Bright end of the luminosity function of high-mass X-ray binaries: contributions of hard, soft and supersoft sources

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 highmass 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) approximate to 2.0(LX, (unabs)/10(39) erg s(-1))(-0.6) (M-circle dot yr(-1))(-1) from LX, (unabs) = 10(38) to 10(40.5) 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 similar to 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 similar to 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 presentday 0.25-2 keV emissivity of HMXBs with luminosities between 10(38) and 10(40.5) erg s(-1) is similar to 5 x 10(39) erg s(-1)(M-circle dot yr(-1))(-1), which may be relevant for studying the X-ray preheating of the early Universe.