# Jet Kinematics of the Quasar 4C +21.35 from Observations with the KaVA Very Long Baseline Interferometry Array

## TL;DR

This study tracks the motion of jet components in quasar 4C +21.35 using KaVA VLBI observations, revealing high apparent speeds, correlations with gamma-ray flares, and differences with other arrays, advancing understanding of jet dynamics.

## Contribution

First detailed VLBI kinematic analysis of 4C +21.35 using KaVA, highlighting resolution-dependent jet feature identification and jet speed variations.

## Key findings

- Jet components reach apparent speeds up to 14.4c.
- Jet speeds increase with distance from the core.
- Discrepancies between KaVA and other VLBI data suggest resolution effects.

## Abstract

We present the jet kinematics of the flat spectrum radio quasar (FSRQ) 4C +21.35 using time-resolved KaVA very long baseline interferometry array radio maps obtained from September 2014 to July 2016. During two out of three observing campaigns, observations were performed bi-weekly at 22 and 43 GHz quasi-simultaneously. At 22 GHz, we identified three jet components near the core with apparent speeds up to (14.4+/-2.1)c. The timing of the ejection of a new component detected in 2016 is consistent with a gamma-ray flare in November 2014. At 43 GHz, we found four inner jet (<3 mas) components with speeds from (3.5+/-1.4)c to (6.8+/-1.5)c. Jet component speeds tend to be higher with increasing distances from the core. We compared our data with archival Very Long Baseline Array (VLBA) data from the Boston University (BU) 43 GHz and the Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE) 15.4 GHz monitoring programs. Whereas MOJAVE data and our data are in good agreement, jet speeds obtained from the BU Program data in the same time period are about twice as high as the ones we obtain from the KaVA data. The discrepancy at 43 GHz indicates that radio arrays with different angular resolution identify and trace different jet features even when the data are obtained at the same frequency and at the same time. The flux densities of jet components decay exponentially, in agreement with a synchrotron cooling time scale of about 1 year. Using known electron Lorentz factor values (about 9,000), we estimate the magnetic field strength to be around 1-3 micro-Tesla. When adopting a jet viewing angle of 5 degrees, the intrinsic jet speed is of order 0.99c.