X-ray States of Black Hole Binaries in Outburst

We continue to probe the properties of stellar-size black holes and the physics of black-hole accretion using bright X-ray transients. Progress has been made in the recognizing that the three states of active accretion are related to different physical elements that may contribute radiation: the accretion disk, a jet, and a compact corona. Each of these states offers potential applications for investigation via general relativity in the regime of strong gravity. High-frequency QPOs are especially interesting in this regard, as the evidence mounts for their interpretation as stationary `voice-prints'that may constrain black-hole mass and spin.