Monte Carlo Studies of Transverse Faraday Rotation Profiles

Faraday Rotation measurements are a very important tool for investigating the magnetic (B) fields associated with the relativistic jets of Active Galactic Nuclei (AGN); for example, a toroidal or helical B field component should give rise to a systematic gradient in the observed Faraday rotation across the jet. However, real observed radio images have finite resolution. Typical beam sizes for cm-wavelength Very Long Baseline Interferometry (VLBI) observations are often comparable to or larger than the observed jet widths, raising questions about how well resolved a jet must be in the transverse direction in order to reliably detect transverse Faraday-rotation structure. The results of new simulations of Faraday rotation images designed to directly investigate this question are presented, together with studies of the probabilities of observing spurious Faraday Rotation gradients as a result of random noise and finite resolution. These simulations clearly demonstrate the possibility of detecting transverse Faraday-rotation structures even when the observed intrinsic jet widths are considerably smaller than the beam width.