Observations of the Bursting Activity of the 6.7GHz Methanol Maser in G33.641-0.228

TL;DR

This study reports the detection and analysis of five bursting events in the 6.7 GHz methanol maser of G33.641-0.228 over three years, suggesting magnetic energy release as a possible cause.

Contribution

First detailed observation of bursting variability in methanol maser G33.641-0.228, proposing a solar-flare-like magnetic energy release mechanism.

Findings

Five bursts detected over 294 days

Bursts occur approximately every 59 days on average

Burst energy is much smaller than the source's total luminosity

Abstract

We have observed bursting variability of the 6.7 GHz methanol maser of G33.641-0.228. Five bursts were detected in the observation period of 294 days from 2009 to 2012. The typical burst is a large flux density rise in about one day followed by a slow fall. A non-typical burst observed in 2010 showed a large and rapid flux density enhancement from the stable state, but the rise and fall of the flux density were temporally symmetric and a fast fluctuation continued 12 days. On average, the bursts occurred once every 59 days, although bursting was not periodic. Since the average power required for causing the burst of order of 10^21 Js^-1 is far smaller than the luminosity of G33.641-0.228, a very small fraction of the source's power would be sufficient to cause the burst occasionally. The burst can be explained as a solar-flare like event in which the energy is accumulated in the magnetic field of the circumstellar disk, and is released for a short time. However, the mechanism of the energy release and the dust heating process are still unknown.