Polarisation of Class II Methanol Masers

TL;DR

This study presents the first polarisation measurements of 6.7 GHz methanol masers using a new calibration technique, revealing linear polarisation levels and estimating magnetic field strengths through Zeeman splitting.

Contribution

Introduces a novel calibration method for spectral line polarisation observations and provides the first polarisation data for several methanol masers.

Findings

Linear polarisation at 5-10% in most sources

First polarisation measurements of these masers

Estimated magnetic field strength of 35+/-7 mG in G9.62+0.20

Abstract

We have used the University of Tasmania Mt Pleasant 26m radio telescope to investigate the polarisation characteristics of a sample of strong 6.7 GHz methanol masers, the first spectral line polarisation observations to be undertaken with this instrument. As part of this process we have developed a new technique for calibrating linear polarisation spectral line observations. This calibration method gives results consistent with more traditional techniques, but requires much less observing time on the telescope. We have made the first polarisation measurements of a number of 6.7 GHz methanol masers and find linear polarisation at levels of a few - 10% in most of the sources we observed, consistent with previous results. We also investigated the circular polarisation produced by Zeeman splitting in the 6.7 GHz methanol maser G9.62+0.20 to get an estimate of the line of sight magnetic field strength of 35+/-7 mG.