Luminosity function of faint Galactic sources in the Chandra bulge field

Abstract

We study the statistical properties of faint X-ray sources detected in the Chandra bulge field. The unprecedented sensitivity of the Chandra observations allows us to probe the population of faint Galactic X-ray sources down to luminosities L2-10 keV∼ 1030 erg s−1 at the Galactic Centre distance. We show that the luminosity function of these CBF sources agrees well with the luminosity function of sources in the solar vicinity. The cumulative luminosity density of sources detected in the CBF in the luminosity range 1030–1032 erg s−1 per unit stellar mass is L2-10 keV/M★= (1.7 ± 0.3) × 1027 erg s−1 M−1⊙. Taking into account sources in the luminosity range 1032–1034 erg s−1 from Sazonov et al. 2006, the cumulative luminosity density in the broad luminosity range 1030–1034 erg s−1 becomes L2-10 keV/M★= (2.4 ± 0.4) × 1027 erg s−1 M−1⊙. The majority of sources with the faintest luminosities should be active binary stars with hot coronae based on the available luminosity function of X-ray sources in the solar environment.