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

Abstract

Aims. We aim to investigate the relation between the long-term flux density and the position angle (PA) evolution of inner-jet in blazars. Methods. 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. 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 ∼ 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. Conclusions.

Jet outflow and gamma-ray emission correlations in S5 0716+714

“…position angle or jet wobbling, have often been observed in blazars (Britzen et al 2009;Bach et al 2005;Rastorgueva et al 2011;Lister et al 2013;Molina et al 2014). In some cases the inner jet position angle (PA) variations were found to correlate with the flux density variations at radio frequencies (Britzen et al 2009;Liu et al 2012) and also with X-rays (Chatterjee et al 2008). However, a correlation between γ-ray flux and PA variations has not been reported so far.…”

Periods of the Long-Term Variability of the Blazar 0716+714 and Their Inter-Correlations in a Helical Jet Model

“…A helical shape suggests the presence of periodic variations of the angle between the jet velocity and the line of sight at some constant distance from the core, which should be manifest as long-term quasi-periodic variability of the radiation flux over the entire observed range of the electromagnetic spectrum of the blazar 0716+714. The differences in the quasi-periods for the variations of PA in (Bach et al 2005;Lister et al 2013) and of the radio- (Raiteri et al 2003;Bychkova et al 2015;Bach et al 2005;Liu et al 2012) and optical (Raiteri et al 2003) fluxes can most simply be explained in the jet geometry considered if the radiation in different spectral ranges is emitted at different distances from the jet apex. This spatial separation of regions radiating at different frequencies can arise due to synchrotron self-absorption in the jet or the energy losses of the radiating electrons.…”

“…Thus, the flux variability at low frequencies is delayed compared to the variability at higher frequencies. Analyses of long-term series of observations reveal different quasi-periods 1 for the long-term optical (≈ 3.3 yrs (Raiteri et al 2003)) and radio (5.5−6 yrs (Raiteri et al 2003;Bychkova et al 2015;Liu et al 2012) variability, and also for variations in the position angle of the inner jet PA in (≈ 11 yrs Lister et al (2013)).…”

Radio and optical intra-day variability observations of five blazars

“…(1) (2) (3) (4) (5) (6) (7) (8) the inner jet, which is suggestive of a helical jet (Liu et al 2012c). The VLBI jet-position angle and the γ rays are also correlated, which suggests that radio waves and γ rays are emitted on the same helical filament, which rotates with the jet (Rani et al 2014), Rani et al (2015) further state that "our analysis favours the major optical/γ-ray flares in S5 0716 + 714 being produced upstream of the 7 mm VLBI core".…”