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We have previously identified 10 M31 black hole candidates (BHCs) in M31,from their X-ray properties alone. They exhibit "hard state" emission spectrathat are seen at luminosities < ~10% Eddington in X-ray binaries (XBs)containing a neutron star (NS) or black hole (BH), at luminosities thatsignificantly exceed the NS threshold. Nine of these are associated withglobular clusters (GCs); hence, these are most likely low mass X-ray binaries(LMXBs); eight are included in this survey. We have recently discovered thatanalysis of the long term 0.5--4.5 keV variability of XBs via structurefunctions allows us to separate XBs from AGN, even though the emission spectraare often similar; this has enabled us to search for BHCs outside of GCs. Wehave identified 26 new BHCs (12 strong, 14 plausible) within 20' of the M31nucleus (M31*), using 152 Chandra observations spaced over ~13 years; some ofour classifications were enhanced with XMM-Newton observations. Of these, 7appear within 100" of M31*; this supports the theory suggesting that thisregion experiences enhanced XB production via dynamical processes similar tothose seen in GCs. We have found a parameter space where our black holecandidates are separated from Galactic neutron star binaries: we show thatmodelling a simulated hard state spectrum with a disk blackbody + blackbodymodel yields parameters that lie outside the space occupied by neutron starbinaries that are modeled this way. The probability that our BHCs all liewithin the NS parameter space is ~3E-29.

Chandra identification of 26 new black hole candidates in the central region of M31