Analytical ray-tracing of synchrotron emission around accreting black holes

Alexandra Veledina, Matthieu Pélissier

Published 2024-12-11Version 1

Polarimetric images of accreting black holes encode important information about laws of strong gravity and relativistic motions of matter. Recent advancements in instrumentation enabled such studies in two objects: supermassive black holes M87* and Sagittarius A*. Light coming from these sources is produced by synchrotron mechanism whose polarization is directly linked to magnetic field lines, and propagates towards the observer in a curved spacetime. We study the distortions of the gas image by the analytical ray-tracing technique for polarized light artpol, that is adapted for the case of synchrotron emission. We derive analytical expressions for fast conversion of intensity/flux, polarization degree and polarization angle from the local to observer's coordinates. We put emphasis on the non-zero matter elevation above the equatorial plane and non-circular matter motions. Applications of the developed formalism include static polarimetric imaging of the black hole vicinity and dynamic polarimetric signatures of matter close to the compact object.