Mid-Infrared and Maser Flux Variability Correlation in Massive Young Stellar Object G036.70+00.09

TL;DR

This study reveals correlated flux variability in a massive young stellar object across mid-infrared and maser emissions over different timescales, supporting the link between maser activity and accretion disk processes.

Contribution

First to report simultaneous MIR and maser flux variability correlation in a MYSO over year-long and day-long timescales, suggesting a connection to accretion disk dynamics.

Findings

Confirmed stochastic year-long MIR variability without color change.

Detected periodic methanol maser flux with 53-day cycle.

Established correlation between MIR and maser flux variations.

Abstract

We present the discovery of the simultaneous flux variation of a massive young stellar object (MYSO) G036.70+00.09 (G036.70) both in the maser emission and mid-infrared (MIR;$\lambda=3$--$5$~$\mu$m) bands. Utilizing the ALLWISE and NEOWISE archival databases covering a long time span of approximately 10 years with a cadence of 6 months, we confirmed that G036.70 indicates a stochastic year-long MIR variability with no signs of the WISE band color change of W1 (3.4~$\mu$m) $-$W2 (4.6~$\mu$m). Cross-matching the MIR data set with the high-cadence 6.7~GHz class II methanol maser flux using a Hitachi 32-m radio telescope that discovered its periodicity in the methanol maser of 53.0--53.2 days, we also determine the flux correlations between the two bands at two different timescales, year-long and day-long, both of which have never been reported in MYSOs except when they are in a state of the accretion burst phase. The results of our study support the scenario that a class II methanol maser is pumped up by infrared emission from accreting disks of MYSOs. We also discuss the possible origins of MIR and maser variability. To explain the two observed phenomena, a stochastic year-long MIR variability with no signs of significant color change and maser-MIR variability correlation, change in mass accretion rate and line-of-sight extinction because of nonaxisymmetric dust density distribution in a rotating accretion disk are possible origins. Observations through spectroscopic monitoring of accretion-related emission lines are essential for determining the origin of the observed variability in G036.70.