Probing the origins of FRBs using CHIME: High-energy counterpart searches and burst morphology
Bibliographic record
Abstract
Since the initial discovery of a fast radio burst (FRB) at a cosmological distance in 2007, well over 5000 FRBs have been detected. While their extremely short emission timescales of nanoseconds to milliseconds point to a compact object origin, their intrinsic radio luminosities ($\sim10^{36}-10^{44}$ erg s$^{-1}$; assuming isotropic) are at times $\sim$ ten orders of magnitude larger than those of radio pulsars. In this thesis, I investigate the origins of FRBs using the Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB project. I first examine whether FRBs are associated with known high-energy transients, focusing on gamma-ray bursts (GRBs). I develop a pipeline to search for FRB-like signals coincident with GRBs and place some of the first constraints on prompt radio emission from short GRBs. While no significant associations are found, these limits inform models of FRB-GRB associations. Next, I analyze the morphology of repeating FRBs down to microsecond timescales to probe their emission mechanisms and local environments. In contrast to certain previous findings, I find no evidence that the sources studied reside in highly dynamic environments. I also compare the morphology of repeating and non-repeating FRBs at similar high time resolutions. I do not find any significant differences in their local environments, as probed through their scattering timescales. I find for the first time similarities in their sub-burst properties though, possibly suggesting a common emission mechanism. Finally, I describe a calibration strategy for CHIME/FRB Outriggers, a very long baseline interferometry (VLBI) extension of CHIME. I detail a large pulsar campaign conducted with the Very Long Baseline Array to achieve milliarcsecond localizations, proper motions, and parallaxes for $\sim$82 pulsars which will serve as the validation sources for the Outriggers system. I end by discussing the evolution of the FRB field from the beginning of this thesis to the end, and exciting future directions for FRB discoveries.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".