Polarization Observations of a Sample of 6.7 GHz Methanol Masers

TL;DR

This study reports polarization measurements of 6.7 GHz methanol masers in star-forming regions, revealing variability in polarization and Zeeman splitting over time, likely due to magnetic field changes.

Contribution

First comprehensive polarization survey of methanol masers across multiple epochs, highlighting temporal variations and magnetic field influences.

Findings

Two-thirds of sources show methanol masers, including one new detection.

Linear polarization ranges from 0 to 15%, circular from 0 to ±9%.

Zeeman splitting varies over time and correlates with polarization changes.

Abstract

Spectra of 6.7 GHz methanol masers from 21 pointings of known star-forming regions are reported. The C-band observations, using the Green Bank Telescope in full Stokes mode, have measured how polarization properties vary across the maser profiles in each spectrum and vary between different epochs of observation. Two-thirds of the sources are observed to have 6.7 GHz methanol masers, including one new detection (G240.316+0.071). Linear polarization is in the range 0 to 15% and circular polarization 0 to $\pm$9%, in line with previously reported values. The only instances where polarization is not observed is when these polarization ranges are below 3$\sigma$ detection limits. Zeeman splitting is observed in several sources, with splitting values derived from velocity separation between RCP and LCP components via Gaussian fitting. These values are seen to change with time and appear to correspond to changes in the linear and circular polarization. The polarization properties varying across the spectra and changing with time are most likely due to variations in the magnetic fields.