Abdo, A.A.Venter, C.Ackermann, M.Ajello, M.Baldini, L.Fermi LAT2012-02-292012-02-292010Abdo, A.A. et al. 2010. Gamma-Ray emission from the shell of supernova remnant W44 revealed by the Fermi LAT. Science, 327(5969):1103-1106. [https://doi.org/10.1126/science.1182787]0036-80751095-9203 (online)http://hdl.handle.net/10394/6150http://science.sciencemag.org/content/327/5969/1103https://doi.org/10.1126/science.1182787Recent observations of supernova remnants (SNRs) hint that they accelerate cosmic rays to energies close to ~1015 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 × 108 electron volts and 3 ×1011 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 ~109 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 spaceen