Revisiting SNR Puppis A with Seven Years of Fermi Large Area Telescope Observations

Puppis A is a very famous and extensively studied supernova remnant that shows strong evidence of shock-cloud interaction. We reanalyze its GeV gamma-ray emission using seven years of Pass 8 data recorded by the Fermi Large Area Telescope. The morphology of the gamma-ray emission is more compatible with that of the thermal X-ray and IR emissions than the radio image, which suggests a possible correlation between the gamma-ray-emitting region and dense clouds. The gamma-ray spectrum in the energy range of 1-500 GeV shows a break at 7.92 +/- 1.91 GeV, with photon indices of 1.81 +/- 0.08 below the break and 2.53 +/- 0.12 above the break, which can naturally explain the lack of TeV gamma-ray emission from Puppis A. The multi-wavelength observations favor a hadronic origin for the gamma-ray emission.