X-ray luminosity function of faint point sources in the Milky WayS. Sazonov1, 2, M. Revnivtsev1, 2, M. Gilfanov1, 2, E. Churazov 1, 2 and R. Sunyaev1, 2
1 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85740 Garching bei München, Germany
2 Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow, Russia
(Received 3 October 2005 / 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 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