Correlations between the peak flux density and the position angle of inner-jet in three blazars

TL;DR

This study investigates the relationship between flux density and jet position angle in blazars, revealing diverse correlations and suggesting geometric beaming effects as a key factor, with some sources showing quasi-periodic behavior.

Contribution

It provides the first detailed analysis of long-term flux and position angle correlations in blazars, including modeling of non-ballistic and precession jet scenarios.

Findings

Approximately 20% of sources show significant flux-PA correlations.

Different correlation signs are observed, positive in some and negative in others.

Some correlations can be explained by geometric jet precession models.

Abstract

We aim to investigate the relation between the long-term flux density and the position angle (PA) evolution of inner-jet in blazars. We have carried out the elliptic Gaussian model-fit to the `core' of 50 blazars from 15 GHz VLBA data, and analyzed the variability properties of three blazars from the model-fit results. Diverse correlations between the long-term peak flux density and the PA evolution of the major axis of the `core' have been found in $\sim$ 20% of the 50 sources. Of them, three typical blazars have been analyzed, which also show quasi-periodic flux variations of a few years (T). The correlation between the peak flux density and the PA of inner-jet is positive for S5~0716+714, and negative for S4~1807+698. The two sources cannot be explained with the ballistic jet models, the non-ballistic models have been analyzed to explain the two sub-luminal blazars. A correlation between the peak flux density and the PA (with a T/4 time lag) of inner-jet is found in [HB89]~1823+568, this correlation can be explained with a ballistic precession jet model. All the explanations are based mainly on the geometric beaming effect; physical flux density variations from the jet base would be considered for more complicated situations in future, which could account for the no or less significance of the correlation between the peak flux density and the PA of inner-jet in the majority blazars of our sample.