DISCOVERY OF A HARD X-RAY SOURCE, SAX J0635+0533, IN THE ERROR BOX OF THE GAMMA-RAY SOURCE 2EG 0635 +0521

摘要

We have discovered an X-ray source, SAX J0635 +0533, with a hard spectrum within the error box of the GeV gamma-ray source in Monoceros, 2EG J0635 +0521. The unabsorbed fiux from the source is l.2 x 10~(-11) ergs cm~(-2) s~(-1) in the 2-10 keV band. The X-ray spectrum is consistent with a simple power- law model with absorption. The photon index is l.50 +- 0.08, and we detect emission out to 40 keV. Optical observations identify a counterpart with a V magnitude of 12.8. The counterpart has broad emission lines and the colors of an early B-type star. If the identification of the X-ray/optical source with the gamma-ray source is correct, then the source would be a gamma-ray-emitting X-ray binary.