Sources of “ the Antennae ”

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. Subject headings: galaxies: peculiar — galaxies: individual(NGC4038/39) — galaxies: interactions — X-rays: galaxies — X-ray: binaries