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High mass stars play an important role in the Interstellar Medium, but muchremains to be known about their formation. Class I methanol masers may beunique tracers of an early stage of high mass star formation, and a betterunderstanding of such masers will allow them to be used as more effectiveprobes of the high mass star forming process. We present an investigation ofthe long-term variability of Class I methanol masers at 44 GHz toward the highmass star forming region DR21(OH). We compare observations taken in 2017 to2012 and also to 2001 data from the literature. A total of 57 maser spots werefound in the 2017 data, with center velocities ranging between -8.65 km/s to+2.56 km/s. The masers are arranged in a western and an eastern lobe with twoarcs in each lobe that look like bowshocks, consistent with previousobservations. The general trend is an increase in intensity from 2001 to 2012,and a decrease from 2012 to 2017. Variability appears to be more prevalent inthe inner arc of the western lobe than in the outer arc. We speculate that thismay be a consequence of episodic accretion, in which a later accretion eventhas resulted in ejection of material whose shock reached the inner arc at somepoint in time after 2001. We conclude that class I methanol masers are variableon long timescales (of the order of 5-10 years).

Long-term variability of Class I methanol masers in the high mass star forming region DR21(OH)