Volume 453, Number 2, July II 2006
|Page(s)||387 - 395|
|Published online||16 June 2006|
Observational constraints on energetic particle diffusion in young supernovae remnants: amplified magnetic field and maximum energy
IPN Orsay, CNRS/Université Paris-Sud, 91406 Orsay Cedex, France e-mail: email@example.com
2 Centre d'Étude Spatiale des Rayonnements, 9 Av. du Colonel Roche, 31028 Toulouse Cedex 4, France
3 DSM/DAPNIA/SAp, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
4 LPTA, CNRS/Université Montpellier II, 34095 Montpellier Cedex 5, France
Accepted: 23 March 2006
Constraints on the diffusion and acceleration parameters in five young supernova remnants (SNRs) are derived from the observed thickness of their X-ray rims, as limited by the synchrotron losses of the highest energy electrons, assuming uniform and isotropic turbulence. From a joint study of the electrons diffusion and advection in the downstream medium of the shock, it is shown that the magnetic field must be amplified up to values between 250 and 500 μG in the case of Cas A, Kepler, and Tycho, or G in the case of SN 1006 and G347.3-0.5. The diffusion coefficient at the highest electron energy can also be derived from the data, by relating the X-ray energy cutoff to the acceleration timescale. Values typically between 1 and 10 times the Bohm diffusion coefficient are found to be required. We also find interesting constraints on the energy dependence of the diffusion coefficient, by requiring that the diffusion coefficient at the maximum proton energy be not smaller than the Bohm value in the amplified field. This favours diffusion regime between the Kraichnan and the Bohm regime, and rejects turbulence spectrum indices larger than . Finally, the maximum energy of the accelerated particles is found to lay between 1013 and eV for electrons, and around eV at most for nuclei (or ∼2.5 times less if a Bohm diffusion regime is assumed), roughly independently of the compression ratio assumed at the shock. Even by taking advantage of the uncertainties on the measured parameters, it appears very difficult for the considered SNRs in their current stage of evolution to produce protons up to the knee of the cosmic-ray spectrum, at eV, and essentially impossible to accelerate Fe nuclei up to either the ankle at eV or the second knee at eV.
Key words: acceleration of particles / magnetic fields / cosmic rays / ISM: supernova remnants
© ESO, 2006
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