Time Variation of Rotation Measure Gradient in 3C 273 Jet

TL;DR

This study confirms a transverse Faraday rotation measure gradient in the 3C 273 jet, observes its time variation over 7 years, and suggests a helical magnetic field as its origin, providing insights into jet magnetic structures.

Contribution

It provides the first evidence of time variation in the RM gradient in the 3C 273 jet, supporting the helical magnetic field model.

Findings

RM gradient persists over 20 mas in the jet

RM varies over a 7-year period at the same jet location

Foreground media are ruled out as the RM origin

Abstract

The existence of a gradient in the Faraday rotation measure (RM) of the quasar 3C 273 jet is confirmed by follow-up observations. A gradient transverse to the jet axis is seen for more than 20 mas in projected distance. Taking account of the viewing angle, we estimate it to be more than 100 pc. Comparing to the distribution of the RM in 1995, we detect a time variation of it at the same distance from the core over 7 yr. We discuss the origin of the Faraday rotation based on this rapid time variation. We rule out foreground media such as a narrow-line region, and suggest a helical magnetic field in the sheath region as the origin of this gradient of the RM.