Particle Astrophysics with the VERITAS Detector

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This application is for funding to support continued McGill participation in the VERITAS gamma-ray astrophysics project. VERITAS (Very Energetic Radiation Imaging Telescope Array System) is one of three major detectors world-wide that study astrophysical gamma rays with energies greater than 100 GeV, using the Imaging Atmospheric Cherenkov Technique. It consists of an array of four large telescopes designed to detect the ultraviolet and blue Cherenkov light emitted by energetic electrons and positrons produced when high-energy gamma rays interact in the upper atmosphere. Such gamma rays are produced in extreme environments such as supernova remnants and active galactic nuclei. There may also be gamma rays which come from more exotic origins such as annihilation of dark-matter particles in the cores of galaxies or from evaporation of primordial black holes. As such, they could provide information about particle physics at energies beyond what can be probed at Earth-bound accelerators. The VERITAS array, located in southern Arizona, was completed in 2007 and began four-telescope observations in September of that year. So far we have detected over 40 sources of astrophysical gamma rays, in eight classes. Approximately half of these are new discoveries; the remainder are confirmations. We have participated in multi-wavelength campaigns with data from X-ray, optical and radio telescopes, as well as the Fermi Gamma-ray Space Telescope which covers the gamma-ray energy range just below that where VERITAS is sensitive. A new ground-based all-sky detector, HAWC, operates at energies slightly higher than those in the VERITAS range and we have started a program of coordinated observations with them. Follow-ups on interesting hints from the IceCube neutrino observatory and the Pierre Auger ultra-high-energy cosmic-ray observatory are part of our program, with similar activities connected to the LIGO gravitational wave observatory about to begin.