Periodic 6.7 GHz $\mathrm{CH_3OH}$ maser emission in G353.273+0.641: First candidate for a pulsating high-mass protostar

TL;DR

This study reports a 309-day periodicity in 6.7 GHz methanol maser emission from a high-mass protostar, suggesting pulsation as a potential origin, supported by correlated infrared variability and theoretical models of protostellar evolution.

Contribution

It presents the first candidate for a pulsating high-mass protostar based on long-term maser monitoring and analysis of periodic flux variations.

Findings

Detected 309-day periodicity in maser emission.

Correlated infrared flux variations suggest luminosity response.

Maser light curve resembles pulsating variable star profiles.

Abstract

We report on the periodic flux variations in the 6.7 GHz $\mathrm{CH_3OH}$ maser associated with the high-mass protostar G353.273+0.641, based on 13 yr of monitoring mainly by the Hitachi 32 m telescope. We identified a periodicity of 309 days based on a nearly complete light curve, with 833 epochs every few days. A strong correlation is found between the maser and the mid-infrared fluxes at 3.4 and 4.6 $\mu$m observed by NEOWISE during these periods, suggesting that the maser emission responds to variations in the protostellar luminosity. The average profile of the maser light curve is asymmetric and shows a steep drop in intensity just before the brightening, resembling that of some pulsating variable stars. Assuming a protostellar pulsation as the origin of maser periodicity, the observed period implies a cool and highly bloated, red supergiant-like structure. Such a bloated structure is consistent with a theoretical model of protostellar evolution under high accretion rates. The inferred protostellar parameters are broadly consistent with the theoretical model of pulsational instability during the early phase of high-mass star formation. However, a periodic accretion scenario caused by an unresolved compact protobinary cannot be completely ruled out. Several irregular peaks that deviate from the periodicity may result from episodic accretion phenomena or jet-launching events independent of the protostellar pulsation. Extremely high-resolution imaging with next-generation interferometers such as the ngVLA will provide a conclusive test for both the protostellar pulsation and the binary accretion scenarios.