The Spectro-Temporal Relationships of Repeating Fast Radio Bursts
Abstract
Fast radio bursts (FRBs) are short and extremely energetic bursts of radiation detected from galaxies across the universe that occur thousands of times a day. Despite advances in instrumentation, it is difficult to explain the enormous implied energy reservoirs of FRBs, their emission mechanism and the existence of repeating and periodic sources. This thesis explores the spectro-temporal properties of repeating FRBs and details the discovery of several new relationships between them, providing valuable information on the nature of FRBs. By measuring the spectro-temporal properties of a sample of bursts from the repeating source FRB20121102A I show that the magnitude of a burst's time derivative of the frequency (or ``sub-burst slope") is inversely proportional to its duration. This relationship is a key prediction of the triggered relativistic dynamical model (TRDM), a model that assumes FRBs are inherently narrow-band in nature and originate from a cloud of material. I then investigate other FRB sources by analysing bursts from the repeaters FRB20180814A and FRB20180916B, discovering that the same slope-duration relationship describes the bursts from all three sources. Because FRBs are subject to dispersion by free ions along the line of sight, and because the measurement of spectro-temporal properties are dramatically affected by the choice of dispersion measure (DM), measurements of each burst are performed over a range of DMs to estimate uncertainties and validate any relationships found. Finally, I developed a software tool for preparing and measuring properties of FRBs and used it to survey a broad sample of 167 bursts from FRB20121102A. This sample spans 1 to 7 GHz, the entire range of burst frequencies observed for this source. I find relationships between a burst's duration, slope, and frequency consistent with the TRDM, and discover an unexpected relationship between the bandwidth of a burst and its duration. These spectro-temporal relationships can be important tools and suggest a narrow-band emission mechanism for FRBs.