A Survey of the Highest-Energy Astrophysical Sources with the HAWC Observatory
Open Access
- Author:
- Malone, Kelly Anne
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 04, 2018
- Committee Members:
- Miguel Mostafa, Dissertation Advisor/Co-Advisor
Miguel Mostafa, Committee Chair/Co-Chair
Stephane Coutu, Committee Member
Douglas Cowen, Committee Member
Peter Istvan Meszaros, Outside Member - Keywords:
- gamma rays
gamma ray
cosmic-ray sources
particle astrophysics
HAWC - Abstract:
- Since Galactic cosmic rays have been observed up to at least PeV energies, Galactic sources capable of accelerating particles to these energies should exist. These sources are called “PeVatrons”. Characteristic gamma-ray signatures of a PeVatron include a hadronic, hard spectrum that extends past 100 TeV without any signs of a cutoff or attenuation. Until recently, no gamma-ray experiment had the sensitivity to make detections at 100 TeV. This dissertation outlines the first extremely high energy catalogs of the High Altitude Water Cherenkov (HAWC) Observatory. Two such catalogs are created: one of sources emitting above 56 TeV, and one of sources emitting above 100 TeV. HAWC consists of an array of 300 Water Cherenkov Detectors (WCDs) located at 4100 meters above sea level, near the peak of the extinct volcano Sierra Negra in the state of Puebla, Mexico. Each WCD is equipped with four photomultiplier tubes (PMTs) in a tank of water and can detect the Cherenkov light emitted when the charged particles from the extensive air shower created when a gamma-ray hits the Earth’s atmosphere make it to ground level. Due to the high duty cycle (nearly 24/7) and large field-of-view (∼2 sr) of the experiment, it is well-poised to perform all-sky surveys. These catalogs are created using a new energy estimation technique that uses the PMT charge 40 meters from the air shower axis. This technique has been validated on the Crab Nebula and then applied to the Galactic plane. There are six sources in the Galactic plane that emit above 56 TeV. Three of them continue to emit past 100 TeV. These are the highest energy gamma-ray sources ever detected. While the gamma ray emission in some of these sources is likely purely leptonic in origin, for some of them a hadronic component cannot be ruled out and they may be considered PeVatron candidates.