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Science 7 August 2009:
Vol. 325. no. 5941, pp. 683 - 684
DOI: 10.1126/science.1177743
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Perspectives

Astronomy:

Cosmic-Ray Acceleration in Supernova Remnants

John C. Raymond

Cosmic rays are ubiquitous in our Galaxy and exhibit a power-law spectrum in their energy distribution up to a "knee" at around 1015 eV, where the power law steepens. It is generally accepted that cosmic rays up to the knee are accelerated by the strong shock waves in supernova remnants, but the efficiency of this acceleration process remains largely unknown. On page 719 of this issue, Helder et al. (1) combine x-ray and optical observations of a supernova remnant to obtain a lower limit to the acceleration efficiency in a fast shock.

Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.

E-mail: raymond{at}cfa.harvard.edu.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)