Optical identification of multiple faint X-ray sources in the globular cluster NGC 6752: Evidence for numerous cataclysmic variables

We report on the Chandra X-Ray Observatory ACIS-S3 imaging observation of the globular cluster NGC 6752. We detect six X-ray sources within the 10″.5 core radius and 13 more within the 115″ half-mass radius down to a limiting luminosity of L_X ≈ 10³⁰ ergs s ^-1 for cluster sources. We reanalyze archival data from the Hubble Space Telescope and the Australia Telescope Compact Array and make 12 optical identifications and one radio identification. Based on X-ray and optical properties of the identifications, we find 10 likely cataclysmic variables (CVs), one to three likely RS CVn or BY Dra systems, and one or two possible background objects. Of the seven sources for which no optical identifications were made, we expect that approximately two to four are background objects and that the rest are either CVs or some or all of the five millisecond pulsars whose radio positions are not yet accurately known. These and other Chandra results on globular clusters indicate that the dozens of CVs per cluster expected by theoretical arguments are being found. The findings to date also suggest that the ratio of CVs to other types of X-ray sources is remarkably similar in clusters of very different structural parameters.