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Dr. Fereshteh Rajabi - Waterloo University


Date: July 19, 2022

Time: 9:00 am

Location: BSB 106

Guest: Dr. Fereshteh Rajabi
Perimeter Institute for Theoretical Physics
Waterloo University

Title: Dicke's superradiance in Astrophysics

Burst phenomena covering a wide range of timescales are ubiquitous in astrophysics (e.g., from less than a millisecond for Fast Radio Bursts to several years for some flares in maser sources). Understanding their origin and underlying physical processes is an important goal of contemporary astrophysics. To this end, we have recently applied Dicke’s superradiance, a coherent quantum mechanical radiation mechanism, to the physics of the interstellar medium (ISM) to explain some of these burst phenomena. In this presentation, I will first focus on so-called maser flares and show how under certain conditions a region initially hosting a maser can transition to a superradiance regime. When superradiance sets in, individual molecules (or atoms) do not emit independently but do so as a group and radiate through powerful bursts with a peak intensity proportional to the square of the number of molecules contained in the radiating gas. Although it was first discussed by R. H. Dicke in 1954 and has been studied in the laboratory for several decades, superradiance remained unnoticed by astronomers until recently. I will thus present observational evidence for superradiance in the ISM and describe our models developed to explain corresponding radiation flares seen in spectral lines commonly used for maser studies. Finally, investigations of superradiance within the context of fast radio bursts (FRBs) have led us to the development of a more general dynamical and relativistic model. Not only can this model reproduce some of the previously observed characteristics of repeating FRBs (e.g., the sad trombone effect) but, more importantly, it also predicts the existence of a relationship between the frequency drift in a single sub-burst and its temporal duration (the “sub-burst slope law”). I will present the observational evidence that verifies this law for several sources associated with different types of host galaxies at various redshifts.
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