The Extraordinary Maser Flaring Event in the Massive Protostellar System NGC6334I: Multi-Epoch Milliarcsecond Resolution Investigation of the 6.7-GHz Methanol Masers

We report the first multi-epoch milliarcsecond resolution imaging of the 6.7-GHz class II methanol maser emission associated with the high-mass protocluster system NGC6334I. The observations covered a period of over 10 years in four epochs between March 2010 and March 2020. We confirmed for the first time the emergence of 6.7-GHz methanol maser emission associated with NGC6334I-MM1, which lies north of the previously known sites of class II methanol masers, NGC6334-MM2 and MM3. The new maser emission was located close to the strongest (sub)millimetre source in NGC6334I-MM1, identified as MM1-B, which experienced a sudden increase in intensity in 2015, produced by an episodic accretion event. We are able to compare the location and intensity of the 6.7-GHz methanol maser emission among the epochs before, during, and after the flare, providing new insights into the relationship between maser flares and episodic accretion events in high-mass stars.