1920011

One of the most important results on Galactic black holes that has come out of INTEGRAL was the discovery of the signature of strong polarization of the >300 keV spectrum of Cygnus X-1. This discovery is an indication that this spectral component is due to synchrotron emission probably from the radio jet that is present in the hard state. In this two year 2 Ms program we propose a continuation of these measurements with the aim of detecting changes in the hard state polarization properties to set strong limits on the hard tail in the soft state and to break degeneracies between the two families of models for the formation of the hard tail. [truncated! Please see actual data for full text]