Issue |
A&A
Volume 467, Number 1, May III 2007
|
|
---|---|---|
Page(s) | 15 - 20 | |
Section | Astrophysical processes | |
DOI | https://doi.org/10.1051/0004-6361:20066932 | |
Published online | 05 March 2007 |
Confinement and anisotropy of ultrahigh-energy cosmic rays in isotropic plasma wave turbulence*
I. Modification of the Hillas limit due to turbulence geometry
1
Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany e-mail: rsch@tp4.ruhr-uni-bochum.de
2
Department of Physics, University of Montenegro, Podgorica, Montenegro
Received:
14
December
2006
Accepted:
22
February
2007
Context.The mean free path and anisotropy of galactic cosmic rays is calculated in weak plasma wave turbulence that is isotropically distributed with respect to the ordered uniform magnetic field.
Aims.The modifications on the value of the Hillas energy, above which cosmic rays are not confined to the Galaxy, are calculated. The original determination of the Hillas limit has been based on the case of slab turbulence where only parallel propagating plasma waves are allowed.
Methods.We use quasilinear cosmic ray Fokker-Planck coefficients to calculate the mean free path and the anisotropy in isotropic plasma wave turbulence.
Results.In isotropic plasma wave turbulence the Hillas limit is enhanced by about four orders of
magnitude to PeV
resulting from the dominating influence of transit-time damping interactions of cosmic rays with obliquely
propagating magnetosonic waves.
Conclusions.Below the energy Ec the cosmic ray mean free path and the anisotropy exhibit
the well known energy dependence. At energies higher than Ec both transport parameters steepen to a E3-dependence. This implies that cosmic rays even with ultrahigh
energies of several hundreds of EeV can be rapidly pitch-angle scattered by interstellar plasma turbulence, and are thus confined to the Galaxy.
Key words: ISM: cosmic rays / ISM: magnetic fields / plasmas / scattering
© ESO, 2007
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