The environment of the strongest galactic methanol maser

TL;DR

This study investigates the environment of the strongest galactic methanol maser, revealing its association with a massive young stellar object and proposing a pulsating IR radiation field as the cause of its periodic activity.

Contribution

It provides high-resolution measurements of maser emissions and continuum, and suggests a new model involving a pulsating IR field from a bloated protostar for maser periodicity.

Findings

Radio continuum emission resolved into two sources separated by 1300 AU.

Methanol masers distributed along two ridges around a massive young stellar object.

Discovery of an elliptical distribution of methanol maser emission associated with periodic variability.

Abstract

The high-mass star-forming site G009.62+00.20E hosts the 6.7 GHz methanol maser source with the greatest flux density in the Galaxy which has been flaring periodically over the last ten years. We performed high-resolution astrometric measurements of the CH3OH, H2O, 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 CH3OH 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 CH3OH 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 about the discovery of an elliptical distribution of CH3OH maser emission in the region of periodic variability.