A Long, Hard Look at the Low/Hard State in Accreting Black Holes

We present the first results of coordinated multi-wavelength observations ofthe Galactic black hole GX 339-4 in a canonical low-hard state, obtained duringits 2004 outburst. XMM-Newton observed the source for 2 revolutions, orapproximately 280 ksec; RXTE monitored the source throughout this long stare.The resulting data offer the best view yet obtained of the inner accretion flowgeometry in the low-hard state, which is thought to be analogous to thegeometry in low-luminosity active galactic nuclei. The XMM-Newton spectraclearly reveal the presence of a cool accretion disk component, and arelativistic Fe K emission line. The results of fits made to both componentsstrongly suggest that a standard thin disk remains at or near to the innermoststable circular orbit, at least in bright phases of the low-hard state. Thesefindings indicate that potential links between the inner disk radius and theonset of a steady compact jet, and the paradigm of a radially-recessed disk inthe low-hard state, do not hold universally. The results of our observationscan best be explained if a standard thin accretion disk fuels a corona which isclosely related to, or consistent with, the base of a compact jet. In a briefexamination of archival data, we show that Cygnus X-1 supports this picture ofthe low/hard state. We discuss our results within the context of disk-jetconnections and prevailing models for accretion onto black holes.Comment: 13 pages, 10 figures (6 in color), ApJ, in pres