Faraday rotation in the MOJAVE blazars: 3C 273 a case study

TL;DR

This study uses multi-frequency radio polarimetric observations to analyze Faraday rotation in the blazar 3C 273, providing evidence for a helical magnetic field and jet structure through observed rotation measure gradients.

Contribution

It presents the first observation of a zero-crossing in the rotation measure gradient in 3C 273, supporting the presence of a helical magnetic field in the jet.

Findings

Confirmed transverse rotation measure gradient in 3C 273

First detection of gradient crossing zero, indicating helical magnetic fields

Variability suggests different jet regions are illuminated at different epochs

Abstract

Radio polarimetric observations of Active Galactic Nuclei can reveal the magnetic field structure in the parsec-scale jets of these sources. We have observed the gamma-ray blazar 3C 273 as part of our multi-frequency survey with the Very Long Baseline Array to study Faraday rotation in a large sample of jets. Our observations re-confirm the transverse rotation measure gradient in 3C 273. For the first time the gradient is seen to cross zero which is further indication for a helical magnetic field and spine-sheath structure in the jet. We believe the difference to previous epochs is due to a different part of the jet being illuminated in our observations.