PoS - Proceedings of Science
Volume 444 - 38th International Cosmic Ray Conference (ICRC2023) - Cosmic-Ray Physics (Direct, CRD)
Unstable cosmic-ray nuclei constrain low-diffusion zones in the galactic disk
H. Jacobs*, P. Mertsch and V.H.M. Phan
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Pre-published on: July 25, 2023
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Several recent observations in the vicinity of cosmic ray sources hint at a local diffusivity, which is about two to three orders of magnitude lower than the global average. The exact filling fraction of these zones is unclear. We show that secondary to primary and stable to unstable ratios together are sensitive to the presence these zones. We have developed a semi-analytical model of galactic cosmic ray transport with two distinct diffusion regimes, with an on average suppressed value of $\kappa_{\mathrm{disk}}$ in the disk compared to the one in the halo, $\kappa_{\mathrm{halo}}$ and use this to evaluate the $\mathrm{B/C}$ and $\mathrm{^{10}Be/^9Be}$ ratios. Making use of preliminary AMS-02 data we find a best fit value of $\kappa_{\mathrm{disk}}/\kappa_{\mathrm{halo}} = 0.20^{+0.10}_{-0.06}$ with $3.5\,\sigma$. If upcoming HELIX data follow the same trend, the significance could be increased to $6.8\,\sigma$. Adopting a coarse-graining approach, we find the suppression corresponds to filling fraction of $\sim 66 \, \%$. We conclude that regions of suppressed diffusion might be larger than usually assumed and ought to be taken into account in models of Galactic cosmic ray transport.
DOI: https://doi.org/10.22323/1.444.0104
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