We have searched the archived , pointed ROSAT Position Sensitive Proportional Counter data for blazars by correlating the WGACAT X-ray database with several publicly available radio catalogs , restricting our candidate list to serendipitous X-ray sources with a flat radio spectrum ( \alpha _ { r } \leq 0.70 , where S _ { \nu } \propto \nu ^ { - \alpha } ) .
This makes up the Deep X-ray Radio Blazar Survey ( DXRBS ) .
Here we present new identifications and spectra for 106 sources , including 86 radio-loud quasars , 11 BL Lacertae objects , and 9 narrow-line radio galaxies .
Together with our previously published objects and already known sources , our sample now contains 298 identified objects : 234 radio-loud quasars ( 181 flat-spectrum quasars : FSRQ [ \alpha _ { r } \leq 0.50 ] and 53 steep-spectrum quasars : SSRQ ) , 36 BL Lacs , and 28 narrow-line radio galaxies .
Redshift information is available for 96 % of these .
Thus our selection technique is \sim 90 \% efficient at finding radio-loud quasars and BL Lacs .
Reaching 5 GHz radio fluxes \sim 50 mJy and 0.1 - 2.0 keV X-ray fluxes a few \times 10 ^ { -14 } erg cm ^ { -2 } s ^ { -1 } , DXRBS is the faintest and largest flat-spectrum radio sample with nearly complete ( \sim 85 \% ) identification .
We review the properties of the DXRBS blazar sample , including redshift distribution and coverage of the X-ray-radio power plane for quasars and BL Lacs .
Additionally , we touch upon the expanded multiwavelength view of blazars provided by DXRBS .
By sampling for the first time the faint end of the radio and X-ray luminosity functions , this sample will allow us to investigate the blazar phenomenon and the validity of unified schemes down to relatively low powers .