A population synthesis study on the faint X-ray sources in the Galactic center region

Abstract

Context.Recent Chandra observations of the Galactic center region (GCR) have uncovered a population of faint discrete X-ray sources. A few theoretical works have already investigated the nature of these sources.Aims.We examine the contributions and luminosity functions of various kinds of candidate objects that have been proposed either by previous authors or by ourselves.Methods.We conduct a population synthesis calculation based on the Hurley et al. rapid binary evolution code. Several candidate models, i.e. wind-accreting neutron stars, intermediate polars, low mass X-ray binaries, young pulsars, and massive stars with strong winds, are incorporated into our calculation. We also take the geometric effect of the accretion disk into account for Roche lobe overflow X-ray binaries.Results.Our results show that neutron star low-mass X-ray binaries contribute significantly to the observed sources. We also point out that wind-accreting neutron stars contribute negligible amount to these sources due to the propeller effect, and the intermediate polars play a minor role in accounting for the faint X-ray sources in both the Wang et al. and Muno et al. survey. It should be mentioned that the majority of the sources in the survey field of Wang et al. are still beyond what we can expect to find.