PKS 0735+178 optical and radio light curves

A characteristic variability time-scale of ~10-11yr is robustly detected in the radio-mm bands (>=3{sigma}), while the optical and gamma-ray data show weaker, shorter period signals. The independent constraints from the VLBI core-shift measurements and radio time delays yield consistent estimates of the jet geometry and disturbance propagation, supporting variability governed by jet propagation effects. The long-term modulation is consistent with a slow variation in energy release at the jet base, while individual flares arise from shocks propagating downstream.

Jet precession may contribute to the long-term modulation; however, the required viewing angles are inconsistent with the VLBI constraints, indicating that precession alone cannot explain the observed variability.