Regimes of cosmic-ray diffusion in Galactic turbulence

Abstract

Cosmic-ray transport in astrophysical environments is often dominated by the diffusion of particles in a magnetic field composed of both a turbulent and a mean component. This process, which is two-fold turbulent mixing in that the particle motion is stochastic with respect to the field lines, needs to be understood in order to properly model cosmic-ray signatures. One of the most important aspects in the modeling of cosmic-ray diffusion is that fully resonant scattering, the most effective such process, is only possible if the wave spectrum covers the entire range of propagation angles. By taking the wave spectrum boundaries into account, we quantify cosmic-ray diffusion parallel and perpendicular to the guide field direction at turbulence levels above 5% of the total magnetic field. We apply our results of the parallel and perpendicular diffusion coefficient to the Milky Way. We show that simple purely diffusive transport is in conflict with observations of the inner Galaxy, but that just by taking a Galactic wind into account, data can be matched in the central 5 kpc zone. Further comparison shows that the outer Galaxy at $>5$kpc, on the other hand, should be dominated by perpendicular diffusion, likely changing to parallel diffusion at the outermost radii of the Milky Way.

Published in Springer Nature Applied Sciences

References in corpus (13)

• The NumPy array: a structure for efficient numerical computation
• Gamma-ray sky points to radial gradients in cosmic-ray transport
• A common solution to the cosmic ray anisotropy and gradient problems
• Propagation of high-energy cosmic rays in extragalactic turbulent magnetic fields: resulting energy spectrum and composition
• Charged particle diffusion in isotropic random magnetic fields
• A signature of anisotropic cosmic-ray transport in the gamma-ray sky
• Numerical propagation of high energy cosmic rays in the Galaxy I: technical issues
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• Relative distribution of cosmic rays and magnetic fields
• Particle Transport in intense small scale magnetic turbulence with a mean field
• Probing Intergalactic Magnetic Fields with Simulations of Electromagnetic Cascades
• MHD Turbulence, Turbulent Dynamo and Applications
• Particle scattering in turbulent plasmas with amplified wave modes

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• Efficient charged particle propagation methods
• CRPropa 3.2: a framework for high-energy astroparticle propagation