DICKE’S SUPERRADIANCE IN ASTROPHYSICS. I. THE 21 cm LINE

Abstract

We have applied the concept of superradiance introduced by Dicke in 1954 to astrophysics by extending the corresponding analysis to the magnetic dipole interaction characterizing the atomic hydrogen 21 cm line. Although it is unlikely that superradiance could take place in thermally relaxed regions and that the lack of observational evidence of masers for this transition reduces the probability of detecting superradiance, in situations where the conditions necessary for superradiance are met (i.e., close atomic spacing, high velocity coherence, population inversion, and long dephasing time-scales compared to those related to coherent behavior), our results suggest that relatively low levels of population inversion over short astronomical length-scales (e.g., as compared to those required for maser amplification) can lead to the cooperative behavior required for superradiance in the ISM. Given the results of our analysis, we expect the observational properties of 21-cm superradiance to be characterized by the emission of high intensity, spatially compact, burst-like features potentially taking place over short periods ranging from minutes to days.

Triggered superradiance and fast radio bursts

“…As was the case in our previous applications of SR to astrophysics (Rajabi & Houde 2016a,b;Rajabi & Houde 2017;Rajabi 2016;, our SR samples are assumed to have a cylindrical geometry of length L λ, with λ the wavelength of radiation. The radius of a sample is constrained by imposing a Fresnel number of unity (i.e., the cross section of the cylinder is given by A = λL), a necessary condition for preserving phase coherence along the length of the sample (Gross & Haroche 1982;Rajabi & Houde 2017).…”

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

“…Dicke's superradiance (SR; Dicke 1954) has been the subject of intensive research in the physics community for decades (Gross & Haroche 1982;Benedict et al 1996). 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).…”

Generalisation of the Menegozzi & Lamb Maser Algorithm to the Transient Superradiance Regime

“…The MB equations are the starting point of Menegozzi & Lamb (1978) and of our present work. A derivation of the MB equations as a valid representation of transient SR processes (under reasonable approximations) can be found in the literature (Arecchi & Courtens 1970;MacGillivray & Feld 1976;Gross & Haroche 1982;Andreev 1990;Benedict et al 1996;Rajabi & Houde 2016a). We turn now to discuss the MB equations over a velocity distribution, with the objective of constructing a numerically efficient algorithm for solving them in the transient SR regime.…”

“…There are three common methods for modelling the maser action across wide incoherent velocity distributions: first, by a theory of rate-balanced excitation and de-excitation of velocity sub-populations, with accompanying equations of radiative transfer (Elitzur 1992); second, by the master equation describing the evolution of the quantum mechanical density operator (Goldreich & Kwan 1974;Menegozzi & Lamb 1978;Gray 2012); and third, by the Heisenberg equations describing the time evolution of expectation values of the population inversion, polarisation, and field operators within the Heisenberg picture of QED (Gross & Haroche 1982;Rajabi & Houde 2016a). The latter two methods lead to the velocity dependent MB equations.…”