تقرير
Unstable cosmic-ray nuclei constrain low-diffusion zones in the Galactic disk
| العنوان: | Unstable cosmic-ray nuclei constrain low-diffusion zones in the Galactic disk |
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| المؤلفون: | Jacobs, Hanno, Mertsch, Philipp, Phan, Vo Hong Minh |
| سنة النشر: | 2023 |
| المجموعة: | Astrophysics |
| مصطلحات موضوعية: | Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies |
| الوصف: | Observations of the vicinity of a variety of galactic gamma-ray sources have indicated a local suppression of diffusivity of cosmic rays by up to three orders of magnitude. However, the impact of these low-diffusion zones on \emph{global} properties of cosmic-ray transport is however only poorly understood. Here, we argue that cosmic-ray 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 cosmic-ray transport model that allows for different diffusion coefficients $\kappa_{\mathrm{disk}}$ and $\kappa_{\mathrm{halo}}$ in the galactic disk and halo, respectively. Making use of preliminary data from the AMS-02 experiment on the ratio of Beryllium isotopes, we find a $3.5 \sigma$ preference for a suppression of the diffusion coefficient in the disk with a best-fit value of $\kappa_{\mathrm{disk}}/\kappa_{\mathrm{halo}} = 0.20^{+0.10}_{-0.06}$. We forecast that with upcoming data from the HELIX balloon experiment, the significance could increase to $6.8 \sigma$. Adopting a coarse-graining approach, we find that such a strong suppression could be realised if the filling fraction of low-diffusion zones in the disk was $\sim 66 \, \%$. 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 cosmic ray transport. Comment: 15 pages,10 figures, prepared for submission to MNRAS |
| نوع الوثيقة: | Working Paper |
| URL الوصول: | http://arxiv.org/abs/2305.10337 |
| رقم الأكسشن: | edsarx.2305.10337 |
| قاعدة البيانات: | arXiv |
| الوصف غير متاح. |