Study of spectral and polarimetric properties of soft X-rays from stellar-mass black hole accretion disks

To understand the physics of black holes, the study of their spectral and X-ray polarimetric properties is becoming more and more important, thanks mainly to the development of new techniques that allow us to improve our measurements. Photons emitted from the BH accretion disc interact with the matter (basically electrons) of the accretion disc atmosphere, making the emerging radiation polarized. For symmetry reasons, the photon electric field is expected to oscillate either perpendicular or parallel to the disc's symmetry axis; however, due to general relativistic effects, the polarization plane should rotate with respect to its original orientation, an effect known as gravitational Faraday rotation. We will also consider the contribution of returning radiation, i.e. photons forced by strong gravity to return to the accretion disc, and the absorption effects that deeply modify the polarization properties with respect to the pure scattering limit. This literature review will highlight how considering all these effects together is crucial for correctly interpreting X-ray observations and accurately measuring fundamental black hole parameters, such as their spin