The discoveries made by ground-based gamma-ray observatories over the past decade have revolutionized the field of high energy particle astrophysics. The catalog of sources emitting high energy (more than 100 GeV) gamma rays now consists of ~100 objects, and new sources, and source classes, continue to be found. Supernova remnants, pulsars and pulsar wind nebulae, blazars, radio galaxies, starburst galaxies and stellar-mass binary systems have all been shown to emit very high energy gamma-radiation, along with numerous sources whose identification is still unclear. As well as probing sites of extreme particle acceleration in the Universe with unprecedented spectral, temporal and spatial resolution, gamma-ray observations may allow us to indirectly determine the nature of the dark matter that makes up a significant fraction of the universe.
This award will provide operational support for the group's ongoing research using VERITAS, an array of four large imaging atmospheric Cherenkov telescopes sited in Arizona. They will use gamma-ray observations to study sites of particle acceleration in the Universe, focusing on supernova remnants and gamma-ray binary systems, with both deep observations of known sources, and discovery observations of new candidates. They will search for > 100 GeV gamma-ray emission from regions of excess astrophysical neutrinos (identified by IceCube), or ultra-high energy cosmic rays (identified with Auger).
The Delaware group will continue its education and public outreach activities through mentoring of students at the high school and undergraduate level. Members of the group will also give public presentations to local amateur astronomers, and other interested groups, as well as supporting the overall VERITAS outreach program by providing website materials and conducting on-site tours.
VERITAS is an array of four imaging atmospheric Cherenkov telesopes located at the Fred Lawrence Whipple Observatory near Tucson, Arizona. The telescopes are used to observed gamma-rays (photons of the highest energy) from astrophysical sources. VERITAS covers the range from 100 GeV to 30 TeV, complementing space-based observatories such as NASA's Fermi Gamma-ray Space Telescope, and survey instruments like HAWC. Construction of VERITAS was completed in 2007, and the instruments are operated by a collaboration of 100 scientists. This award provided support for the research conducted with VERITAS by the gamma-ray astronomy group in the Department of Physics and Astronomy at the University of Delaware. Our focus has been on observations of supernova remnants and gamma-ray binary systems, and on the overlap with other astroparticle physics observatories such as the IceCube Neutrino Observatory. The study of Tycho's supernova remnant in TeV gamma rays was one highlight of this project, described in a 2014 PhD thesis. This result provides some evidence for the theory that cosmic rays are accelerated within the expanding shock waves of supernova explosions. We have also helped to identify a new member of the class of TeV gamma-ray binary systems, containing a black hole or neutron star in orbit with a massive stellar companion. Only a handful of these objects have been discovered, and the mechanisms by which they accelerate particles and produce gamma-rays are still not well understood. The Delaware group has co-hosted an annual "Fermi summer school" at the University conference center in Lewes, Delaware, in collaboration with members of NASA's Fermi Gamma-ray Space Telescope team. This has provided training and instruction for typically 30 graduate students and post-doctoral researchers each year. Numerous public talks have provided a forum to present our results to the wider public audience.
