@article {23912,
	title = {New XMM-Newton Analysis of Three Bright X-Ray Sources in M31 Globular Clusters, Including a New Black Hole Candidate},
	volume = {689},
	year = {2008},
	month = {2008/12/1},
	pages = {1215 - 1221},
	abstract = {We present a 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 light curve was seen to vary by ~10\%, and its 0.3-7.0 keV emission spectrum was well described by an absorbed power law with photon index 1.44 +/- 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 behavior is typically observed at luminosities lesssim10\% Eddington. However, XBo 45 exhibited this behavior at an unabsorbed, 0.3-10 keV luminosity of 2.5 +/- 0.2 {\texttimes} 10<SUP>38</SUP> erg s<SUP>-1</SUP>, or ~140\% Eddington for a 1.4 M<SUB>⊙</SUB> 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 ~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 a neutron star.},
	keywords = {Astrophysics, galaxies: individual: M31, methods: data analysis, X-rays: binaries},
	isbn = {0004-637X},
	url = {https://ui.adsabs.harvard.edu/abs/2008ApJ...689.1215B},
	author = {Barnard, R. and Stiele, H. and Hatzidimitriou, D. and Kong, A. K. H. and Williams, B. F. and Pietsch, W. and Kolb, U. C. and Haberl, F. and Sala, G.}
}
