EDP Sciences
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Volume 419, Number 3, June I 2004
Page(s) L27 - L30
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040130

A&A 419, L27-L30 (2004)
DOI: 10.1051/0004-6361:20040130


Direct evidence of efficient cosmic ray acceleration and magnetic field amplification in Cassiopeia A

E. G. Berezhko1 and H. J. Völk2

1  Institute of Cosmophysical Research and Aeronomy, 31 Lenin Av., 677891 Yakutsk, Russia
    e-mail: berezhko@ikfia.ysn.ru
2  Max-Planck-Institut für Kernphysik, Postfach 103980, 69029 Heidelberg, Germany

(Received 12 February 2004 / Accepted 4 April 2004 )

It is shown that the nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) describes the shell-type nonthermal X-ray morphology of Cas A, obtained in Chandra observations, in a satisfactory way. The set of empirical parameters, like distance, source size and total energy release, is the same which reproduces the dynamical properties of the SNR and the spectral characteristics of the emission produced by CRs. The extremely small spatial scales in the observed morphological structures at hard X-ray energies are due to a large effective magnetic field $B_{\rm d}\sim 500$  $\mu$G in the interior which is at the same time not only required but also sufficient to achieve the excellent agreement between the spatially integrated radio and X-ray synchrotron spectra and their calculated form. The only reasonably thinkable condition for the production of such a large effective field strength is a very efficiently accelerated nuclear CR component. Therefore the Chandra data confirm first of all the inference that Cas A indeed accelerates nuclear CRs with the high efficiency required for Cas A to be considered as a member of the main class of Galactic CR sources and, secondly, that the nonlinear kinetic theory of CR acceleration in SNRs is a reliable method to determine the magnetic field value in SNRs.

Key words: cosmic rays -- shock acceleration -- nonthermal emission -- supernova remnants -- individual: Cas A

Offprint request: H. J. Völk, Heinrich.Voelk@mpi-hd.mpg.de

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