Predoctoral Projects, 2014

Project Title: Very High Energy Gamma-Ray Astronomy with VERITAS

Project Advisor: Dr. Wystan Benbow

Background: VERITAS (Very Energetic Radiation Imaging Telescope Array System) is a stereoscopic array of four atmospheric-Cherenkov telescopes that are sensitive to very high energy (VHE; E> 100 GeV) gamma rays. Located at the F.L.Whipple Observatory in southern Arizona, USA, the array began operation in 2007, and is currently the most sensitive VHE observatory in the world. The VERITAS Collaboration, which consists of ~100 scientists from institutions in the U.S.A., Canada, Germany, and Ireland, is carrying out observations that cover a broad range of science topics. VERITAS seeks to both identify new sources of VHE gamma rays, and to perform in-depth studies (e.g. spectral, temporal and morphological measurements) of the known VHE sources to better understand their underlying fundamental processes. The results of these studies often have broad implications beyond the physics of the objects. Other topics addressed include fundamental physics (e.g. the energy dependence of! the speed of light), cosmology, the origin of cosmic rays, and the search for dark matter. VERITAS is a major contributor to the rapidly emerging field of gamma-ray astrophysics, where in the past ~10 years the number of known astrophysical VHE sources has grown from ~10 to ~150.

Scientific Questions: What is the population of extragalactic very high energy gamma-ray emitters? What are the underlying non-thermal mechanisms behind these powerful particle accelerators? How do supermassive black holes accrete matter and produce powerful jets? How do AGN jets accelerate particles and are they sources of ultra-high energy cosmic rays? What is the origin of, and the timescales of, the extreme variability observed in VHE gamma-ray emitting blazars? How much electromagnetic radiation did the Universe produce since recombination? What is the relation between star formation and the origin of cosmic rays?

Scientific Methodology: The SAO VERITAS group focuses on VHE observations of extragalactic objects including: active galactic nuclei (primarily blazars), radio galaxies, starburst galaxies, gamma-ray bursts and dark-matter dominated structures (e.g. galaxy clusters and dwarf galaxies). Since VHE gamma-ray sources emit radiation over ~20 orders of magnitude in energy, these studies often involve collaboration with experiments at lower energies (e.g., the Fermi Gamma-ray Space Telescope, several X-ray satellites (Chandra, Swift, XMM, Suzaku), and numerous optical and radio facilities). The multi-wavelength data are used to search for temporal flux correlations and variability time scales, and to generate spectral energy distributions enabling the non-thermal processes behind the observed emission to be modeled. In addition the VHE gamma-ray spectra of distant blazars are used to generate significant constraints on the density of the extragalactic background light in the optical and infrared bands. Members of the SAO group spend considerable time at the VERITAS site observing, maintaining the optics of the telescopes, and assisting with the continual upgrades to the various subsystems of the array.

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    Clay Fellow Warren Brown