X-ray binaries (XRB) are known to exhibit different spectral states which are
associated with different black hole accretion modes. Recent measurments of
linear polarization of X-ray emission in X-ray binary Cygnus X-1 allow us to
test models for the hard state of accretion in a unique way. We show that
general relativistic radiative magnetohydrodynamic (GRRMHD) simulations of
accreting stellar black hole in a hard X-ray state are consisitent with the new
observational information. The state-of-the-art models of the hard state show
that the X-ray emission is predominantly produced by extended jets, away from
the central black hole with some contribution from hot corona near the black
hole. Our modeling results are supporting the idea that the strong correlations
between synchrotron and X-ray emission observed in many XRBs can be attributed
to the jet emission. In the presented framework, where first-principle models
have limited number of free parameters, the X-ray polarimetric observations put
constraints on the viewing angle of the accreting black hole system.Comment: 7 pages, 4 figures, invited contribution to a special issue of a
Springer Nature journal, comments are very welcom