Polarization Observations of AGN Jets: Past and Future

TL;DR

This paper reviews polarization observations of AGN jets across multiple wavelengths, discusses the challenges in interpreting magnetic field structures, and highlights recent VLBI findings and future prospects for studying magnetic fields near supermassive black holes.

Contribution

It provides a comprehensive review of polarization effects in AGN jets, summarizes recent VLBI polarization observations, and discusses new calibration and imaging techniques for magnetic field analysis.

Findings

Detection of significant polarization and Faraday rotation in some nearby AGN jets.

Recent VLBI observations reveal magnetic field structures in jet launching regions.

Advancements in polarization calibration improve analysis of magnetic fields around black holes.

Abstract

The magnetic field is believed to play a critical role in the bulk acceleration and propagation of jets produced in active galactic nuclei (AGN). Polarization observations of AGN jets provide valuable information about their magnetic fields. As a result of radiative transfer, jet structure, and stratification, among other factors, it is not always straightforward to determine the magnetic field structures from observed polarization. We review these effects and their impact on polarization emission at a variety of wavelengths, including radio, optical, and ultraviolet wavelengths in this paper. It is also possible to study the magnetic field in the launching and acceleration regions of AGN jets by using very long baseline interferometry (VLBI), which occurs on a small physical scale. Due to the weak polarization of the jets in these regions, probing the magnetic field is generally difficult. However, recent VLBI observations have detected significant polarization and Faraday rotation in some nearby sources. We present the results of these observations as well as prospects for future observations. Additionally, we briefly discuss recently developed polarization calibration and imaging techniques for VLBI data, which enable more in-depth analysis of the magnetic field structure around supermassive black holes and in AGN jets.