A Catalog of 203 Galaxy Clusters Serendipitously Detected in theROSATPSPC Pointed Observations

We present a catalog of 200 clusters of galaxies serendipitously detected in 647 ROSAT PSPC pointings covering 158 square degrees. This is one of the largest X-ray selected cluster samples, comparable in size only to the ROSAT All-Sky Survey sample of nearby clusters (Ebeling et al. 1997). We detect clusters in the inner 17. 5 arcmin of the ROSAT PSPC field of view using the spatial extent of their X-ray emission. Cluster X-ray luminosities range from 10⁴2 erg/s to ~5x10⁴4 erg/s, i. e. from poor groups to rich clusters. The cluster redshifts range from z=0. 015 to z>0. 5. The catalog lists X-ray fluxes, core-radii, spectroscopic redshifts for 73 clusters and photometric redshifts for the remainder. We have optically confirmed 200 of 223 X-ray sources as clusters of galaxies. Of the remaining 23 sources, 18 are likely false detections arising from blends of unresolved point X-ray sources, and for 5 we have not obtained deep CCD images. Above a flux of 2e-13 erg/s/cm**2, 98\% of extended X-ray sources are optically confirmed clusters. The log N-log S relation derived from our catalog shows excellent agreement with previous results: EMSS and ROSAT All-Sky survey BCS in teh bright end and WARPS at intermediate fluxes. Our cluster counts appear to be systematically higher than those from a 50 deg² survey of Rosati et al. (1998). In particular, at a flux of 2e-13 erg/s/cm**2, we find a surface density of clusters of 0. 57+/-0. 07 per square degree, which is a factor of 1. 3 more than found by Rosati et al. This difference is marginally significant at the ~2 sigma level. The large area of our survey makes it possible to study the evolution of the X-ray luminosity function in the high luminosity range inaccessible with other, smaller area ROSAT surveys.