# VLBI Monitoring of the Sub-parsec-scale Jet in the Radio Galaxy 3C 66B at 22 GHz

## TL;DR

This study uses VLBA observations at 22 GHz over four years to analyze the proper motion and flux variations of the jet in galaxy 3C 66B, revealing stationary inner knots and potential jet structure complexities.

## Contribution

First detailed VLBI monitoring of 3C 66B's jet at 22 GHz over multiple years, highlighting stationary features and flux behavior, suggesting a complex jet structure.

## Key findings

- Inner knots are nearly stationary.
- No flux variation in the core at 22 GHz.
- Jet appears slower at higher frequency.

## Abstract

We present measurements of proper motion of the sub-parsec scale jet at 22 GHz in the nearby FR I galaxy 3C 66B. Observations were made using the VLBA at six epochs over four years. A phase-referencing technique was used to improve the image quality of the weak and diffuse jet components. We find that the inner knots are almost stationary, though one of them was expected to be detected with the apparent speed of 0.2 mas/yr according to 8 GHz monitoring at the same observation epochs. Clear flux variations are not observed in the core at 22 GHz, in contrast, clear flux enhancement is observed in the core at 8 GHz. We discussed that this can be explained, if the jet has helical structure, that the viewing angle of the jet between 8 and 22 GHz differs by a few degree in case the jet direction is almost along our line of sight. Although these results may imply the existence of a two-zone jet, which has been suggested in certain radio galaxies, it cannot explain the fact that the jet at the higher frequency jet is slower than that at the lower frequency.