2019MNRAS.483.4560Z

We report a 30 ksChandra ACIS-S survey of the globular cluster M3. Sixteen X-ray sources were detected within the half-light radius (2.3 arcmin) with L_X≳_2.3×_10³¹ erg s^–1. We used Hubble Space Telescope WFC3/UVIS and ACS/WFC images to find 10 plausible optical/UV counterparts. We fit the spectral energy distribution of the known cataclysmic variable (CV) 1E1339.8+2837 with a blue (T_eff = 2.10^+1.96_–0.58×10⁴K^, 90 per cent conf.) spectral component from an accretion disc, plus a red component (T_eff = 3.75_–0.15^+1.05×10³K^) potentially from a subgiant donor. The second brightest source (CX2) has a soft blackbody-like spectrum suggesting a quiescent low-mass X-ray binary (qLMXB) containing a neutron star. Six new counterparts have obvious UV and/or blue excesses, suggesting a CV or background active galactic nucleus (AGN) nature. Two (CX6 and CX8) have proper motions (PMs) indicating cluster membership, suggesting a CV nature. CX6 is blue in UV filters but red in V-I, which is difficult to interpret. Two CV candidates, CX7 and CX13, show blue excesses in B-V colour but were not detected in the UV. The other two CV candidates were only detected in the two UV bands (UV₂₇₅ and NUV₃₃₆), so do not have PM measurements, and may well be AGNs. One Chandra source can be confidently identified with a red straggler (a star reward of the giant branch). The observed X-ray source population of M3 appears consistent with its predicted stellar interaction rate.