2008MNRAS.388.1457S

We study the jet and counterjet of the powerful classical double Fanaroff-Riley type II (FR II) radio galaxy CygnusA as seen in the 5-, 8- and 15-GHz radio bands using the highest spatial resolution and signal-to-noise ratio archival data available. We demonstrate that the trace of the radio knots that delineate the jet and counterjet deviates from a straight line and that the inner parts can be satisfactorily fitted with the precession model of Hjellming & Johnston. The parameter values of the precession model fits are all plausible although the jet speed is rather low (≲ 0.5c) but, on investigation, found to be consistent with a number of other independent estimates of the jet speed in CygnusA. We compare the masses and precession periods for sources with known precession and find that for the small number of active galactic nuclei with precessing jets the precession periods are significantly longer than those of microquasars.