Abdo, A. A.A. A.AbdoAckermann, M.M.AckermannAjello, M.M.AjelloCutini, SaraSaraCutiniGasparrini, DarioDarioGasparriniTosti, G.G.Tosti2020-09-172020-09-172010-02-01https://hdl.handle.net/20.500.13025/2020Science, Volume 327, Issue 5969, pp. 1103- (2010).Recent observations of supernova remnants (SNRs) hint that they accelerate cosmic rays to energies close to ~10<SUP>15</SUP> electron volts. However, the nature of the particles that produce the emission remains ambiguous. We report observations of SNR W44 with the Fermi Large Area Telescope at energies between 2 10<SUP>8</SUP> electron volts and 3 10<SUP>11</SUP> electron volts. The detection of a source with a morphology corresponding to the SNR shell implies that the emission is produced by particles accelerated there. The gamma-ray spectrum is well modeled with emission from protons and nuclei. Its steepening above ~10<SUP>9</SUP> electron volts provides a probe with which to study how particle acceleration responds to environmental effects such as shock propagation in dense clouds and how accelerated particles are released into interstellar space.Article Journal10.1126/science.1182787http://adsabs.harvard.edu/abs/2010Sci...327.1103A2010Sci...327.1103A54dcce0c8580fe1368eeb401