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

摘要

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 (MV ~ 4.7), suggested by Deutsch and coworkers as the optical candidate for the LMXB, is identified (03) not with the LMXB, but with another, newly detected source (B). Using archival Hubble Space Telescope (HST) images, we identify (03) the LMXB (A) and one of the remaining new sources (C) with blue variable optical counterparts at MV ~ 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 NH = 5.5 × 1020, source A has intrinsic luminosity LX ~ 5.3 × 1035 ergs s-1. Assuming a 1 keV thermal bremsstrahlung spectrum, B has LX ~ 4.1 × 1033 ergs s-1, while C and D have LX ~ 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.