The CfA Einstein Observatory extended deep X-ray survey

Abstract

In this paper, we present the results of X-ray analysis and optical identifications for the Einstein Observatory Extended Deep X-Ray Survey. The survey contains 10 IPC exposures and 34 HRI exposures. Using the IPC as our primary instrument for source detection and count rate determination, we construct a signal-to-noise limited sample covering ~ 2.3 deg^2^, with a typical limiting sensitivity of ~ 5 x 10^14^ ergs cm^-2^ s^-1^ in the energy range 0.8-3.5 keV. We detect 25 IPC sources at or above a count rate signal-to-noise threshold of 4.5. Eighteen are detected independently in the HRI, leading to the identification of six with stars and 11 with extragalactic objects. The remaining sources are classified as extragalactic on the basis of the ratio of X-ray to optical flux. The population of identified extragalactic objects is dominated by QSOs. Although the content of the survey sample has changed somewhat, the basic conclusions of the original survey remain unaffected. The extragalactic log N-log S relationship at our flux limit is consistent with that derived from samples at higher flux levels although the relative contribution of different classes of extragalactic objects has changed. We estimate that ~ 16%-25% of the XRB is due to discrete sources above our flux limit alone.