Date of Award
2025
Document Type
Open Access Dissertation
Degree Name
Doctor of Philosophy in Physics (PhD)
Administrative Home Department
Department of Physics
Advisor 1
Petra H. Huentemeyer
Committee Member 1
Brian E. Fick
Committee Member 2
Elena Giusarma
Committee Member 3
Miguel Mostafa
Abstract
Since the discovery of cosmic rays, i.e., protons, electrons, and atomic nuclei originating from space, and the birth of astroparticle physics, scientists have searched for the most energetic particle accelerators in our galaxy. PeVatrons are astrophysical objects capable of accelerating cosmic rays to peta-electronvolt energies. Studying the nature of PeVatrons allows scientists to study particle physics at energies three orders of magnitude higher than those achievable with Earth-based particle accelerators. While PeVatrons can accelerate both electrons and protons, it is thought that searching for hadronic PeVatrons is more fruitful, given the limitations of accelerating electrons to such high energies. In this dissertation, I will probe the nature of ultra-high-energy gamma-ray emission (UHE; >10s TeV) from hadronic PeVatrons using the High-Altitude Water Cherenkov (HAWC) observatory and the Southern Wide-field Gamma-ray Observatory (SWGO).
The HAWC observatory is located in Puebla, Mexico. It is a wide-field-of-view survey instrument sensitive to gamma rays in the 300 GeV to 100s TeV range and utilizes single-layer water Cherenkov detectors (WCDs). For UHE gamma-ray emission to be produced by protons from hadronic PeVatrons, some type of matter, like molecular clouds, must be nearby. This has made molecular clouds a promising tracer for hadronic PeVatrons. This dissertation details a study of the believed PeVatron supernova remnant (SNR) G106.3+2.7. The molecular cloud template fit performed on UHE data from HAWC reveals that the SNR is fully capable of producing a population of >560 TeV protons that have an energy budget of 7.62x1044 erg. In an attempt to probe more galactic hadronic PeVatrons, I also present HAWC's second catalog of UHE gamma-ray sources: the 2eHC catalog. In the 2eHC catalog, a total of 27 sources are detected above 56 TeV, where 19 sources have a nearby SNR, 18 have a nearby pulsar wind nebula, 10 have a nearby binary system, and 1 has a nearby star-forming region.
There is currently no wide-field-of-view instrument in the southern hemisphere, leaving a large fraction of our southern sky unobserved in the 100s TeV range. SWGO is a next-generation, ground-based, gamma-ray observatory that will be built in Chile. With a sensitivity up to 1 PeV, SWGO will be ideal for surveying the southern gamma-ray sky for hadronic PeVatrons. SWGO evaluated a phase space encompassing many tank variations and array layouts using background rejection capabilities to determine the optimal WCD for SWGO's science objectives. This dissertation details the implementation of background rejection algorithms, adopted from HAWC, into SWGO's reconstruction chain. The results presented herein show that the double-layered WCDs have superior background rejection capability compared to the single-layered detectors. The final part of this dissertation details a successful prototyping effort to build a double-layered WCD at the HAWC site. These prototyping efforts are crucial for validating the technical feasibility of the detector technology.
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Recommended Citation
Turner, Rhiannon M., "STUDYING THE HADRONIC NATURE OF ULTRA-HIGH-ENERGY GAMMA-RAY EMISSION USING WIDE-FIELD-OF-VIEW INSTRUMENTS", Open Access Dissertation, Michigan Technological University, 2025.