Polarized emission of orbiting hot spots near Sagittarius A*. Effects of electromagnetic interaction

We investigated the polarimetric signatures of orbiting hot spots around a Schwarzschild black hole in the presence of an external magnetic field, accounting for the electromagnetic interaction between the charged emitter and the field. Using a general-relativistic model that incorporates synchrotron emission and ray-tracing of light propagation, we analyzed how the electromagnetic interaction parameter modifies the observed polarization patterns, with particular emphasis on the behavior of the electric vector position angle and the time-evolving polarization loops in the Q-U plane. Applying the model to millimeter-wavelength ALMA observations of Sagittarius A*, we explored the parameter space that best reproduces the asymmetry, time ratio, and area ratio of the observed polarization loops. We find that the inclusion of a small positive interaction parameter increases the symmetry of the loops and the time ratio, while a negative magnetic parameter introduces strong asymmetry and fails to reproduce the data. Our results indicate that electromagnetic interaction can lead to ambiguity in the estimation of the system parameters such as orbital inclination or hot-spot velocity.