DSR in Galaxies

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Summary Table
Category Progenitor Type Energy Mechanism Emission Mechanism Counterparts References Brief Comments
LF Radio HF Radio Microwave Terahertz Optical/IR X-rays Gamma-rays Gravitational Waves Neutrinos
Other Dicke's Superradiance in Galaxies Both Dicke's Superradiance Spectral line Yes Yes -- -- -- -- -- -- -- http://adsabs.harvard.edu/abs/2018MNRAS.475..514H, http://adsabs.harvard.edu/abs/2018arXiv181004364H --

Definitions: LF Radio (3 MHz to 3 GHz); HF Radio (3 GHz to 30 GHz); Microwave (30 to 300 GHz)

Model Description

Postulated in 1954 and first detected in 1973, Dicke's Superradiance (DSR) has been invoked as one of the few “microphysical” FRB models. The aim is to explain FRBs using molecular interactions in galaxies. DSR can occur in astrophysical settings, provided: the collection of molecules is inverted; the velocity coherence is high; and the non-coherent relaxation (e.g., inelastic collisions) and dephasing (e.g., Doppler broadening) mechanisms occur on a time-scale larger than DSR time-scales. When these conditions are met, the collection of molecules become entangled (i.e., act as a unit instead of independently), which causes the rate of emission and the radiation intensity to be greatly enhanced. Assuming a cylindrical geometry for the collection of molecules partaking in a DSR event, the predicted DSR emission power and time-scale can fit FRB data. This model is additionally appealing since the DSR mechanism can adapt to a wide variety of FRB behaviours, and proposes no new entities/physics. Indeed, the DMs associated with FRBs fits well with the ISM required for DSR to occur. DSR also presents a mechanism through which a repeater can be explained. If separate collections of molecules have DSR triggered at the same time, the intrinsic variation in the DSR time-scales and time delays would give the observation of bursts at different times. The variation is because the time delay is a function of the column density of the inverted population (as well as the wavelength of radiation and the Einstein spontaneous emission coefficient) and variations in this parameter will create a distribution in the time delays and the occurence of FRBs. This process can happen repeatedly since while the population inversion will be quenched by a DSR event, it will eventually be restored via the pumping source responsible for the inversion in the first place. This will drive more FRB pulses, and so on. The flux distribution of such a setup can be matched to FRB 121102.

Observational Constraints