Microquasars in the low/hard state: strong coronae, compact jets, and the high frequency variability

Abstract

We apply a model of magnetically dominated coronae above standard accretion discs to the low/hard state of galactic black holes. When the disc-corona coupling is accounted for self-consistently assuming that magneto-rotational instability is at work in the disc, and that the corona is generated by buoyant escape of disc magnetic structures, then the model predicts powerful, X-ray emitting coronae at low accretion rates. A main consequence is discussed: the possibility that the corona itself is the launching site of powerful, MHD driven jets/outflows. This depends crucially of the coronal scaleheight. Finally, we present the first radial profiles of a corona a different accretion rates, and discuss their implications for high frequency variability.