Possible magnetic field variability during the 6.7 GHz methanol maser flares of G09.62+0.20

TL;DR

This study monitored the magnetic field in a periodically flaring methanol maser region, finding a stable magnetic field most of the time but a significant change during flare peaks, suggesting complex magnetic or radiative effects.

Contribution

It provides the first detailed measurement of magnetic field variability during methanol maser flares, highlighting potential magnetic or radiative transfer influences.

Findings

Magnetic field remains constant (~11 mG) during most of the flare cycle.

A sharp decrease and possible reversal of Zeeman splitting occurs during flare peaks.

Magnetic or polarization variability may be linked to background amplification or non-Zeeman effects.

Abstract

(Abridged) Recently, the magnetic field induced Zeeman splitting was measured for the strongest known 6.7 GHz methanol maser, which arises in the massive star forming region G09.62+0.20. This maser is one of a handful of periodically flaring methanol masers. The 100-m Effelsberg telescope was used to monitor the 6.7 GHz methanol masers of G09.62+0.20. With the exception of a two week period during the peak of the maser flare, we measure a constant magnetic field of B_||~11+-2 mG in the two strongest maser components of G09.62+0.20 that are separated by over 200 AU. In the two week period that coincides exactly with the peak of the maser flare of the strongest maser feature, we measure a sharp decrease and possible reversal of the Zeeman splitting. The exact cause of both maser and polarization variability is still unclear, but it could be related to either background amplification of polarized emission or the presence of a massive protostar with a close-by companion. Alternatively, the polarization variability could be caused by non-Zeeman effects related to the radiative transfer of polarized maser emission.