Commissioning VERITAS and Observations of Extragalactic Sources

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High-energy gamma rays are used to study the most extreme objects in the Universe, such as pulsars, black holes at the center of active galaxies, and gamma-ray bursts. Cosmic gamma rays can also be signatures for new physics beyond the standard models of particle physics and cosmology. Detection of gamma rays is difficult, however, because they are absorbed by the atmosphere. At the low end of the gamma-ray spectrum, the flux of gamma rays is sufficient to detect them with satellites in orbit above the atmosphere. Studies with very-high-energy (VHE) gamma rays, above about 100 GeV, require detectors with thousands of square meters of collection area, which can only be built on the ground. These ground-based devices detect gamma rays indirectly, by detecting the shower of secondary particles produced when a gamma ray interacts in the atmosphere. This research will use the VERITAS imaging Cherenkov telescope array, now being completed in southern Arizona to study gamma rays with energy greater than about 100 GeV. There are a few hundred known gamma-ray sources at energies of 100 MeV to 10 GeV and about thirty VHE gamma-ray sources. The most powerful of these are extragalactic sources, which are believed to have narrow jets of high energy particles beamed for the observed sources in the direction of the Earth. How the jets form and what processes occur in the jets are questions studied by this project. This proposal focuses on learning to use VERITAS to explore the extreme behavior of the two most powerful known classes of gamma-ray source: gamma-ray bursts (GRBs) and active galactic nuclei (AGNs). The details of how GRBs work and the role they play in other high energy phenomena are still being explored. Similarly, measurements of the VHE gamma-ray emission from AGN probe properties of the AGN jet, such as the size of the emission region and strength of the magnetic field. This work has wide-ranging impacts, particularly in the areas of education and technological infrastructure. The public's curiosity about the Universe creates many opportunities to engage their interest and, in the case of students, participation. The researchers will work with their VERITAS collaborators to develop exhibits on high-energy gamma-ray astrophysics for use at science museums and observatory visitors' centers, and to host visiting groups at the VERITAS site.