Cosmic ray propagation in a fractal galactic medium
Keywords:
cosmic ray, diffusion, fractal, magnetic field
Abstract
Simple cosmic ray diffusion in magnetic fields is often discussed in terms of a characteristic scattering mean free path or equivalent diffusion coefficient. This assumes very simple properties of the structure of astrophysical magnetic fields. A better approximation is to assume that the magnetic structure has fractal properties and there is then the possibility of including very short and very long interaction lengths when modelling the propagation. Results of modelling such propagation in a fractal medium are discussed. Values of the propagation parameter (α) less than 2 were obtained and confirm the plausibility of the hypothesis that supernova are the origin of galactic cosmic rays in the energy range below the knee in the spectrum.References
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2. Axford WI. The modulation of galactic cosmic rays in interplanetary medium. Planet Space Sci. 1965;13:115–130. doi:10.1016/0032-0633(65)90181-9
3. Berezhko EG, Elshin VK, Ksenfontov LT. [Cosmic ray acceleration in supernova remnants.] Zh Eksp Teor Fiz. 1996;109:3 [IETP (English translation);109:1]. Russian.
4. Elmegreen BG, Kim S, Staveley-Smith L. A fractal analysis of the HI emission from the Large Magellanic Cloud. Astrophys J. 2001;548:749. doi:10.1086/319021
5. Lagutin AA, Makrov VV, Tyumentsev AG. Anomalous diffusion of the cosmic rays: Steady state solution. Paper presented at: ICRC 2001. Proceedings of the 27th International Cosmic Ray Conference; 2001 Aug 7–15; Hamburg, Germany. Berlin: Copernicus GmbH; 2001. p. 1889.
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7. Erlykin AD, Lagutin AA, Wolfendale AW. Properties of the interstellar medium and the propagation of cosmic rays in the galaxy. Astropart Phys. 2003;19:351–362. doi:10.1016/S0927-6505(02)00216-5
8. Bouchaud JP, Georges A. Anomalous diffusion in disordered media: Statistical mechanics, models and physical applications. Phys Rep. 1990;195:127. doi:10.1016/0370-1573(90)90099-N
9. Buesching OC, Jager DE, Potgieter MS, Venter C. A cosmic ray positron anisotropy due to two middle-aged, nearby pulsars. Astrophys J. 2008;678:L39–L42. doi:10.1086/588465
10. Erlykin AD, Wolfendale AW. The origin of cosmic rays. Europhysics News. 2001;32:1–10. doi:10.1051/epn:2001617
11. Erlykin AD, Wolfendale AW. A single source of cosmic rays in the range 1015 _ 1016 eV. J Phys G: Nucl Part Phys. 1997;23:976–989. doi:10.1088/0954-3899/23/8/012
Published
2011-01-24
Section
Research Letters