We report a 30 ~ { } \mathrm { ks } Chandra ACIS-S survey of the globular cluster M3 .
Sixteen X-ray sources were detected within the half-light radius ( 2.3 ^ { \prime } ) with L _ { X } \gtrsim 2.3 \times 10 ^ { 31 } ~ { } \mathrm { 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 1E1339.8+2837 with a blue ( T _ { \mathrm { eff } } = 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 { eff } } = 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 { UV _ { 275 } } and \mathrm { NUV _ { 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 .