Identification of the Low-Mass X-Ray Binary and Faint X-Ray Sources in NGC 6652

Abstract

We have detected three new X-ray point sources, in addition to the known low-mass X-ray binary (LMXB) X1832-330, in the globular cluster NGC 6652 with a Chandra 1.6 ks HRC-I exposure. Star 49 (M_V~4.7), suggested by Deutsch and coworkers as the optical candidate for the LMXB, is identified (<0.3") not with the LMXB, but with another, newly detected source (B). Using archival Hubble Space Telescope (HST) images, we identify (<0.3") the LMXB (A) and one of the remaining new sources (C) with blue variable optical counterparts at M_V~3.7 and 5.3, respectively. The other new source (D) remains unidentified in the crowded cluster core. In the 0.5-2.5 keV range, assuming a 5 keV thermal bremsstrahlung spectrum and N_H=5.5×10²⁰, source A has intrinsic luminosity L_X~5.3×10³⁵ ergs s^-1. Assuming a 1 keV thermal bremsstrahlung spectrum, B has L_X~4.1×10³³ ergs s^-1, while C and D have L_X~8×10³² ergs s^-1. Source B is probably a quiescent LMXB, while source C may be either a luminous cataclysmic variable or a quiescent LMXB.