Synchrotron polarization signatures of surface waves in supermassive black hole jets

TL;DR

This paper uses GRMHD simulations to identify polarization signatures of surface waves at the jet-wind interface in supermassive black hole jets, which could be observed by future VLBI telescopes.

Contribution

It introduces the first simulation-based prediction of polarization signatures caused by surface waves in black hole jets, linking wave dynamics to observable polarization features.

Findings

Waves are launched from the black hole vicinity and propagate along the jet-wind interface.

Surface waves generate distinctive polarization signatures detectable in total intensity and linear polarization.

Polarization signatures could be observed by next-generation VLBI instruments like the Event Horizon Telescope.

Abstract

Supermassive black holes in active galactic nuclei (AGN) are known to launch relativistic jets, which are observed across the entire electromagnetic spectrum and are thought to be efficient particle accelerators. Their primary radiation mechanism for radio emission is polarized synchrotron emission produced by a population of non-thermal electrons. In this Letter, we present a global general relativistic magnetohydrodynamical (GRMHD) simulation of a magnetically arrested disk (MAD). After the simulation reaches the MAD state, we show that waves are continuously launched from the vicinity of the black hole and propagate along the interface between the jet and the wind. At this interface, a steep gradient in velocity is present between the mildly relativistic wind and the highly relativistic jet. The interface is, therefore, a shear layer, and due to the shear, the waves generate roll-ups that alter the magnetic field configuration and the shear layer geometry. We then perform polarized radiation transfer calculations of our GRMHD simulation and find signatures of the waves in both total intensity and linear polarization, effectively lowering the fully resolved polarization fraction. The tell-tale polarization signatures of the waves could be observable by future Very Long Baseline Interferometric observations, e.g., by the next-generation Event Horizon Telescope.