Light at the Highest Energies

Wed., Feb. 25, 2015 3:30 p.m. - Wed., Feb. 25, 2015 4:30 p.m.

Location: CL 410

Abstract: Humanity's view of the Universe evolved considerably over the course of the last 100 years, as larger telescopes allowed one to see farther out into space and further back in time. At the same time, previously unexplored parts of the electro magnetic spectrum, on both sides of the visible portion, were opened up, revealing new objects and processes to study and explain. One of the last parts of the spectrum to be explored was that where X-rays and gamma rays are found. It was necessary to wait for the dawn of the space age so that one could send telescopes above the atmosphere. However the limited size of such instruments, coupled with the rapidly falling energy spectra of astrophysical sources, effectively placed an upper limit of ~100 GeV on this range. However, following a long struggle in which scientists learned how to use the atmosphere itself as part of the detector, the goal of ground-based gamma-ray astronomy at energies well beyond this limit has been achieved and a new window on the sky has been opened. Science is now being done using photons with energies well in excess of any that can be produced on Earth. In this talk I will describe the history of how TeV gamma-ray astronomy came into being. I will discuss the scientific motivations, which include searches for dark matter, tests of Lorentz invariance, and a variety of topics in high-energy astrophysics. After reviewing results from the present generation of instruments I will finish with a brief overview of future projects now in development.

Speaker: Prof. David Hanna, Department of Physics, McGill University

David Hanna graduated from McGill University with a BSc in Physics in 1975. He then went to Harvard University and worked in Carlo Rubbia's group using the CERN intersecting storage rings (ISR), the world's first proton-proton collider. After earning his PhD in 1980 he worked as a postdoc at CERN until joining the National Research Council in 1983. In 1985 he returned to McGill as an assistant professor. While at NRC, Hanna worked on constructing the OPAL e+e- detector at CERN but he switched to the ZEUS ep scattering experiment at DESY (Hamburg) shortly after moving to McGill. In the mid 1990's he changed his focus from accelerator-based particle physics to very-high-energy gamma-ray astronomy and was a founding member of the STACEE collaboration which built a gamma-ray 'telescope' using the heliostat mirrors of a solar power installation in New Mexico. More recently he has been a member of the VERITAS collaboration which has constructed the world's most sensitive detector for astrophysical gamma rays, in southern Arizona.