Localized Fast Radio Bursts Using DSA-110

Citation

Chen, Ge (2024) Localized Fast Radio Bursts Using DSA-110. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/xchy-q017. https://resolver.caltech.edu/CaltechTHESIS:12192023-224904219

Abstract

Fast Radio Bursts (FRBs) are µs- to ms- scale, energetic (10^40~46 erg s^-1) bursts detected in the radio frequency (110 MHz to 8 GHz). They primarily originate from extragalactic sources and are likely to originate from compact object sources. The exact nature of the sources and the emission mechanisms remain inconclusive.

The first FRB was not confirmed until 2007. By early 2023, over 600 FRBs have been reported, and about 40 FRBs have been associated with an individual host galaxy. The rapid growth in sample size has helped to greatly narrow down the number of source models. Neutron stars, especially magnetars, have been the most popular source candidate, although other possibilities still remain.

In this thesis, we explore a few observational methods to study the potential FRB source and host environments. In Chapter 2, we demonstrated a method to constrain the energy ratio emitted from the FRB's multiwavelength transient counterparts as compared to the FRB energy themselves. We used the existing multiwavelength transient blind survey database and the current FRB population fluence distribution to produce tighter constraints than most targeted surveys. In Chapter 3, we investigated whether or not the persistent radio source associated with FRB 121102 could be an AGN using the VLA monitoring data and a new Keck optical spectrum. We constrained the emission source radius to be 10^17~18 cm based on the low level of variability in the VLA radio flux measurements presented in this work as compared to the Galactic scintillation theory and other published results by VLBI. We estimated the mass of the potential black hole to be ≾10^4~5 M☉ based on the Hα line width in the Keck spectrum. We concluded that the source is unlikely an AGN based on the size, mass, and radio luminosity, and that the persistent radio source could be explained by an isolated neutron star with a pulsar wind nebula. In Chapter 4, we showed the burst morphology of a sample of 21 FRBs detected by DSA-110 during part of the commissioning period in 2022, including 16 localized FRBs with optical spectra. We explored the potential correlation between burst morphology and host properties. We found a strong correlation between the host Hα luminosity and FRB burst energy that is likely a result of observational selection effects. We measured the scintillation timescales and found most of them close to the predicted Galactic scintillation timescales. In Chapter 5, we summarize the thesis and very briefly discussed potential extensions of the above methods for the study of FRB sources.

Thesis Files