Very Large Array Detection of the 36 GHz Zeeman Effect in DR21W Revisited

TL;DR

This study revisits the detection of the Zeeman effect in the 36 GHz methanol maser line in DR21W, correcting previous instrumental errors and establishing a new upper limit for the magnetic field strength.

Contribution

The paper provides a revised measurement of the magnetic field in DR21W by addressing instrumental issues in earlier observations, offering more accurate constraints.

Findings

Previous Zeeman detection was instrumental artifact.

New data sets a 3 sigma limit of -4.7 to +0.4 mG for magnetic field.

Instrumental effects can significantly impact Zeeman measurements.

Abstract

We report on the observation of the 36 GHz methanol maser line in the star forming region DR21W to accurately measure the Zeeman effect. The reported Zeeman signature by Fish et al. (2011) became suspicious after an instrumental effect was discovered in the early days of the Very Large Array Wide-band Digital Architecture (WIDAR) correlator commissioning. We conclude that the previously reported magnetic field strength of 58 mG ((1.7 Hz/mG)/z) is instrumental in nature and thus incorrect. With the improved performance of the array, we now deduce a 3 sigma limit of -4.7 to +0.4 mG ((1.7 Hz/mG)/z) for the line-of-sight component of the magnetic field strength in DR21W.