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Originally published in Science Express on 25 June 2009
Science 7 August 2009:
Vol. 325. no. 5941, pp. 719 - 722
DOI: 10.1126/science.1173383
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Reports

Measuring the Cosmic-Ray Acceleration Efficiency of a Supernova Remnant

E. A. Helder,1,* J. Vink,1 C. G. Bassa,2,3 A. Bamba,4 J. A. M. Bleeker,1,2 S. Funk,5 P. Ghavamian,6 K. J. van der Heyden,7 F. Verbunt,1 R. Yamazaki8

Cosmic rays are the most energetic particles arriving at Earth. Although most of them are thought to be accelerated by supernova remnants, the details of the acceleration process and its efficiency are not well determined. Here we show that the pressure induced by cosmic rays exceeds the thermal pressure behind the northeast shock of the supernova remnant RCW 86, where the x-ray emission is dominated by synchrotron radiation from ultrarelativistic electrons. We determined the cosmic-ray content from the thermal Doppler broadening measured with optical spectroscopy, combined with a proper-motion study in x-rays. The measured postshock proton temperature, in combination with the shock velocity, does not agree with standard shock heating, implying that >50% of the postshock pressure is produced by cosmic rays.

1 Astronomical Institute Utrecht, Utrecht University, Post Office Box 80000, NL-3508 TA Utrecht, Netherlands.
2 SRON Netherlands Institute for Space Research, Sorbonnelaan 2, NL-3584 CA Utrecht, Netherlands.
3 Department of Astrophysics, Radboud University Nijmegen, Post Office Box 9010, Nijmegen, Netherlands.
4 Institute of Space and Astronautical Science–Japan Aerospace Exploration Agency, Department of High Energy Astrophysics 3-1-1, Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan.
5 Kavli Institute for Particle Astrophysics and Cosmology, Stanford, CA 94025, USA.
6 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA.
7 Astronomy Department, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa.
8 Department of Physical Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan.

* To whom correspondence should be addressed. E-mail: e.a.helder{at}uu.nl

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Cosmic-Ray Acceleration in Supernova Remnants.
J. C. Raymond (2009)
Science 325, 683-684
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