On a precessing jet-nozzle scenario with a common helical trajectory-pattern for blazar 3C345

Abstract

The kinematics and flux evolution of the superluminal knots in blazar 3C345 were interpreted in the framework of the precessing jet-nozzle scenario with a precessing common helical trajectory-pattern. We show that the jet in 3C345 precesses with a period of 7.3yr and the superluminal knots move consistently along a precessing common helical trajectory-pattern in their inner jet regions, which can extend to core distances of about 1.2mas or traveled distances of about 300pc (for knots C4 and C9). Through model-fitting of the observed kinematic behavior of the superluminal knots, their bulk Lorentz factor and Doppler factor were derived as continuous functions of time, which were used to investigate their flux evolution. We found that the light curves measured at 15, 22 and 43GHz can be well model-fitted in terms of their Doppler boosting profiles associated with their superluminal motion. Flux fluctuations on shorter time scales also exist due to knots' intrinsic variations in flux density and spectral index. The close association of the flux evolution with the Doppler boosting effect is important, firmly vadidating the precessing jet-nozzle scenario being fully appropriate to explain both the kinematics and emission properties of the superluminal knots in 3C345. We have proposed both the precessing jet-nozzle scenarios with a single jet and double jets (this paper and Qian[2022b]) to understand the VLBI phenomena in 3C345. VLBI-observations with higher resolutions deep into the core regions (core distances less than 0.1mas) are required to test them.