Formation of the cosmic-ray halo: Galactic spectrum of primary cosmic rays

Abstract

A self-consistent model of a one-dimensional cosmic-ray (CR) halo around the Galactic disk is formulated with the restriction to a minimum number of free parameters. It is demonstrated that the turbulent cascade of MHD waves does not necessarily play an essential role in the halo formation. Instead, an increase of the Alfven velocity with distance to the disk leads to an efficient generic mechanism of the turbulent redshift, enhancing CR scattering by the self-generated MHD waves. As a result, the calculated size of the CR halo at lower energies is determined by the halo sheath, an energy-dependent region around the disk beyond which the CR escape becomes purely advective. At sufficiently high energies, the halo size is set by the characteristic thickness of the ionized gas distribution. The calculated Galactic spectrum of protons shows a remarkable agreement with observations, reproducing the position of spectral break at ~ 0.6 TeV and the spectral shape up to ~ 10 TeV.

10 pages, 3 figures; accepted for publication in ApJ

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• Lévy Flights and Leaky Boxes: Anomalous Diffusion of Cosmic Rays
• Sources and Radiations of the Fermi Bubbles
• Hydrodynamic model of nonthermal emission from the Fermi bubbles
• Constraining the cosmic ray propagation halo thickness using Fermi-LAT observations of high-latitude clouds