Helical magnetic field structure in 3C 273. A Faraday rotation analysis using multi-frequency polarimetric VLBA data

TL;DR

This study uses multi-frequency VLBA polarimetric data to analyze the rotation measure of quasar 3C 273, revealing a helical magnetic field structure and its temporal evolution, which sheds light on jet collimation and environmental dynamics.

Contribution

It provides the first detailed RM gradient map of 3C 273's jet at multiple frequencies, demonstrating a helical magnetic field and its temporal changes.

Findings

Detected a transverse RM gradient indicating a helical magnetic field.

Observed temporal variations in RM suggest a dynamic jet environment.

Revealed interactions between the jet and surrounding medium influence magnetic field structure.

Abstract

We present a study on rotation measure (RM) of the quasar 3C 273. This analysis aims to discern the magnetic field structure and its temporal evolution. The quasar 3C 273 is one of the most studied active galactic nuclei due to its high brightness, strong polarization, and proximity, which enables resolving the transverse structure of its jet in detail. We used polarized data from 2014, collected at six frequencies (5, 8, 15, 22, 43, 86 GHz) with the Very Long Baseline Array, to produce total and linear polarization intensity images, as well as RM maps. Our analysis reveals a well-defined transverse RM gradient across the jet, indicating a helical, ordered magnetic field that threads the jet and likely contributes to its collimation. Furthermore, we identified temporal variations in the RM magnitude when compared with prior observations. These temporal variations show that the environment around the jet is dynamic, with changes in the density and magnetic field strength of the sheath that are possibly caused by interactions with the surrounding medium.