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 (greater than or equal to0.1 counts s(-1)similar to 10(-12) ergs cm(-2) s(-1) in the 0.1-2.4 keV band) that are also radio sources (S greater than or equal to 2.5 mJy at 1.4 GHz) in the 7.8 sr of extragalactic sky with \b\ > 15 degrees and delta > -40 degrees. The sky density of NVSS sources is low enough that they can be reliably identified with RBSC sources having rms positional uncertainties greater than or equal to 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] similar to 0.1].