We report on observations of the supernova remnant Cassiopeia A in the energy range from 100 MeV to 100 GeV using 44 months of observations from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope .
We perform a detailed spectral analysis of this source and report on a low-energy break in the spectrum at 1.72 ^ { +1.35 } _ { -0.89 } GeV .
By comparing the results with models for the \gamma -ray emission , we find that hadronic emission is preferred for the GeV energy range .