Spectral fit of ULX sources

The spectra of these sources were fitted using two spectral models (an absorbed power-law and a disk blackbody) to ascertain the dependence of estimated parameters on the spectral model used. It was found that the cumulative luminosity function depends on the choice of the spectral model, especially for luminosities >10^40^ergs/s.

A large number (~80) of the sources have luminosities >10^39^ergs/s (ultraluminous X-ray sources) with indistinguishable average spectral parameters (inner disk temperature ~1keV and/or photon index GAMMA~2) with those of the lower luminosity ones.