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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° and δ > -40°. 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].