A study of the population of LMXBs in the bulge of M31

Abstract

The purpose of this study is to explore the population of X-ray point sources in the bulge of M31, with the primary goal to contrast properties of various subpopulations, such as persistent and transient sources, primordial LMXBs and dynamically formed ones. Based on the data from 26 archival Chandra observations we study the source content and properties of various subpopulations of X-ray sources to a maximum distance of 12 arcmin from the centre of M31. A study of the spatial distribution and the luminosity function of the X-ray sources shows that the distribution of primordial LMXBs is consistent with the distribution of the K-band light and that their luminosity function flattens below ~10^{37} erg/s to the dN/dL proportional to 1/L law in agreement with the behaviour found earlier for LMXBs in the Milky Way and in Cen A. The luminosity function of dynamically formed LMXBs shows a prominent fall-off below log(L_X)<36.5. Although the statistics is insufficient to claim a genuine low-luminosity cut-off in the luminosity function, the best fit powerlaw with a slope of -0.6+-0.2 is significantly flatter than the dN/dL proportional to 1/L law. We found 28 transient X-ray sources. Their spatial distribution follows the distribution of the persistent LMXBs within the accuracy allowed by the limited number of transients.

15 pages, accepted for publication in A&A revised version includes a comparison of the LF of LMXBs in globular clusters in M31 and in the Galaxy

Cited by in corpus (12)

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• Unresolved emission and ionized gas in the bulge of M31
• The dynamical formation of LMXBs in dense stellar environments: globular clusters and the inner bulge of M31
• Low-mass X-ray binaries in the bulge of the Milky Way
• Chandra detection of diffuse hot gas in and around the M31 bulge
• Luminosity functions of LMXBs in Centaurus A: globular clusters versus the field
• On the detection of the progenitor of the type Ia supernova 2007on
• Time variability of X-ray sources in the M 31 centre field
• XMM-Newton discovery of 217 s pulsations in the brightest persistent supersoft X-ray source in M31
• A Transient Black-Hole Low-Mass X-Ray Binary Candidate in Centaurus A
• Globular Clusters and X-ray Point Sources in Centaurus A (NGC 5128)
• Three X-ray transients in M31 observed with Swift