Understanding Very High Energy Cosmic Rays with VERITAS
The origin of very high energy (VHE) cosmic rays is one of the oldest and deepest puzzles of astrophysics. Understanding particle production and acceleration in astrophysical sources, and the mechanisms of propagation of cosmic rays through the interstellar medium is paramount to solving this fundamental problem. Cosmic rays produced in nearby accelerators can be observed directly through measurements of the spectra of cosmic ray electrons, as well as heavy elements, including iron. On the other hand, one of the most powerful ways of studying cosmic rays from singular distant accelerators is the observation of gamma rays that are produced in their interactions with the interstellar medium. Such studies are then most productive focusing on dense energetic regions of space – supernova remnants and starburst cores of nearby galaxies. Imaging atmospheric Cherenkov telescopes (IACTs), such as VERITAS, that detect atmospheric particle showers initiated by VHE cosmic and gamma rays, are uniquely suited for both modes of study. In this talk, we attempt to find clues about the origin of cosmic rays by looking at the VHE gamma ray emission from one of the weakest known extragalactic sources, the starburst galaxy M82, observed with VERITAS and the Fermi Gamma-ray space telescope. We also report on VERITAS studies of the cosmic-ray electron and iron spectra.