Astronomy and Astrophysics, volume 450, 117-128 (2006/4-4)
X-ray luminosity function of faint point sources in the Milky Way.
SAZONOV S., REVNIVTSEV M., GILFANOV M., CHURAZOV E. and SUNYAEV R.
Abstract (from CDS):
We assessed the contribution to the X-ray (above 2keV) luminosity of the Milky Way by different classes of low-mass binary systems and single stars. We began by using the RXTE Slew Survey of the sky at |b|>10° to construct an X-ray luminosity function (XLF) of nearby X-ray sources in the range 1030erg/s<Lx<1034erg/s (where Lx is the luminosity over 2-10keV), occupied by coronally active binaries (ABs) and cataclysmic variables (CVs). We then extended this XLF down to Lx∼1027.5erg/s using the Rosat All-Sky Survey in soft X-rays and available information on the 0.1-10keV spectra of typical sources. We found that the local cumulative X-ray (2-10keV) emissivities (per unit stellar mass) of ABs and CVs are (2.0±0.8)x1027 and (1.1±0.3)x1027erg/s/M☉, respectively. In addition to ABs and CVs representing old stellar populations, young stars locally emit (1.5±0.4)x1027erg/s/M☉. Finally to the XLF of ABs and CVs we attached a high luminosity branch (up to ∼1039erg/s) composed of neutron-star and black-hole low-mass X-ray binaries (LMXBs), derived in previous work. The combined XLF covers ∼12 orders of magnitude in luminosity. The estimated combined contribution of ABs and CVs to the 2-10keV luminosity of the Milky Way is ∼2x1038erg/s, or ∼3% of the integral luminosity of LMXBs averaged over nearby galaxies. The XLF obtained in this work is used elsewhere to assess the contribution of point sources to the Galactic ridge X-ray emission.
stars: luminosity function, mass function - Galaxy: structure - X-rays: binaries - X-rays: galaxies - X-rays: stars