New evidence for Dicke's superradiance in the 6.7 GHz methanol spectral line in the interstellar medium

TL;DR

This paper provides new observational evidence for superradiance in the 6.7 GHz methanol spectral line in star-forming regions, showing how it explains rapid flux flares and asymmetric light curves as a more efficient energy release mechanism than masers.

Contribution

It demonstrates that superradiance occurs in interstellar methanol masers and explains observed rapid flares through changes in radiative pumping and population densities.

Findings

Superradiance explains fast flux rise times and asymmetric light curves.

Threshold population densities trigger a switch from maser to superradiance.

Superradiance results in intense, short-duration radiation bursts.

Abstract

We present new evidence for superradiance in the methanol 6.7 GHz spectral line for three different star-forming regions: S255IR-NIRS3, G24.329+0.144, and Cepheus A. Our analysis shows that some of the intensity flares exhibiting fast flux rise times and asymmetric light curves reported in these sources can naturally be explained within the context of superradiance. When a threshold for the inverted population column density is exceeded in a maser-hosting region, the radiation mode switches from one regulated by stimulated emission (maser) to superradiance. Superradiance, as a more efficient energy release mechanism, manifests itself through strong bursts of radiation emanating from spatially compact regions. Elevated inverted population densities and the triggering of superradiance can be due to a change in radiative pumping. Here, we show that an increase in the pump rate and the inverted population density of only a factor of a few results in a significant increase in radiation. While the changes in the pump rate can take place over a few hundred days, the rise in radiation flux density when superradiance is initiated is drastic and happens over a much shorter time-scale.