Cosmic Rays

Nearly a century after their 1912 discovery by Victor Hess the origin of these energetic particle streaming to us from space remains controversial. Where in the universe is there an accelerator far more powerful than anything we can build on Earth? Supernova remnants, young stars, microquasars and even quasars have been suggested. Thanks to new observational tools progress is Several people at the High-Energy Astrophysics division are working on different aspects of the cosmic ray (CR) acceleration problem. In order to work towards solving the GCR acceleration problem, we are in the process of carrying out multifrequency observations of turbulent acceleration sites such as powerful associations of young (OB) stars and 'superbubbles'. We have an active observational program including radio, mm, sub-mm, X-ray, and TeV gamma-rays, and collaborate widely with colleagues in the US, Europe and Japan. The Supernova Remnant group is investigating diffusive shock acceleration in these remnants. process). Supernova remnants (SNRs) have enough energy to power the cosmic rays and so have long been considered a likely primary source of at least the less energetic cosmic rays (ie those below "the knee" of the spectrum, with energies less than 1015 electron volts). Only recently though have observational evidence has emerged supporting the acceleration of particles to cosmic ray energies in SNRs by "First-order Fermi shock acceleration" (also called diffusive shock acceleration), as particles gain energy by scattering back and forth across the shock.