Incorporate and disentangle an external Faraday-rotating sheath

Incorporate an external magnetized Faraday-rotating sheath surrounding the AGN jet and disentangle its position-dependent Faraday-depth contribution from the intrinsic Faraday and polarization signatures produced by the jet’s internal helical magnetic field.

Background

The three-dimensional AGN-jet model assumes that synchrotron emission and Faraday rotation occur within the same cylindrical plasma and therefore omits an external magnetized sheath surrounding the jet. The paper notes that such a sheath can contribute a Faraday rotation comparable to that of the jet body, producing position-dependent Faraday-depth offsets and gradients along individual lines of sight.

Because an external sheath could partially mask, enhance, or mimic the intrinsic signatures of the helical magnetic field, future work must model the sheath and determine how to separate its contribution from the internal field. This would reduce an important degeneracy in interpreting observed Faraday Dispersion Functions of AGN jets.

References

The ratio $\sigma_{\rm RM}/|\mathrm{RM}|$ would additionally inform whether the turbulent or ordered component of the magnetic field dominates; we defer this analysis to a future study with expanded frequency coverage~\citep{burn1966}.

— First Detection of Radio Polarization During Jet Formation in the Changing-Look AGN 1ES 1927+654  (2609.09539 - Shuvo et al., 8 Sep 2026) in Section 3.3, “Magnetic Field Strength”

Incorporating an external Faraday-rotating sheath, and disentangling its contribution from that of the internal field, is therefore an important extension that we leave to future work.

— Probing the Three-Dimensional Structure of a Jet with Faraday Tomography  (2608.24490 - Gull et al., 25 Aug 2026) in Discussion and Summary, Section 5, paragraph beginning “The present model assumes that synchrotron emission and Faraday rotation arise within the same cylindrical plasma”