ChandraX‐Ray Sources in the Collapsed‐Core Globular Cluster M30 (NGC 7099)

Abstract

We report the detection of six discrete, low-luminosity (LX < 1033 ergs s-1) X-ray sources, located within 12'' of the center of the collapsed-core globular cluster M30 (NGC 7099), and a total of 13 sources within the half-mass radius, from a 50 ks Chandra ACIS-S exposure. Three sources lie within the very small upper limit of 1.9'' on the core radius. The brightest of the three core sources has a luminosity of LX(0.5-6 keV) ≈ 6 × 1032 ergs s-1 and a blackbody-like soft X-ray spectrum, which are both consistent with it being a quiescent low-mass X-ray binary (qLMXB). We have identified optical counterparts to four of the six central sources and a number of the outlying sources, using deep Hubble Space Telescope and ground-based imaging. While the two proposed counterparts that lie within the core may represent chance superpositions, the two identified central sources that lie outside of the core have X-ray and optical properties consistent with being cataclysmic variables (CVs). Two additional sources outside of the core have possible active binary counterparts. We discuss the X-ray source population of M30 in light of its collapsed-core status.