Observing Extremes of Accretion
The X-ray band provides a view of extreme accretion regimes in neutron star and black hole binaries. I will discuss insights gained from broad band observations of X-ray binaries, with emphasis on ultraluminous X-ray sources (ULXs). ULXs, identified as bright off-nuclear X-ray sources in nearby galaxies, have apparent luminosities significantly in excess of the Eddington luminosity for a stellar-remanant black hole. This diverse population provides a window on regimes of super-Eddington accretion, and a few sources may harbor large black holes.