We present detailed analysis of three globular cluster X-ray sources in the XMM-Newton extended survey of M31 .
The X-ray counterpart to the M31 globular cluster Bo 45 ( XBo 45 ) was observed with XMM-Newton on 2006 December 26 .
Its combined pn+MOS 0.3–10 keV lightcurve was seen to vary by \sim 10 % , and its 0.3–7.0 keV emission spectrum was well described by an absorbed power law with photon index 1.44 \pm 0.12 .
Its variability and emission is characteristic of low mass X-ray binaries ( LMXBs ) in the low-hard state , whether the accretor is a neutron star or black hole .
Such behaviour is typically observed at luminosities \lesssim 10 % Eddington .
However , XBo 45 exhibited this behaviour at an unabsorbed , 0.3–10 keV luminosity of 2.5 \pm 0.2 \times 10 ^ { 38 } erg s ^ { -1 } , or \sim 140 % Eddington for a 1.4 M _ { \odot } neutron star accreting hydrogen .
Hence , we identify XBo 45 as a new candidate black hole LMXB .
XBo 45 appears to have been consistently bright for \sim 30 years , consistent with theoretical prediction for a globular cluster black hole binary formed via tidal capture .
Bo 375 was observed in the 2007 , January 2 XMM-Newton observation , and has a two-component spectrum that is typical for a bright neutron star LMXB .
Bo 135 was observed in the same field as Bo 45 , and could contain either a black hole or neutron star .