The Galactic Black Holes Cyg X-1, GX 339−4, and 4U 1957+11: In Transition and at High Resolution

I review here some of the open questions regarding the geometry and emission mechanisms of galactic black hole candidates. For hard states, I concentrate on the perspective of “disk+Compton coronae” models (for discussions of jet models, see the papers by Sera Markoff). Specifically, I discuss the implications from our 10 year long RXTE monitoring campaign of Cyg X-1. I then present simultaneous RXTE /Chandra observations of the “soft state” black hole candidate 4U 1957+11, and discuss to what extent it does or does not allow one to test “relativistic disk models”. The use of such models has been claimed to measure black hole spin parameters. I then briefly present a particularly freaky-weird observation of GX339−4, where the source “fell off” the usual radio/X-ray correlation in the low/hard state. Questions addressed by the above observations include: are the Compton corona models unique fits to the data? (No. Jets work equally well, and simple broken power laws work better still. We argue that the latter models indicate multiple, broad-band continuum components.) Is there good evidence for a receding disk as sources transit into the hard state? (The jury is still out.) What does the relativistically broadened Fe line tell us? (Sometimes the disk, even into quiescence, stays very close to the central object, in contrast to expectations of ADAF models.) How much better/more necessary are recently discussed relativistic disk models? (I am very doubtful that such models will ever usefully measure black hole spin.)