Polarization signatures of strong gravity in black-hole accretion discs

Abstract

We discuss the effects of strong gravity on the polarization properties of a black hole accretion disc. The intrinsic polarization is computed taking into account light scattered on the disc surface and using different approximations. The gravitational field of a black hole influences the Stokes parameters of reflected radiation propagating to a distant observer. The lamp-post model is explored as an example of a specific geometrical arrangement relevant for AGNs. The degree and the angle of polarization are computed as functions of the observer inclination angle, of the inner radius of the disc emitting region, and of other parameters of the model. The expected polarization should be detectable by new generation polarimeters. This contribution extends results reported in our recent paper (MNRAS 355, 1005; 2004).