X-ray spectral and timing studies of black hole transients in the hard state at low luminosity

Our Suzaku program for observing accreting black holes has focused on studying transient systems in the hard state at low luminosity. This is the one state that is associated with the presence of a steady jet, and thus, understanding the physics of the hard state is critical to understanding the disk/jet connection. However, questions remain about the accretion geometry, its evolution, and its relation to jet production. With Suzaku, we have observed the black hole transients GX 339-4 and 4U 1630-47. Here, we compare the results from the two observations, focusing on the new 4U 1630-47 measurements. While the 4U 1630-47 observation occurred at a low luminosity (0.017%LEdd), and the spectrum is consistent with a hard state, the lack of variability is unusual. We discuss the implications of the lack of variability at such a low mass accretion rate.