Methanol Line Diagnostics of Post-burst Physical Evolution in the High-mass Episodic Accretion Source G358.93−0.03

Abstract We report multi-epoch Atacama Large Millimeter/submillimeter Array Band 5–7 observations of the high-mass episodic-accretion burst source G358.93−0.03, covering (sub-)millimeter CH 3 OH masers, quasi-thermal lines, and continuum from 2019 April to 2022 January. Five new CH 3 OH maser transitions (189.369, 220.401, 241.043, 293.464, and 330.794 GHz) were detected, all coincident with the brightest continuum core MM1. Together with nine previously known sub-millimetre masers, they exhibit a rapid intensity decline on 3 month timescales from 2019 April to July. In 2019 April, the maser spots form a ring-like pattern, matching the morphology of centimeter-wavelength counterparts observed in previous studies. Rotation diagram analysis of quasi-thermal CH 3 OH lines reveals pronounced post-burst evolution in the gas envelopes of MM1 and MM3: both cores were heated due to the heat wave propagation induced by the episodic accretion from MM1 in 2019 October. These results establish that episodic accretion bursts in massive protostars trigger rich (sub)millimeter maser activity and drive radiative heat waves across their natal environments.