Gleaning Secrets from the Transverse Profiles of AGN jets

Abstract

Both the emission properties and evolution of Active Galactic Nuclei (AGN) radio jets are dependent on the magnetic fields that thread them. A better understanding of these magnetic fields is therefore important in helping our understanding of jets in AGN. Several observations of jets have suggested that, on parsec scales, the jet magnetic field may have a significant helical component. Using a model first proposed by Laing and developed by Papageorgiou and Cawthorne, all of the above observations can be reproduced by varying only the helical pitch angle of the magnetic field and the line of sight angle. In order to reduce the total polarization to agree with observed values, a tangled magnetic field component is also introduced to the model, via another parameter, the degree of entanglement. We are in the process of comparing data from observations of several AGN with this model, making it possible to derive estimates of the helical pitch angle, the
viewing angle and the degree of entanglement for these jets in the framework of this model. The observed profiles are compared with a set of theoretical profiles. This proves to be an objective approach to profile fitting that should enable analysis of a large number of AGN jets, making it
possible to look for trends. Results for Mrk501 are presented.