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R. E. Rutledge, T. A. Prince, R. Brunner (Caltech)
We quantitatively cross-associate the 18811 ROSAT Bright Source Catalog (RASS/BSC) X-ray sources with optical sources in the USNO-A2 catalog, calculating the probability of unique association (Pid) with each candidate optical source within 75 arc sec of the X-ray source position, on the basis of optical magnitude and proximity. We present catalogs of RASS/BSC sources for which Pid>98%, Pid>90%, and Pid>50%, which contain 2705, 5492, and 11303 unique USNO A-2 optical associations, respectively, down to the stated level of significance. We include in this catalog a list of objects in the SIMBAD database within 10 arc sec of the USNO-A2 position, as an aid to identification and source classification. This is the first RASS/BSC counterpart catalog which provides a probability of association for each X-ray/optical association, quantifying the certainty of each individual association.
This work is funded partially by NSF Cooperative Agreement ACI-96-19020.