Exploring the Morphology and Origins of the 4C 38.41 Jet

TL;DR

This study investigates the innermost jet of quasar 4C 38.41 using VLBI data, revealing a semi-parabolic geometry, magnetic field and density profiles, and potential jet precession or instabilities affecting its morphology.

Contribution

It provides detailed measurements of jet geometry, magnetic field, and density profiles, and proposes explanations for the jet's sinusoidal morphology based on precession or instabilities.

Findings

Jet radius follows R ∝ r^{0.7} with a possible geometry break.

Brightness temperature decreases as T_B ∝ r^{-2.1}.

Magnetic field and electron density decrease along the jet as B ∝ r^{-1.5} and n ∝ r^{-1.1}.

Abstract

We study the properties of the innermost jet of the flat spectrum radio quasar 1633+382 (4C~38.41) based on VLBI data from the radio monitoring observations of the Boston University VLBI program at 43~GHz. Analysis of the components suggests a semi-parabolic jet geometry with jet radius $R$ following the relation $R\propto r^{0.7}$ with distance $r$, with indications of a jet geometry break towards a conical geometry. Brightness temperature falls with distance following $T_B\propto r^{-2.1}$. Combining this information, magnetic field and electron densities are found to fall along the jet as $B\propto r^{-1.5}$ and $n\propto r^{-1.1}$ respectively, suggesting that the magnetic configuration in the jet may be dominated by the poloidal component. Our analysis of the jet structure suggests that the innermost jet regions do not follow a ballistic trajectory and, instead, match a sinusoidal morphology which could be due to jet precession from a helical pattern or Kelvin-Helmholtz instabilities.