Identifications of Faint Chandra Sources in the Globular Cluster M3

We report a $30\mathrm{k}\mathrm{s}$ $Chandra$ ACIS-S survey of the globular cluster M3. Sixteen X-ray sources were detected within the half-light radius (${2.3}^{\mathrm{\prime }}$) with $L_X\gtrsim 2.3\times {10}^{31}\mathrm{e}\mathrm{r}\mathrm{g}{\mathrm{s}}^{-1}$. We used $HubbleSpaceTelescope$ WFC3/UVIS and ACS/WFC images to find 10 plausible optical/UV counterparts. We fit the spectral energy distribution of the known cataclysmic variable 1E1339.8+2837 with a blue ($T_$\mathrm{e}\mathrm{f}\mathrm{f}$ = 2.10^{+1.96}{-0.58}\times 10^4~$\mathrm{K}$$, 90% conf.) spectral component from an accretion disc, plus a red component ($T$\mathrm{e}\mathrm{f}\mathrm{f}$ = 3.75_{-0.15}^{+1.05}\times 10^3~$\mathrm{K}$$) 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 cataclysmic variable (CV) or background active galactic nucleus (AGN) nature. Two (CX6 and CX8) have proper motions 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 ($\mathrm{U}{\mathrm{V}}_{275}$ and $\mathrm{N}\mathrm{U}{\mathrm{V}}_{336}$), so do not have proper motion measurements, and may well be AGNs. One $Chandra$ source can be confidently identified with a red straggler (a star redward of the giant branch). The observed X-ray source population of M3 appears consistent with its predicted stellar interaction rate.