Bright end of the luminosity function of high-mass X-ray binaries: contributions of hard, soft and supersoft sources
Abstract
Using a spectral analysis of bright Chandra X-ray sources located in 27 nearby galaxies and maps of star-formation rate (SFR) and interstellar medium surface densities for these galaxies, we constructed the intrinsic X-ray luminosity function (XLF) of luminous high-mass X-ray binaries (HMXBs), taking into account absorption effects and the diversity of HMXB spectra. The XLF per unit SFR can be described by a power-law dN/dlog LX,unabs ≈ 2.0(LX,unabs/1039 erg s-1)-0.6 (M⊙ yr-1)-1 from LX,unabs = 1038 to 1040.5 erg s-1, where LX,unabs is the unabsorbed luminosity at 0.25-8 keV. The intrinsic number of luminous HMXBs per unit SFR is a factor of ∼2.3 larger than the observed number reported before. The intrinsic XLF is composed of hard, soft and supersoft sources (defined here as those with the 0.25-2 keV to 0.25-8 keV flux ratio of <0.6, 0.6-0.95 and >0.95, respectively) in ∼ 2:1:1 proportion. We also constructed the intrinsic HMXB XLF in the soft X-ray band (0.25-2 keV). Here, the numbers of hard, soft and supersoft sources prove to be nearly equal. The cumulative present-day 0.25-2 keV emissivity of HMXBs with luminosities between 1038 and 1040.5 erg s-1 is ∼5 × 1039 erg s-1(M⊙ yr-1)-1, which may be relevant for studying the X-ray preheating of the early Universe.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2017
- DOI:
- 10.1093/mnras/stw3113
- arXiv:
- arXiv:1612.01261
- Bibcode:
- 2017MNRAS.466.1019S
- Keywords:
-
- stars: massive;
- galaxies: star formation;
- early Universe;
- X-rays: binaries;
- X-rays: galaxies;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 37 pages, 40 figures, accepted for publication in MNRAS