LMC X-1: Hybrid Black Hole Accretion?

Accretion in black hole binaries typically proceeds either via Roche lobe overflow or via a stellar wind. The former has high specific angular momentum, and forms a large, tidally truncated accretion disk, as seen in LMC X-3. The latter, exemplified by Cygnus X-1, has low specific angular momemtum, which likely creates a much smaller accretion disk. In this work, we focus on a system that appears to straddle the boundary between these two classes of accretion. LMC X-1, which has been regularly monitored by RXTE over the past two years, shows persistant disk blackbody emission. However, the disk luminosity shows an anomalous temperature dependence. Taken with the typical timescale of disk luminosity variations, this provides evidence that LMC X-1 has an unstable disk geometry caused by blobby accretion from its companion's stellar wind.