The Environment of the Strongest Galactic Methanol Maser

Abstract

The high-mass star-forming site G009.62+00.20 E hosts the 6.7 GHz methanol maser source with the greatest flux density in the Galaxy which has been flaring periodically over the last 10 yr. We performed high-resolution astrometric measurements of the CH<SUB>3</SUB>OH, H<SUB>2</SUB>O, and OH maser emission and 7 mm continuum in the region. The radio continuum emission was resolved in two sources separated by 1300 AU. The CH<SUB>3</SUB>OH maser cloudlets are distributed along two north-south ridges of emission to the east and west of the strongest radio continuum component. This component likely pinpoints a massive young stellar object which heats up its dusty envelope, providing a constant IR pumping for the Class II CH<SUB>3</SUB>OH maser transitions. We suggest that the periodic maser activity may be accounted for by an independent, pulsating, IR radiation field provided by a bloated protostar in the vicinity of the brightest masers. We also report the discovery of an elliptical distribution of CH<SUB>3</SUB>OH maser emission in the region of periodic variability.