Unraveling circular polarimetric images of magnetically arrested accretion flows near event horizon of a black hole

Magnetically arrested accretion flows are thought to fuel some of the supermassive black holes and to power their relativistic jets. We calculate and study a time sequence of linear and circular polarimetric images of numerical, high resolution, and long-duration simulations of magnetically dominated flows to investigate observational signatures of strong magnetic fields near the event horizon of a non-rotating black hole. We find that the magnitude of resolved linear and circular polarizations is rather sensitive to the assumption of the coupling of electron and ions in the accretion flow. Models with cooler electrons have higher Faraday rotation and conversion depths, which result in scrambled linear polarization and enhanced circular polarization. In those high Faraday thickness cases, the circular polarization is particularly sensitive to dynamics of toroidasl-radial magnetic fields in the accretion flows. The models with high Faraday thickness are characterized by nearly constant handedness of circular polarization, consistent with observations of some accreting black holes. We also find that the emission region produced by light, which is lensed around the black hole, shows inversion of circular polarization handedness with respect to the handedness of the circular polarization of the entire emission region. Such polarity inversions are unique to near horizon emission.

Automated summary

By studying high resolution simulations, it is found that the coupling of electron and ions in magnetically arrested accretion flows significantly affects the linear and circular polarizations. In cases with high Faraday thickness, circular polarization is particularly sensitive to the dynamics of toroidal-radial magnetic fields.