Low-luminosity X-ray sources and the Galactic ridge X-ray emission

Abstract

Using the XMM-Newton Slew Survey, we construct a hard-band selected sample of low-luminosity Galactic X-ray sources. Two source populations are represented, namely coronally-active stars and binaries (ASBs) and cataclysmic variables (CVs), with X-ray luminosities collectively spanning the range 10^(28-34) erg/s (2-10 keV). We derive the 2-10 keV X-ray luminosity function (XLF) and volume emissivity of each population. Scaled to the local stellar mass density, the latter is found to be 1.08 +/- 0.16 x 10^28 erg/s/M and 2.5 +/- 0.6 x 10^27 erg/s/M, for the ASBs and CVs respectively, which in total is a factor 2 higher than previous estimates. We employ the new XLFs to predict the X-ray source counts on the Galactic plane at l = 28.5 deg and show that the result is consistent with current observational constraints. The X-ray emission of faint, unresolved ASBs and CVs can account for a substantial fraction of the Galactic ridge X-ray emission (GRXE). We discuss a model in which roughly 80 per cent of the 6-10 keV GRXE intensity is produced in this way, with the remainder attributable to X-ray scattering in the interstellar medium and/or young Galactic source populations. Much of the hard X-ray emission attributed to the ASBs is likely to be produced during flaring episodes.

References in corpus (16)

• The first XMM-Newton slew survey catalogue: XMMSL1
• X-Ray Spectroscopy of Stars
• Discrete sources as the origin of the Galactic X-ray ridge emission
• Gamma-ray continuum emission from the inner Galactic region as observed with INTEGRAL/SPI
• Hard X-ray emission from the Galactic ridge
• Nonthermal Hard X-ray Emission and Iron Kalpha Emission from a Superflare on II Pegasi
• Scaling laws of solar and stellar flares
• A Chandra Catalog of X-ray Sources in the Central 150 pc of the Galaxy
• A study of X-ray flares - I. Active late-type dwarfs
• Properties of the Galactic population of cataclysmic variables in hard X-rays
• Spatial distribution and galactic model parameters of cataclysmic variables
• On the contribution of point sources to the Galactic ridge X-ray emission
• Geometry Diagnostics of a Stellar Flare from Fluorescent X-rays
• Hard X-rays and Fluorescent Iron Emission from the Embedded Infrared Cluster in NGC 2071
• Chasing the Identification of ASCA Galactic Objects (ChIcAGO) - An X-ray Survey of Unidentified Sources in the Galactic Plane I: Source Sample and Initial Results
• The Unusual Cataclysmic Binary Star RBS 0490 and the Space Density of Cataclysmics

Cited by in corpus (7)

• Magnetic White Dwarfs
• The Central 300 pc of the Galaxy probed by infrared spectra of H${}_3^{+}$ and CO: part I. Predominance of warm and diffuse gas and high H${}_2$ ionization rate
• Diffuse X-Ray Sky in the Galactic Center
• Origin of the Galactic Diffuse X-ray Emission: Iron K-shell Line Diagnostics
• The X-ray Emissivity of Low-Density Stellar Populations
• Broad Observational Perspectives Achieved by the Accreting White Dwarf Sciences in the XMM-Newton and Chandra Eras
• Determining the Nature of Faint X-Ray Sources from the ASCA Galactic Center Survey