Magnetic Field Structure in the Parsec Scale Jet of 3C273 from Multifrequency VLBA Observations

TL;DR

This study uses multifrequency VLBA observations of 3C273 to analyze the magnetic field structure and energy distribution in its parsec-scale jet, revealing a magnetic field gradient and energy dominance variations.

Contribution

It introduces a new model-fitting method to derive spectra and magnetic fields in the jet without assuming equipartition, providing detailed magnetic field measurements.

Findings

Magnetic field density of about 1 Gauss in the core.

Magnetic energy dominates over electron energy in the core.

A transverse magnetic field gradient correlates with velocity structure.

Abstract

We present first results from a multifrequency VLBA observations of 3C273 in 2003. The source was observed simultaneously at 5.0, 8.4, 15.3, 22.2, 43.2 and 86.2 GHz, and from this multifrequency data set, spectra of 16 emission features in the parsec scale jet were carefully constructed by using a new model-fitting based method. The measured spectra and sizes of the emission features were used to calculate the magnetic field density and the energy density of the relativistic electrons in the different parts of the parsec scale jet, independent of any equipartition assumption. We measure magnetic field density of an order of 1 Gauss in the core. The magnetic energy density in the core dominates over that of the relativistic electrons, while in the downstream region our data are roughly consistent with an equipartition. A strong gradient in the magnetic field density across the jet width, coincident with a transverse velocity structure at about 1.5 mas from the core, was found: the slower superluminal component B2 on the northern side of the jet has a magnetic field density two orders of magnitude lower than the faster southern components B3 and B4.