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Description
The Chandra X-ray Observatory has now discovered nearly 10000 X-ray point sources in the 2{deg}x0.8{deg} region around the Galactic Center. The sources are likely to be a population of accreting binaries in the Galactic Center, but little else is known of their nature. We obtained JHKs imaging of the 17'x17' region around Sgr A*, an area containing 4339 of these X-ray sources, with the ISPI camera on the Cerro Tololo Inter-American Observatory (CTIO) 4m telescope. We cross-correlate the Chandra and ISPI catalogs to find potential IR counterparts to the X-ray sources. The extreme IR source crowding in the field means that it is not possible to establish the authenticity of the matches with astrometry and photometry alone. We find 2137 IR/X-ray astrometrically matched sources: statistically, we estimate that our catalog contains 289+/-13 true matches to soft X-ray sources and 154+/-39 matches to hard X-ray sources. However, the fraction of true counterparts to candidate counterparts for hard sources is just 11%, compared to 60% for soft sources, making hard source NIR matches particularly challenging for spectroscopic follow-up. We calculate a color-magnitude diagram (CMD) for the matches to hard X-ray sources, and find regions where significant numbers of the IR matches are real. We use their CMD positions to place limits on the absolute Ks-band magnitudes of the potential NIR counterparts to hard X-ray sources. We find regions of the counterpart CMD with 9+/-3 likely Wolf-Rayet/supergiant binaries (with four spectroscopically confirmed in the literature) as well as 44+/-13 candidates that could consist of either main-sequence high mass X-ray binaries or red giants with an accreting compact companion. In order to aid spectroscopic follow-up, we sort the candidate counterpart catalog on the basis of IR and X-ray properties to determine which source characteristics increase the probability of a true match. We find a set of 98 IR matches to hard X-ray sources with reddenings consistent with GC distances which have a 45% probability of being true counterparts.
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