Chandra Exposes the Core-collapsed Globular Cluster NGC 6397

We report results of the Chandra deep-imaging observation of the closest post-core-collapse globular cluster, NGC 6397. Some 25 sources are detected within 2' of the cluster center, of which ~20 are likely cluster members, with LX ≳ 3 × 1029 ergs s-1. The X-ray spectra suggest identifications with one quiescent low-mass X-ray binary (qLMXB) detected by the thermal emission from its neutron star (NS) and nine cataclysmic variables (CVs), eight of which are identified in our deep Hubble Space Telescope (HST) imaging survey (reported separately). Three (of 16) BY Dra main-sequence binary candidates identified in our earlier HST imaging study (Taylor et al.) are detected, of which one is indeed the counterpart of the eclipsing millisecond pulsar (MSP) as recently identified by Ferraro et al. Two other BY Dra candidates are also detected, whereas none of the probable He white dwarf (WD) binaries identified by Taylor et al. are, indicating they do not contain MSP primaries. The ratio of CVs to MSPs appears to be ~10 times greater than in 47 Tuc.