The B/C and sub-Iron/Iron Cosmic ray ratios - further evidence in favor of the spiral arm diffusion model

Abstract

The Boron to Carbon (B/C) and sub-Fe/Fe ratios provides an important clue on Cosmic Ray (CR) propagation within the Galaxy. These ratios estimate the grammage that the CR traverse as they propagate from their sources to Earth. Attempts to explain these ratios within the standard CR propagation models require ad hoc modifications and even with those these models necessitate inconsistent grammages to explain both ratios. As an alternative, physically motivated model, we have proposed that CR originate preferably within the galactic spiral arms. CR propagation from dynamic spiral arms has important imprints on various secondary to primary ratios, such as the B/C ratio and the positron fraction. We use our spiral arm diffusion model with the spallation network extended up to Nickel to calculate the sub-Fe/Fe ratio. We show that without any additional parameters the spiral arm model consistently explains both ratios with the same grammage, providing further evidence in favor of this model.

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• SkyFACT: High-dimensional modeling of gamma-ray emission with adaptive templates and penalized likelihoods
• Electron and positron spectra in the three dimensional spatial-dependent propagation model
• Reconciling the diffuse Galactic gamma-ray and the cosmic ray spectra
• The consequence of a new ISRF model of the Milky Way on predictions for diffuse gamma-ray emission
• Lower limits on the nucleosynthezis of ${}^{44}$Ti and ${}^{60}$Fe in the dynamic spiral-arms model
• Electron-Capture Isotopes could Constrain Cosmic-Ray Propagation Models