X-ray luminosity function of faint point sources in the Milky Way
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85740 Garching bei München, Germany e-mail: firstname.lastname@example.org
2 Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow, Russia
Accepted: 15 December 2005
We assessed the contribution to the X-ray (above 2 keV) 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 to construct an X-ray luminosity function (XLF) of nearby X-ray sources in the range (where Lx is the luminosity over 2–10 keV), occupied by coronally active binaries (ABs) and cataclysmic variables (CVs). We then extended this XLF down to using the Rosat All-Sky Survey in soft X-rays and available information on the 0.1–10 keV spectra of typical sources. We found that the local cumulative X-ray (2–10 keV) emissivities (per unit stellar mass) of ABs and CVs are 1027 and 1027 erg s-1 , respectively. In addition to ABs and CVs representing old stellar populations, young stars locally emit 1027 erg s. Finally to the XLF of ABs and CVs we attached a high luminosity branch (up to ~1039 erg s-1) 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 2–10 keV luminosity of the Milky Way is ~2 1038 erg s-1, 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.
Key words: stars: luminosity function, mass function / Galaxy: structure / X-rays: binaries / X-rays: galaxies / X-rays: stars
© ESO, 2006