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arXiv · 1311.1821

Around 200 new X-ray binary IDs from 13 years of Chandra observations of the M31 center

R. Barnard·M. R. Garcia·F. Primini·Z. Li·F. Baganoff·S. S. Murray
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Abstract

We have created 0.3--10 keV, 13 year, unabsorbed luminosity lightcurves for 528 X-ray sources in the central 20' of M31. We have 174 Chandra observations spaced at ~1 month intervals thanks to our transient monitoring program, deeper observations of the M31 nucleus, and some public data from other surveys. We created 0.5--4.5 keV structure functions (SFs) for each source, for comparison with the ensemble structure function of AGN. We find 220 X-ray sources with luminosities > ~1E+35 erg/s that have SFs with significantly more variability than the ensemble AGN SF, and are likely X-ray binaries (XBs). A further 30 X-ray sources were identified as XBs using other methods. We therefore have 250 probable XBs in total, including ~200 new identifications. This result represents great progress over the ~50 XBs and ~40 XB candidates previously identified out of the ~2000 X-ray sources within the D_25 region of M31; it also demonstrates the power of SF analysis for identifying XBs in external galaxies. We also identify a new transient black hole candidate, associated with the M31 globular cluster B128.

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R. Barnard, M. R. Garcia, F. Primini, Z. Li, F. Baganoff, S. S. Murray. 2013-11-07. Around 200 new X-ray binary IDs from 13 years of Chandra observations of the M31 center. https://doi.org/10.1088/0004-637x%2F780%2F1%2F83

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