  We report the first results of the Chandra temporal monitoring of the
ultra-luminous X-ray sources (ULXs) in the Antennae galaxies (NGC 4038/39).
Observations at four different epochs, covering time scales of 2 years to 2
months, show variability in seven out of nine ULXs, confirming that they are
likely to be accreting compact X-ray binaries (XRBs). The seven variable ULXs
exhibit a variety of temporal and spectral behaviors: one has harder X-ray
colors with decreasing luminosity, similar to the black hole binary Cyg X-1,
but four other ULXs show the opposite behavior. We suggest that the latter may
be black-hole binaries accreting at very high rates.
