Polarization of Synchrotron Radiation from Relativistic Schwarzschild Circular Geodesics

The pattern of geodesic synchrotron radiation emitted by a charge in an orbit close to the circular photon orbit at $3M$ around a nonrotating black hole of mass $M$ is studied. The analysis is carried out using Stokes parameters, which completely characterize the state of the wave. The linear polarization, as observed at infinity, is total in the orbital plane and not smaller than 90% at the half-width of the beam. At the poles, pure circular polarization would be observed. In the region between the orbit plane and the poles the polarization shows features not present in ordinary synchrotron radiation. In our model, parameters more sensitive to deviations from the orbital plane are the Stokes parameter $s_2$ and the tilt angle of the polarization ellipse.