2020-12-15 12:20 Abstract
Title: Origins of fast radio bursts and their future applications
Speaker: Dr. Tetsuya Hashimoto (NTHU)
Date: December 15 at 12:20
Location: R521, General Building II
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. 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. I, also for the first time, constrained the progenitors of FRBs statistically, bringing a breakthrough in understanding the origins of FRBs (TH+2020a,c). Additionally, I will discuss important applications of future FRBs. I discovered the non-repeating FRBs to be the new standard candle over the traditional type Ia supernovae (TH+2019a). Future FRBs to be detected with the Square Kilometre Array (TH+2020b) will allow us to address the time variability of the dark energy for the first time. I also propose a new method to investigate the cosmic reionization history using future FRBs (TH+2020d). 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. These applications clearly indicate the capability of future FRBs in broad areas in astronomy.