PoGO+ polarimetric constraint on the synchrotron jet emission of Cygnus X-1

Understand

We report a polarimetric constraint on the hard X-ray synchrotron jet emission from the Cygnus X-1 black-hole binary system.

• The observational data were obtained using the PoGO+ hard X-ray polarimeter in July 2016, when Cygnus X-1 was in the hard state.
• We have previously reported that emission from an extended corona with a low polarization fraction is dominating, and that the polarization angle is perpendicular to the disk surface.
• In the soft gamma-ray regime, a highly-polarized synchrotron jet is reported with INTEGRAL observations.