  Using a sample of two hundred luminous (L_unabs>10^38 erg/s, where L_unabs is
the unabsorbed 0.25-8 keV luminosity) high-mass X-ray binary (HMXB) candidates
found with Chandra in 27 nearby galaxies, we have constructed the collective
X-ray spectrum of HMXBs in the local Universe per unit star formation rate,
corrected for observational biases associated with intrinsic diversity of HMXB
spectra and X-ray absorption in the interstellar medium. This spectrum is well
fit by a power law with a photon index Gamma=2.1+/-0.1 and is dominated by
ultraluminous X-ray sources with L_unabs>10^39 erg/s. Hard sources (those with
the 0.25-2 keV to 0.25-8 keV flux ratio of <0.6) dominate above ~2 keV, while
soft and supersoft sources (with the flux ratios of 0.6-0.95 and >0.95,
respectively) at lower energies. The derived spectrum probably represents the
angle-integrated X-ray emission of the near- and super-critically accreting
stellar mass black holes and neutron stars in the local Universe. It provides
an important constraint on supercritical accretion models and can be used as a
reference spectrum for calculations of the X-ray preheating of the Universe by
the first generations of X-ray binaries.
