The ROSAT North Ecliptic Pole Survey: The X-Ray Catalog

The sky around the north ecliptic pole (NEP), at α(J2000.0) = 18h00m00s, δ(J2000.0) = +66°33′39′′, has the deepest exposure of the entire ROSAT All-Sky Survey (RASS). The NEP is an undistinguished region of moderate Galactic latitude, b = 29.°8, and hence suitable for compiling statistical samples of both Galactic and extragalactic objects. We have made such a compilation in the 80.6 deg2 region surrounding the NEP. Our sample fully exploits the properties of the RASS, since the only criteria for inclusion are source position and significance, and it yields the deepest large solid angle contiguous sample of X-ray sources to date. We find 442 unique sources above a flux limit ~2 × 10-14 ergs cm-2 s-1 in the 0.5-2.0 keV band. In this paper we present the X-ray properties of these sources as determined from the RASS. These include positions, fluxes, spectral information in the form of hardness ratios, and angular sizes. Since we have performed a comprehensive optical identification program we also present the average X-ray properties of classes of objects typical of the X-ray sky at these flux levels. We discuss the use of the RASS to find clusters of galaxies based on their X-ray properties alone.