Studies of stationary features in jets: 3C 279 quasar I. On-sky scattering and dynamics

TL;DR

The study analyzes the quasi-stationary component in the 3C 279 jet using 27 years of 15 GHz VLBA MOJAVE data to detect relativistic transverse waves and quantify their properties. By disentangling intrinsic QSC motion from core displacements through smoothing and reversal analysis, the authors estimate a mean QSC speed of about 10c and infer a transverse-wave Lorentz factor near 60 with a small inclination (~0.2 degrees). They find a jet-direction change of ~21 degrees over the observation period and an apparent QSC cone angle of ~15.7 degrees (deprojected ~0.28 degrees), implying substantial transverse wave amplitudes (~0.06 mas) and a wave frequency near 0.5 yr⁻¹. The results, in comparison with BL Lac, show stronger magnetic-energy-dominated transverse waves in 3C 279 and demonstrate that QSC dynamics offer a robust diagnostic for characterizing relativistic waves in blazar jets, with implications for jet magnetization and geometry.

Abstract

A recent study on the dynamics of the quasi-stationary component (QSC) in the jet of BL~ Lacertae highlighted its significance in evaluating the physical properties of relativistic transverse waves in the parsec-scale jet. Motivated by this finding, we selected a different type of blazar, the flat-spectrum radio quasar (FSRQ) 3C~279, which hosts a QSC at an angular median distance of 0.35~mas from the radio core, as revealed by 27 years of VLBA monitoring data at 15~GHz. We investigate the positional scatter and dynamics of a QSC in the 3C~279 jet, aiming to detect the presence of a relativistic transverse wave and estimate its characteristics. We employ an analytical statistical method to estimate the mean intrinsic speed of the QSC, while moving average and refinement methods are used to smooth its trajectory. Analysis of the QSC position scatter shows that the jet axis change its direction by about $21^{\circ}$ over 27 years and jet mean intrinsic full opening angle is $\approx 0.30^{\circ} \pm 0.03^{\circ}$. The apparent displacement vectors of the QSC exhibit strong asymmetry and anisotropy along the jet direction, indicating pronounced anisotropic displacements of the core along the jet axis. We estimated the mean intrinsic speed of the QSC to be superluminal, $\overline{β_{\rm s}} \approx 10$ in units of the speed of light, which, within the framework of the seagull-on-wave model, is interpreted as evidence for a relativistic transverse wave propagating through the QSC. Analysis of the reversing trajectory of the QSC enables the classification and characterisation of reversal patterns, which, in turn, allows the determination of key transverse wave parameters such as frequency, amplitude, inclination angle, and magnetic energy of the wave (abbrev.).

Figures (12)

• Figure 1: Scatter of 161 positions of QSC on the sky plane. The sizes of the crosses correspond to QSC position errors in the directions toward of and across the core. The radio core is marked by a filled circle at position (0,0), and the median position of the QSC scattering is marked by a red plus sign. The dashed red line is the central axis of the jet, which connects the median positions of the QSC and the core. The dashed green lines represent the linear fit of the cone lines.
• Figure 2: Variation in QSC position angle with time. The dashed red line is the position angle of the jet central axis, ${\rm PA}_{\rm jet} = -138\degr$, and the blue line is a linear fit to the changes in QSC position angles with time.
• Figure 3: Positions of the QSC within the six time intervals, 1995.57$-$1999, 1999$-$2002, 2002$-$2005.71, 2005.71$-$2010.9, 2013.24$-$2020 and 2020$-$2022.22. The blue plus sign is the median position of the QSC positions within the given time interval. The dashed blue line is the axis of the jet connecting the core and the median position of QSC. The dashed red line is the central axis of the jet, connecting the median position of QSC over the entire observation period 1995.57$-$2022.22 and the core. The sizes of the crosses correspond to QSC position errors in the directions toward of and across the core.
• Figure 4: Distributions of 160 apparent QSC displacements (light blue area) and their uncertainties (transparent).
• Figure 5: Apparent QSC displacements as a function of the observation time interval. The $1\sigma$ uncertainties of the apparent displacements are presented. Apparent displacements with high relative errors $\varepsilon_{\rm r} > 0.5$ are indicated in red. The dashed vertical line indicates the median observational interval of 37 days.