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A. Zezas, G. Fabbiano (CfA), M. Ward (University of Leicester), A. Prestwich, S. Murray (CfA)
We present a detailed study of the discrete sources detected in the {\em Chandra} observations of the prototypical star-forming galaxies M82 and Antennae. In both objects we detect a large number of sources with diverse properties. The majority of them, based on their variability and spectra, are identified as X-ray binaries. A very important result is the confirmation of previous indications that there is a population of sources with X-ray luminosities much higher than the the Eddington limit for a 1M\odot neutron star, suggesting that they are associated with BH binaries with compact objects in the 10-1000M\odot mass range. Here we present evidence that indeed these sources are most probably X-ray binaries and we study their temporal and spectral properties as an attempt to connect this new population with the well known galactic X-ray binaries. We also discuss other alternative models for their origin (beamed sources, compact supernovae, compact clusters) and we show that their statistics, generaly hard spectra (\Gamma=0.8-1.3) and variability do not favor these models.