Watching the formation and evolution of compact jets from accreting black holes

Accreting black holes (BHs) produce a steady compact jet when they are in hard states with a high level of timing noise and a hard X-ray spectrum. As this is the only time that steady jets are seen from Galactic BHs, studies of this state provide an opportunity to improve our understanding of the disk conditions necessary to launch jets. We are taking advantage of this opportunity by carrying out a multi-wavelength program to observe BH transients as they are entering the hard state and the compact jet is turning on. One of our recent projects is a study of radio-to-X-ray spectral energy distributions (SEDs) from the microquasar GRO J1655-40. Novel aspects of the study include obtaining mid-IR coverage with the Spitzer Space Telescope, which we used to constrain the level of synchrotron emission from the jet. Also, we fitted the hard state SEDs with a physical compact jet model. Here, we describe our results for GRO J1655-40 as well as results from our broader observational BH program.