray sources with a flat radio spectrum (alpha (r) less t han or equal to 0.70, where S-nu proportional to nu (-alpha)). This makes u p the Deep X-ray Radio Blazar Survey (DXRBS), Here we present new identific ations and spectra for 106 sources, including 86 radio-loud quasars, 11 BL Lacertae objects, and nine narrow-line radio galaxies. Together with our pr eviously published objects and already-known sources, our sample now contai ns 298 identified objects: 234 radio-loud quasars [181 flat-spectrum quasar s: FSRQ (alpha (r) less than or equal to 0.50) and 53 steep-spectrum quasar s: SSRQ], 36 BL Lacs and 28 narrow-line radio galaxies. Redshift informatio n is available for 96 per cent of these. Thus our selection technique is si milar to 90 per cent efficient at finding radio-loud quasars and BL Lacs. R eaching 5-GHz radio fluxes similar to 50mJy and 0.1-2.0 keV X-ray fluxes a few x 10(-14) erg cm(-2) s(-1), DXRBS is the faintest and largest flat-spec trum radio sample with nearly complete (similar to 85 per cent) identificat ion. We review the properties of the DXRBS blazar sample, including redshif t distribution and coverage of the X-ray-radio-power plane for quasars and BL Lacs. Additionally, we touch upon the expanded multiwavelength view of b lazars provided by DXRBS. By sampling for the first time the faint end of t he radio and X-ray luminosity functions, this sample will allow us to inves tigate the blazar phenomenon and the validity of unified schemes down to re latively low powers.