Polarization features of x-ray radiation emitted near black holes

We compare the X-ray polarization features of geometrically thick clouds surrounding a black hole and the standard accretion disk model. The calculations include a fully general-relativistic treatment of the radiation transfer problem. In both cases general-relativistic corrections can lead to large rotations in the plane of X-ray polarization and to changes in the degree of polarization. Such differences are potentially observable and can be used to distinguish between the two models. The polarization features can indicated whether a black hole is present in a compact X-ray source