A possible precession period for superluminal ejection in QSO 3C 279

The search for periodic features in flux variability and superluminal ejection in blazars has been an important subject, which is helpful for providing significant clues to the understanding of the structure and kinematics of relativistic jets (physical processes of acceleration and collimation) and their association with central energy engines (black hole/accretion disk systems). The wobbling of the ejection position angle of VLBI knots in superluminal sources has been interpreted in terms of the precession of the jet ejection nozzle as one of the alternative interpretations. We study the change with time of the initial position angle of superluminal knots in QSO 3C 279, using VLBI-data collected from the literature spanning more than ∼30 yr and propose a jet-nozzle precession model which has very small viewing angles (less than 20) to fit the long-term trends in both variations in the inner-jet position angle (Chatterjee et al.) and the ejection position angle of the VLBI components. It is shown that an ejection-nozzle precession period of ∼25 yr could be appropriate to fit the long-term trend in the variation of the ejection position angle. However, the short-term swings and fluctuations in the ejection position angle cause some uncertainties. We also fit a model to the trajectory of component C4, correcting its non-ballistic motion near the core. (research papers)