Unstable cosmic ray nuclei constrain low-diffusion zones in the Galactic disc.
| Title: | Unstable cosmic ray nuclei constrain low-diffusion zones in the Galactic disc. |
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| Authors: | Jacobs, Hanno1 (AUTHOR) jacobs@physik.rwth-aachen.de, Mertsch, Philipp1 (AUTHOR), Phan, Vo Hong Minh1 (AUTHOR) |
| Source: | Monthly Notices of the Royal Astronomical Society. 11/21/2023, Vol. 526 Issue 1, p160-174. 15p. |
| Subject Terms: | *COSMIC rays, *BERYLLIUM isotopes, *GALACTIC halos, *DIFFUSION coefficients |
| Abstract: | Observations of the vicinity of a variety of galactic gamma-ray sources have indicated a local suppression of diffusivity of cosmic rays (CRs) by up to three orders of magnitude. However, the impact of these low-diffusion zones on global properties of CR transport is, however, only poorly understood. Here, we argue that CR nuclear ratios, like the boron-to-carbon ratio and relative abundances of Beryllium isotopes are sensitive to the filling fraction of such low-diffusion zones and hence their measurements can be used to constrain the typical sizes and ages of such regions. We have performed a careful parameter study of a CR transport model that allows for different diffusion coefficients κdisc and κhalo in the galactic disc and halo, respectively. Making use of preliminary data from the AMS-02 experiment on the ratio of Beryllium isotopes, we find a 3.5σ preference for a suppression of the diffusion coefficient in the disc with a best-fitting value of |$\kappa _{\mathrm{disc}}/\kappa _{\mathrm{halo}} = 0.20^{+0.10}_{-0.06}$|. We forecast that with upcoming data from the HELIX balloon experiment, the significance could increase to 6.8σ. Adopting a coarse-graining approach, we find that such a strong suppression could be realized if the filling fraction of low-diffusion zones in the disc was |$\sim 66~{{\ \rm per\ cent}}$|. We conclude that the impact of regions of suppressed diffusion might be larger than usually assumed and ought to be taken into account in models of Galactic CR transport. [ABSTRACT FROM AUTHOR] |
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| Database: | Academic Search Complete |
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