Description
Inspired by the hard X-ray emission from WD 2226-210, the central star of the Helix Nebula, we have made a systematic search for similar sources by correlating the white dwarf catalog of McCook & Sion (1999, See Cat. <III/235>) and the ROSAT Position Senstive Proportional Counter (PSPC) point-source catalog of White et al. (2000, Cat. <IX/31>). We find 76 white dwarfs coincident with X-ray sources at a high level of confidence. Among these sources, 17 show significant hard X-ray emission at energies greater than 0.5keV. Twelve of these white dwarfs with hard X-ray emission are in known binary systems, in two of which the accretion of the close companion's material onto the white dwarf produces hard X-ray emission, and in the other 10 the late-type companions' coronal activity emits hard X-rays. One apparently single white dwarf is projected near an active galactic nucleus that is responsible for the hard X-ray emission. The remaining four white dwarfs and two additional white dwarfs with hard X-ray emission appear single.
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