Young rotation-powered pulsars as ultra-luminous X-ray sources
  The aim of the present paper is to investigate a possible contribution of the
rotation-powered pulsars and pulsar wind nebulae to the population of
ultraluminous X-ray sources (ULXs). We first develop an analytical model for
the evolution of the distribution function of pulsars over the spin period and
find both the steady-state and the time-dependent solutions. Using the recent
results on the X-ray efficiency dependence on pulsar characteristic age, we
then compute the X-ray luminosity function (XLF) of rotation-powered pulsars.
In a general case it has a broken power-law shape with a high luminosity
cutoff, which depends on the distributions of the birth spin period and the
magnetic field.
  Using the observed XLF of sources in the nearby galaxies and the condition
that the pulsar XLF does not exceed that, we find the allowed region for the
parameters describing the birth period distribution. We find that the mean
pulsar period should be greater than 10-40 ms. These results are consistent
with the constraints obtained from the X-ray luminosity of core-collapse
supernovae. We estimate that the contribution of the rotation-powered pulsars
to the ULX population is at a level exceeding 3 per cent. For a wide birth
period distribution, this fraction grows with luminosity and above 10E40 erg/s
pulsars can dominate the ULX population.
