Gamma-Ray Emission from the Shell of Supernova Remnant W44 Revealed by the Fermi LAT

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Science  26 Feb 2010:
Vol. 327, Issue 5969, pp. 1103-1106
DOI: 10.1126/science.1182787

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Recent 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 space.

  • * National Research Council Research Associate, National Academy of Sciences, Washington, DC 20001, USA.

  • Royal Swedish Academy of Sciences Research Fellow.

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