The Astrophysical Journal, Volume 714, pp. 163-169 (2010)
Abstract
We report on observations of very high energy γ rays from the shell-type supernova remnant (SNR) Cassiopeia A with the Very Energetic Radiation Imaging Telescope Array System stereoscopic array of four imaging atmospheric Cherenkov telescopes in Arizona. The total exposure time for these observations is 22 hr, accumulated between September and November of 2007. The γ-ray source associated with the SNR Cassiopeia A was detected above 200 GeV with a statistical significance of 8.3σ. The estimated integral flux for this γ-ray source is about 3% of the Crab-Nebula flux. The photon spectrum is compatible with a power law dN/dE 
E –Γ with an index Γ = 2.61 ± 0.24stat ± 0.2sys. The data are consistent with a point-like source. We provide a detailed description of the analysis results and discuss physical mechanisms that may be responsible for the observed γ-ray emission.
