Gamma-Ray Astrophysics with Upgraded VERITAS

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This application is for funding to support continued McGill participation in the VERITAS gamma-ray astronomy project. VERITAS is one of three major detectors world-wide that study astrophysical gamma rays with energies greater than 100 GeV. 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 astrophysical 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. Over 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. The VERITAS detector has met and exceeded all design specifications but we continue to improve it. In 2009 we moved one of the four telescpes to optimize the array layout and in the summer of 2012 we replaced all photomultipliers in the telescope cameras with newly available high-quantum-efficiency models further increasing our sensitivity. A new trigger has been installed to allow running at lower energy threshold and improved reconstruction and background-rejection techniques have been incorporated into the analysis stream. Based on the output from the previous years we expect a period of high scientific productivity and many exciting new results.