Modelling of the multi-transition periodic flaring in G9.62+0.20E

TL;DR

This paper models periodic flaring in methanol and OH maser lines in G9.62+0.20E using Maxwell-Bloch equations, showing that superradiance explains the observed variations and peculiar behaviors in the spectral features.

Contribution

It introduces a superradiance-based model within Maxwell-Bloch equations to explain complex maser flaring behaviors in star-forming regions.

Findings

Superradiance explains variations in flare durations.

Partial quenching of population inversion accounts for peculiar spectral features.

Model reproduces observed flaring behaviors across multiple transitions.

Abstract

We present detailed modeling of periodic flaring events in the 6.7 GHz and 12.2 GHz methanol lines as well as the OH 1665 MHz and 1667 MHz transitions observed in the G9.62+0.20E star-forming region. Our analysis is performed within the framework of the one-dimensional Maxwell-Bloch equations, which intrinsically cover the complementary quasi-steady state maser and transient superradiance regimes. We find that the variations in flaring time-scales measured for the different species/transitions, and sometimes even for a single spectral line, are manifestations of and are best modeled with Dicke's superradiance, which naturally accounts for a modulation in the duration of flares through corresponding changes in the inversion pump. In particular, it can explain the peculiar behaviour observed for some features, such as the previously published result for the OH 1667 MHz transition at $v_\mathrm{lsr}=+1.7$ km s$^{-1}$ as well as the methanol 6.7 GHz line at $v_\mathrm{lsr}=-1.8$ km s$^{-1}$, through a partial quenching of the population inversion during flaring events.