# An oversized magnetic sheath wrapping around the parsec-scale jet in 3C 273

**Authors:** M. M. Lisakov, E. V. Kravchenko, A. B. Pushkarev, Y. Y. Kovalev, T. K. Savolainen, M. L. Lister  
**arXiv:** [2102.04563](https://arxiv.org/abs/2102.04563)  
**Date:** 2021-02-08  
**Summary page:** https://www.summarizepaper.com/en/paper/2102.04563v1/

## Key points

- Recent studies show that some Active Galactic Nuclei (AGN) exhibit gradients of the Faraday Rotation Measure (RM) transverse to their parsec-scale jet direction.
- This is likely due to a magnetized sheath wrapped around the jet, causing Faraday rotation.
- Researchers observed significant changes in the jet RM towards negative values in 3C 273, which could be explained by a swing of the parsec-scale jet direction.
- Researchers developed an oversized sheath model for the jet-sheath system in 3C 273 with a derived wide jet full intrinsic opening angle $\alpha_\mathrm{int}=2.1^\circ$ and magnetic field strength $B_{||}=3$ $\mu$G and thermal particle density $N_\mathrm{e}=125~\mathrm{cm}^{-3}$ at the wide jet--sheath boundary 230 pc downstream (deprojected) from its beginning.
- The model brings together both long-term RM evolution and changes in apparent jet direction on parsec-scales, providing new insights into how AGNs evolve over time and interact with their surrounding environments.
- The findings have important implications for our understanding of AGN evolution and their interactions with their environment.

## Summary

Recent studies have shown that several Active Galactic Nuclei (AGN) exhibit gradients of the Faraday Rotation Measure (RM) transverse to their parsec-scale jet direction. This phenomenon is likely due to a magnetized sheath wrapped around the jet, causing Faraday rotation. In the case of 3C 273, using Very Long Baseline Array multi-epoch observations at 5, 8 and 15 GHz in 2009--2010, researchers observed that the jet RM had changed significantly towards negative values compared with previous observations. These changes could be explained by a swing of the parsec-scale jet direction which causes synchrotron emission to pass through different portions of the Faraday screen. To further investigate this phenomenon, researchers developed a model for the jet-sheath system in 3C 273 where the sheath was wider than the single-epoch narrow relativistic jet. They presented an oversized sheath model together with a derived wide jet full intrinsic opening angle $\alpha_\mathrm{int}=2.1^\circ$ and magnetic field strength $B_{||}=3$ $\mu$G and thermal particle density $N_\mathrm{e}=125~\mathrm{cm}^{-3}$ at the wide jet--sheath boundary 230 pc downstream (deprojected) from its beginning. Most of the Faraday rotation occurs within the innermost layers of the sheath. The model brings together both long-term RM evolution and changes in apparent jet direction on parsec-scales, providing new insights into how AGNs evolve over time and interact with their surrounding environments. Previous studies have also revealed that AGN jets change their direction on parsec-scales over time (e.g., Savolainen et al. 2006). The findings from this study are important for understanding how AGNs evolve over time and how they interact with their surroundings. The oversized sheath model developed for 3C 273 sheds light on how changes in jet direction can affect Faraday rotation, and may be applicable to other AGNs exhibiting similar phenomena. These findings have important implications for our understanding of AGN evolution and their interactions with their environment.