Rotation Measures in AGN jets seen by VLA at 21 cm to 6 mm

TL;DR

This study measures Faraday Rotation Measures across a broad frequency range in seven AGNs, revealing frequency-dependent RM behavior and temporal variations, providing insights into magnetic field structures in AGN jets.

Contribution

First to calculate RMs over a wide wavelength range from 21 cm to 6 mm in multiple AGNs, showing frequency dependence and temporal RM variations.

Findings

RM increases with frequency following |RM|~f^a with a=1.6±0.1

Observed extremely high RM in 0710+439, one of the highest recorded

RM varies over time, indicating changing physical conditions in AGN jets

Abstract

We present Faraday Rotation Measure (RM) properties of seven active galactic nuclei (AGN), observed with the NRAO VLA at three epochs in 2012-2014. Data was taken at 1.4, 2.2, 5.0, 8.2, 15.4, 22.4, 33.5 and 43.1 GHz quasi simultaneously in full polarization mode. For the first time RMs were calculated in a range of wavelengths covering more than one order of magnitude: from 21 cm up to 6 mm. We measured RM for each source and showed a tendency to increase its value toward high frequencies according to the law |RM|~f^a with a=1.6+/-0.1. For 0710+439, we observed an increase over the frequency range of 4 orders of magnitude and measured one of the highest RM ever, (-89+/-1)*10^3 rad/m^2. Analysis of different epochs shows variations of the value and the sign of RM on short and long time-scales. This may be caused by changing physical conditions in the compact regions of the AGN jets, e.g. strength of magnetic field, particle density and so on.