Observations of Very High Energy Gamma-Ray Emission from Supernova Remnants with VERITAS

The nature and source of cosmic rays has been at the core of particle astrophysics since their discovery almost a century ago. The cosmic ray spectrum is best described by a broken power law, and can be better understood as three distinct parts. Theory holds that cosmic rays up to ∼1015 eV – those below the “knee” or steepening in the spectrum – are produced in the shocks of supernova remnants. Direct detection of cosmic rays produced in supernova remnant shocks is impossible, however, as cosmic rays below ∼1018 eV are deflected by the Galactic magnetic field and cannot be traced back to their origins. If high energy hadrons are produced within the immediate environment of a supernova remnant, collisions will occur within the surrounding medium. As a result, pion production and subsequent decay will give rise to very high energy gamma rays (E\u3e100 GeV). Since these gamma rays will not interact with any magnetic field, they can be traced back to their point of origin. Thus, Atmospheric Cherenkov Detectors like VERITAS, which have the capability to detect very high energy gamma rays via their interaction with our atmosphere, provide us the means of directly testing the theory of the origin of cosmic rays in supernova remnants. Observations of 13 supernovae made with the VERITAS instrument are presented herein, including 5 individually targeted remnants and 8 remnants within the VERITAS Cygnus region Sky Survey. The observations provide detections of two known VHE remnants (Cassiopeia A and the Crab Nebula), and meaningful flux limits on the remainder. Comparison of these results to both hadronic- and leptonic-origin emission models is carried out