A stochastic approach to Galactic proton propagation: influence of the spiral arm structure
Abstract
A newly developed numerical code solving Fokker-Planck type transport equations in space, momentum (or energy) and time by means of stochastic differential equations (SDEs) is applied to the Galactic propagation of cosmic ray protons, where the paths of pseudo-particles originating in spiral arms and in the inter-arm region are traced back to a distribution of discrete point sources. The transport equation includes spatial diffusion and catastrophic energy losses. Although the code allows for a fully anisotropic diffusion tensor, we validate the code as a first step by obtaining results being consistent with previous ones obtained with finite-difference methods and scalar diffusion, revealing lower spectra with less variations in the inter-arm region. In a second step, we concentrate on a diffusion coefficient taking into account the spiral arm structure. Such a variable diffusion coefficient is of importance e.g. for the time-variation of the cosmic ray flux at Earth related to spiral arm crossings. We find that a diffusion coefficient reflecting the spiral arm structure leads to a considerably enhanced flux ratio between the in-arm and inter-arm regions.
- Publication:
-
40th COSPAR Scientific Assembly
- Pub Date:
- 2014
- Bibcode:
- 2014cosp...40E1577K