Is there a non-stationary γ-ray emission zone 42 pc from the 3C 279 core?

Abstract

We investigate the relationship between the variable gamma-ray emission and jet properties in the blazar 3C 279 by combining the Fermi-LAT data spanning a period of eight years and concurrent radio measurements made at multiple epochs with VLBA at 15 and 43 GHz within the MOJAVE and VLBA-BU monitoring programmes. The aim of this paper is to compare the flux variability of the different components found in the VLBA observations, to the variability in the gamma-rays. This analysis helps us to investigate whether any of the jet components can be associated with the gamma-ray variability. Through Spearman rank correlation we found that the gamma-ray variability is correlated with a particular region (feature B in the MOJAVE images) downstream from the observed base (core) of the jet. This jet component is therefore a likely location where an important fraction of the variable gamma-ray emission is produced. We also calculated the average proper motion of the component with respect to the VLBA core and found that it moves at an apparent superluminal velocity of (3.70 ± 0.35)c, implying that one of the gamma-ray emission zones is not stationary. This jet component is also found between 6.86 mas and 8.68 mas, which translates to a distance from the radio core of at least 42 pc.