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].