Particle Astrophysics

The VERITAS Cherenkov Telescope Array

Gamma-ray astrophysics probes the cosmos at the highest energies, providing views of the universe relatively undiluted by thermal processes that dominate at lower energies. The discrete physical systems studied include relativistic jets emerging from accretion disks near black holes powering the nuclei of active galaxies, neutron-star powered supernova remants (plerions) and the remnant shock waves from supernova thought to be the origin of galactic cosmic rays. (A few pictures are shown below.) The Iowa State University gamma-ray astrophysics group has primary roles in the development and operation of the VERITAS ground-based array of telescopes.

Cassiopeia AThe smoothed sky map image on the right shows excess counts from Cassiopeia A, a ~340 year old supernova remnant. This was observed by VERITAS for a total of 22 hours in 2007. The color bar indicates the number of excess events, and the white circle indicates the size of the point-spread function. The cross represents the messured position of the TeV gamma-ray source. The radius of the smoothing circular window was 0.115 degrees.

Fermi All-Sky Map Above 1 GeVThe FERMI all sky map on the left clearly shows both galactic objects (in the plane) and extragalactic objects. The LAT (Large Area Telescope) is a high-energy gamma-ray telescope covering the energy range from 20 MeV to more than 300 GeV.

Veritas Gamma-Ray Skymap
At higher energies, ground-based Cherenkov-light imaging telescopes are sensitive to energies greater than about 100 GeV. These are the highest energies at which discrete objects have been observed in nature. Supernova remnants (both plerions and shell-type) and blazars have been discoved at these energies. The imaging technique was pioneered by the VERITAS collaboration, that has constructed an array of these telescopes in southern Arizona.