Astrophysics with Very High Energy Gamma Rays

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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. Studies with very-high-energy gamma rays, above about 100 gigaelectron volt (GeV), require ground-based detectors with thousands of square meters of collection area. This research will use the VERITAS imaging Cherenkov telescope array in southern Arizona to study gamma-rays with energy greater than about 100 GeV. The sensitivity of VERITAS is more than an order of magnitude better than previous generation instruments operating in this energy range and has just been improved further by a substantial upgrade. With this award the University of California - Santa Cruz group will use VERITAS to explore the extreme behavior of the two most powerful known classes of gamma-ray source: gamma-ray bursts and active galactic nuclei. The detail mechanisms of gamma-ray bursts and the role they play in other high-energy phenomena are still being explored. Learning whether they are capable of creating very-high-energy gamma-rays will constrain gamma-ray burst models and properties of the burst environment. Similarly, measurements of the very-high-energy gamma-ray emission from active galactic nuclei probe properties of the jets, providing crucial information about the particles being accelerated and how the acceleration works. Data from across the electromagnetic spectrum will be gathered and used to assemble the most complete possible picture of very high-energy gamma-ray behavior. These data will also be used to study gamma-ray absorption by collisions with the extragalactic background light, a process that tests cosmological models of star formation and galaxy evolution.Broader Impact: Graduate and undergraduate students play an important part in this research effort. Research experiences will also be made available to aspiring science teachers in the Cal Teach program and in-service teachers through a new Lick Observatory Teachers Institute. The researchers interact with the California State University to foster undergraduate interest in research and graduate education. There is an important interplay between the VERITAS data and data from other wavelengths, particularly X-ray and lower energy gamma-ray data from satellite missions such as Swift and Fermi. More can be learned from both types of data used together than from either alone.