We report the identification of a bright hard X-ray source dominating the M31 bulge above 25 keV from a simultaneous NuSTAR-Swift observation. We find that this source is the counterpart to Swift J0042.6 4112, which was previously detected in the Swift BAT All-sky Hard X-ray Survey. This Swift BAT source had been suggested to be the combined emission from a number of point sources; our new observations have identified a single X-ray source from 0.5 to 50 keV as the counterpart for the first time. In the 0.5-10 keV band, the source had been classified as an X-ray Binary candidate in various Chandra and XMM-Newton studies; however, since it was not clearly associated with Swift J0042.6 4112, the previous E 3 {M}? ) donors at the location of this source. The best interpretation for the nature of this source is an X-ray pulsar with an intermediate-mass () donors at the location of this source. The best interpretation for the nature of this source is an X-ray pulsar with an intermediate-mass (? ) companion or a symbiotic X-ray binary. We discuss other possibilities in more detail.
