Abstract
We report the results of a search for hard X-ray binaries (HXRBs) among previously unidentified sources from ROSAT PSPC pointed observations, using the automated X-ray source classifier ClassX. Twice as many new candidate HXRBs are found as are already known. The new HXRBs are, on average, fainter and have softer X-ray spectra than the previously known objects. The majority of the new HXRBs are located within 2° of the Galactic plane, with substantial concentration within 20° of longitude about the Galactic center. Their large number in the Galactic disk, the lack of association with Galactic globular clusters, and the presence of some of them in the field of nearby regions of star formation allows one to speculate that many of them are low-mass X-ray binaries (LMXRBs) associated with young stars. Some resemble wind-accreting neutron stars. The new ClassX HXRBs also provide support for recent models of formation and evolution of LMXRBs that involve intermediate-mass secondary stars in XRB progenitor systems.
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