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11th of January 2022
ATCA observations of a flaring methanol maser
by McCarthy et al.
McCarthy et al. have performed a molecular line search toward the flaring 6.7-GHz methanol masers G24.33+0.13 and G359.62–0.24, associated with high-mass star-formation regions, using the Australia Telescope Compact Array. Methanol masers are pumped through either collisional or radiative interactions, which divides them into class I and class II respectively McCarthy et al. present spectra of the 6.7-GHz class II methanol and 22.2-GHz water masers toward these sources and compare their results with other recent flaring events observed in these sources. They also detected the fourth example of a 23.4-GHz class I methanol maser, and the eleventh example of a 4.8-GHz formaldehyde maser toward G24.33+0.13. In addition, they observe the previously detected ammonia (3,3) emission and report upper limits on the presence of various other cm-wavelength methanol, ammonia and OH transitions. Their results are consistent with the flaring of G24.33+0.13 being driven by a variable accretion rate in the host high-mass young stellar object.

The figure above shows a comparison between 6.7-GHz class II maser spectra toward G24.33+0.13 during the 2019 November flaring epoch and the quiescent 2021 February epoch. During the flare, the spectral profile is dominated by two primary peaks at velocities of 113.4 and 115.3 km/s (with respect to the Local Standard of Rest), with several weaker components (factor of ∼6 lower flux density) distributed across the rest of the velocity range. In 2021 February (17 months after the flare was detected), the flux density of these two peaks has decreased by a factor of ∼20, with the 110 km/s feature becoming the brightest maser component. In addition to the two flaring features dimming, there is a general decrease in flux density across all maser components in the second epoch. The paper will be published in Monthly Notices of the Royal Astronomical Society.

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