The 2009 Fermi Symposium

VERITAS Detection of Starburst Galaxy M 82

Niklas Karlsson, Adler Planetarium

Abstract:

The Milky Way galaxy is a well-established source of gamma rays, with contributions from both discrete astrophysical sources and a diffusion component produced by the interactions of cosmic rays with interstellar matter. These cosmic rays are believed to originate in winds of massive stars and supernova remnant shocks. Such sites are not unique to the Galaxy and other galaxies are expected to produce gamma rays in a similar manner. They are unlikely to be detectable unless the flux of cosmic rays therein is significantly higher than in the Milky Way Galaxy. Starburst galaxies have highly enhanced star-formation rates, possibly induced by the interaction or even merger with another galaxy. The enhanced star-formation rate implies a high supernova rate as well as a dense interstellar medium. Thus starbursts provide excellent laboratories for studying the origin of cosmic rays outside of the Milky Way Galaxy.

During the past two years, VERITAS dedicated about 10% of its total observing time in search for VHE gamma rays from the starburst galaxy M 82. With 137 hours of quality-selected live time, VERITAS was able to detect >700 GeV gamma rays from M 82 at the 5 sigma level. This detection strongly supports the connection between cosmic-ray acceleration and star-formation activity and that the dominant accelerators are supernova remnants and massive-star winds. Here we report on the details of the detection and some of the model implications.