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

TL;DR

This study uses high-resolution simulations to analyze the polarimetric signatures of magnetically arrested accretion flows near black holes, revealing how magnetic field dynamics influence observable polarization features.

Contribution

It provides new insights into the polarization signatures of accretion flows near black holes, highlighting the impact of electron-ion coupling and magnetic field configurations on polarization observables.

Findings

Circular polarization is sensitive to magnetic field dynamics.

High Faraday thickness leads to stable polarization handedness.

Near horizon emission shows unique polarization inversions.

Abstract

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 results in scrambled linear polarization and enhanced circular polarization. In those high Faraday thickness cases the circular polarization is particularly sensitive to dynamics of toroidal-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.