2009/12/18 by Karlsson, Niklas
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.0912.3807
The galaxy M82 has long been considered a promising target for VHE gamma-ray observations because of the compact starburst region in its core. Theoretical predictions have suggested it should be detectable by ground-based imaging Cherenkov telescopes like VERITAS and that a detection would have implications for the understanding of the origin of cosmic rays. M82 was observed with the VERITAS array during the 2007-2009 observing seasons. With an exposure of 137 hours, VERITAS was able to detect a gamma-ray signal at the 5 sigma level. This marks the discovery of gamma rays not only from M82 but also from the new source class of starburst galaxies. The observed flux from M82 is 3.7± 0.8(stat)± 0.7(syst)x10-13 photons cm-2 s-1 above an energy threshold of 700 GeV, which corresponds to 0.9% of the Crab Nebula flux. The differential energy spectrum is a power law with a photon index Gamma=2.5± 0.6(stat)± 0.2(syst). Both the flux and the photon index is close to recent theoretical predictions. The VERITAS data places a strong correlation between the star-formation activity and the cosmic-ray production in M82.