A SURVEY OF THE EINSTEIN IPC DATABASE FOR EXTENDED X-RAY SOURCES

We present the results of a new analysis of the entire set of data col lected by the Imaging Proportional Counter (IPC) on board the Einstein Observatory. Our survey is distinct from previous work such as the Ei nstein Extended Medium Sensitivity Survey (EMSS) in that it is designe d to find extended sources and diffuse emission rather than point sour ces. In addition, the source detection algorithm is substantially impr oved over that used for the EMSS. We have searched for sources using c ircular apertures with variable radii up to 6.10'. We have constructed criteria to ascertain which of the detections are truly diffuse and w hich of the sizes best approximates each detection. Using these criter ia we have produced a catalog of 1326 extended source candidates at hi gh Galactic latitude (\b\>20 deg). Cross-correlating this Bst with exi sting source catalogs yields a reasonably comprehensive identification of the sources in our list. We find that over 400 are identified with known clusters of galaxies. Other objects are identified with galaxie s, supernova remnants, AGN, and stars; the first two categories are of ten truly extended objects, while the latter two sets of objects can a ppear extended as a consequence of their soft X-ray spectra coupled wi th the broad point spread function of the IPC at low energies. A total of 321 extended sources remain unidentified. Many of these may be her etofore uncataloged clusters and groups of galaxies at moderate redshi fts. (C) 1997 American Astronomical Society.