2011MNRAS.415.2081C

We investigate the emission properties that a large-scale helical magnetic field imprints on active galactic nuclei (AGN) jet synchrotron radiation. A cylindrically symmetric relativistic jet and large-scale helical magnetic field produce significant asymmetrical features in transverse profiles of fractional linear polarization, intensity, the Faraday rotation and spectral index. The asymmetrical features of these transverse profiles correlate with one another in ways specified by the handedness of the helical field, the jet viewing angle (θ_ob) and the bulk Lorentz factor of the flow (Γ). Thus, these correlations may be used to determine the structure of the magnetic field in the jet. In the case of radio galaxies (θ_ob ∼ 1 rad) and a subclass of blazars with particularly small viewing angles (θ_ob≪ 1/Γ), we find an edge-brightened intensity profile that is similar to that observed in the radio galaxy M87. We present observations of the AGNs 3C 78 and NRAO 140 that display the type of transverse asymmetries that may be produced by large-scale helical magnetic fields.