RBSC-NVSS Sample. I. Radio and Optical Identifications of a Complete Sample of 1556 Bright X-Ray Sources

We cross-identified the ROSAT Bright Source Catalog (RBSC) and the NRAO VLA Sky Survey (NVSS) to construct the RBSC-NVSS sample of the brightest X-ray sources (>=0.1 counts s^-1~10^-12 ergs cm^-2 s^-1 in the 0.1-2.4 keV band) that are also radio sources (S>=2.5 mJy at 1.4 GHz) in the 7.8 sr of extragalactic sky with |b|>15^deg and δ>-40^deg. The sky density of NVSS sources is low enough that they can be reliably identified with RBSC sources having rms positional uncertainties >=10". We used the more accurate radio positions to make reliable X-ray/radio/optical identifications down to the POSS plate limits. We obtained optical spectra for many of the bright identifications lacking published redshifts. The resulting X-ray/radio sample is unique in its size (1557 objects), composition (a mixture of nearly normal galaxies, Seyfert galaxies, quasars, and clusters), and low average redshift [<z>~0.1].