2017MNRAS.466.1019S

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 L_X,unabs ≃ 2.0(L_X,unabs/10³⁹ erg s^–1)^–0.6 (M_☉ yr^–1)^–1 from L_X,unabs = 10³⁸ to 10^40.5 erg s^–1, where L_X,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 10^40.5 erg s^–1 is ∼5 x 10³⁹ erg s^–1(M_☉ yr^–1)^–1, which may be relevant for studying the X-ray preheating of the early Universe.