Colloquium on Apr. 8, 2021

Origins of fast radio bursts and their future applications

Speaker:Tetsuya Hashimoto (NTHU)

Venue:Video Conference

Time:15:00 PM, Thursday, Apr. 8, 2021

Abstract:

Fast radio bursts (FRBs) are a new type of astronomical transients with millisecond time scales, occurring at cosmological distances. Constraining their origins is one of the most important tasks in astronomy. Except for one confirmed case, the origins of the remaining >99% of the current FRB sample are still unknown. To overcome this problem, I performed unique statistical approaches to constrain their origins. Here I show, for the first time, the number density evolutions of non-repeating and repeating FRBs towards the distant Universe (TH+2020c). The number density of non-repeating FRBs is almost constant during the past ~10 Gyr. The nearly-constant density is consistent with a flat trend of cosmic stellar-mass density traced by old stellar populations with ~Gyr time-scales. Our finding strongly narrows down the progenitor candidates of non-repeating FRBs to old objects, e.g., neutron stars. In contrast, the number density of repeating FRBs increases towards the distant Universe in a similar way to the cosmic star formation-rate density or supermassive black hole accretion-rate density. Short-living objects with <~Myr time-scales associated with young-stellar populations (or their remnants, e.g., magnetars) or active galactic nuclei are progenitor candidates of repeating FRBs. Additionally, I will discuss important applications of future FRBs (TH+2020b). I propose a new method to investigate the cosmic reionization history using future FRBs (TH+2021a). In contrast to the cosmic microwave background observations, the new method will allow us to measure the reionization history as it is without any assumption on its functional shape. FRBs are also useful to test Einstein's weak equivalence principle (WEP) in general relativity. Observational uncertainties of FRB dispersion measures place more than one order of magnitude lower upper limits on the WEP violation compared to previous works (TH+2021b). These applications clearly indicate the capability of future FRBs in broad areas in astronomy and physics.

Report PPT:SWIFAR_Tetsuya Hashimoto.pdf