Parsec-scale jet precession and a putative supermassive binary black hole system in the blazar AO 0235+164

ABSTRACT The blazar AO 0235+164 is a key source for studying the interplay between multiwavelength variability in its light curves and changes in the position angles and apparent velocities of its parsec-scale jet components. In this work, we analyse public interferometric radio maps of AO 0235+164 at 15 and 43 GHz, using the Cross Entropy global optimization technique to determine the structural parameters of its jet components. We identified 36 kinematically distinct jet components across all sky quadrants, indicating a highly relativistic parsec-scale jet with a minimum Lorentz factor of $34\pm 7$ and a maximum viewing angle of $37\pm 8^{\circ }$. The temporal evolution of these jet components was modelled as a relativistic jet under a constant precession rate. The optimal clockwise precession model has a precession period of $8.4\pm 0.2$ yr, consistent with the 8.13-yr periodicity previously detected in optical light curves, besides providing a time-variable Doppler boosting factor correlated with the most intense flares at gamma-ray energies. For the counter-clockwise precession, a period of $6.0\pm 0.1$ yr is found, compatible with the 5–6-yr periodicities detected at radio and optical wavelengths. It is plausible that a supermassive black hole binary system in the nucleus of AO 0235+164 drives the parsec-scale jet precession and induces nodding motions consistent with short-term continuum periodicities. None the less, alternative scenarios (e.g. intrinsic curved jet, warped accretion disc instabilities, Lense–Thirring/Bardeen–Petterson effects, dual jets) cannot be ruled out as causes or optional explanations for the precession.