Abdo, A.A.Venter, C.Ackermann, M.Ajello, M.Allafort, A.Fermi LAT2012-02-292012-02-292010Abdo, A.A. et al. 2010. Fermi-LAT discovery of GeV gamma-ray emission from the young supernova remnant Cassiopeia A. Astrophysical journal letters, 710(1):L92-L97. [https://doi.org/10.1088/2041-8205/710/1/L92]2041-82052041-8213 (Online)http://hdl.handle.net/10394/6156https://doi.org/10.1088/2041-8205/710/1/L92We report on the first detection of GeV high-energy gamma-ray emission from a young supernova remnant (SNR) with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope. These observations reveal a source with no discernible spatial extension detected at a significance level of 12.2σ above 500 MeV at a location that is consistent with the position of the remnant of the supernova explosion that occurred around 1680 in the Cassiopeia constellation—Cassiopeia A (Cas A). The gamma-ray flux and spectral shape of the source are consistent with a scenario in which the gamma-ray emission originates from relativistic particles accelerated in the shell of this remnant. The total content of cosmic rays (electrons and protons) accelerated in Cas A can be estimated as W CR sime (1-4) × 1049 erg thanks to the well-known density in the remnant assuming that the observed gamma ray originates in the SNR shell(s). The magnetic field in the radio-emitting plasma can be robustly constrained as B ≥ 0.1 mG, providing new evidence of the magnetic field amplification at the forward shock and the strong field in the shocked ejectaenAcceleration of particlesISM: individual objects (Cassiopeia A)Radiation mechanisms: non-thermal