AROUND 200 NEW X-RAY BINARY IDs FROM 13 YR OF CHANDRA OBSERVATIONS OF THE M31 CENTER

Abstract

We have created 0.3-10 keV, 13 yr, unabsorbed luminosity lightcurves for 528 X-ray sources in the central 20' of M31. We have 174 Chandra observations spaced at ~1 month intervals due 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 SF of active galactic nuclei (AGN). We find 220 X-ray sources with luminosities [> over ~]10[superscript 35] erg s[superscript –1] that have SFs with significantly more variability than the ensemble AGN SF, and which 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 [subscript 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.