DICKE’S SUPERRADIANCE IN ASTROPHYSICS. II. THE OH 1612 MHz LINE

Abstract

We apply the concept of superradiance that was introduced by Dicke in 1954 to the OH molecule 1612 MHz spectral line, which is often used for the detection of masers in the circumstellar envelopes of evolved stars. Because the detection of 1612 MHz OH masers in the outer shells of envelopes of these stars implies the existence of a population inversion and a high level of velocity coherence, and that these are two necessary requirements for superradiance, we investigate whether superradiance can also happen in these regions. Superradiance is characterized by high-intensity, spatially compact, burst-like features taking place over timescales on the order of seconds to years, depending on the size and physical conditions present in the regions harboring such sources of radiation. Our analysis suggests that superradiance provides a valid explanation for previous observations of intensity flares detected in that spectral line for the U Orionis Mira star and the IRAS 18276-1431 preplanetary nebula.

Triggered superradiance and fast radio bursts

“…In previous works on SR, whether dealing with star-forming regions (Rajabi & Houde 2017), the surroundings of evolved stars (Rajabi & Houde 2016b) or FRBs , we consistently focused on situations where SR is initiated when the inversion level is high enough to bring the column density nL of the inverted population (n = N/(AL)) above the critical threshold (nL) crit where the time-scale of SR…”

A living theory catalogue for fast radio bursts

“…The aim is to explain FRBs using the atomic interactions in galaxies. DSR can occur in astrophysical settings (Rajabi and Houde, 2016), provided: the collection of atoms is inverted (to wit, a majority of atoms exist in higher excited states than the minority); the velocity coherence is high; and the non-coherent relaxation mechanisms occur on a timescale larger than the delay time. If one models the ISM as a cylinder of atoms, the predicted DSR emission power and timescale can fit FRB data (Houde et al, 2018).…”

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

“…Two of the necessary conditions for SR, i.e., population inversion and velocity coherence among emitters, motivated the search for SR in masing regions where these conditions are known to be met. Accordingly, evidence for SR was so far found for the methanol 6.7 GHz and water 22 GHz spectral lines in star-forming regions (Rajabi & Houde 2017) and E-mail: f3rajabi@uwaterloo.ca † E-mail: mhoude2@uwo.ca for the OH 1612 MHz line in the circumstellar envelope and environment of evolved stars (Rajabi & Houde 2016b). In all these cases, observed variations in the shape of the lightcurves (e.g., damped oscillatory behavior) in some velocity components or significant flux density increases over relatively short time-scales are naturally accounted for within the context of SR.…”

“…However, it had remained unknown to the astronomy community until its recent applications to the interstellar medium (ISM) (Rajabi & Houde 2016a,b;Rajabi 2016;Rajabi & Houde 2017). SR, a coherent radiation mechanism, can provide explanation for strong radiation bursts taking place over a wide domain of time-scales ranging from sub-seconds (Mathews 2017;Houde et al 2019;Houde, Mathews & Rajabi 2018) to several years (Rajabi & Houde 2016b).…”