Some new hints on cosmic-ray propagation from AMS-02 nuclei spectra

Abstract

In this work, we considered 2 schemes (a high-rigidity break in primary source injections and a high-rigidity break in diffusion coefficient) to reproduce the newly released AMS-02 nuclei spectra (He, C, N, O, Li, Be, and B) when the rigidity larger than 50 GV. The fitting results show that current data set favors a high-rigidity break at ∼ 325 GV in diffusion coefficient rather than a break at ∼ 365 GV in primary source injections. Meanwhile, the fitted values of the factors to rescale the cosmic-ray (CR) flux of secondary species/components after propagation show us that the secondary flux are underestimated in current propagation model. It implies that we might locate in a slow diffusion zone, in which the CRs propagate with a small value of diffusion coefficient compared with the averaged value in the galaxy. Another hint from the fitting results show that extra secondary CR nuclei injection may be needed in current data set. All these new hints should be paid more attention in future research.

Hybrid Origins of the Cosmic-Ray Nucleus Spectral Hardening at a Few Hundred GV

“…Phenomenologically, in such a scenario the secondary nucleus spectra should harden even more than those of the primary ones at a few hundred GV, 3 which is equivalent to adding an extra high-rigidity break in the diffusion coefficient. Some previous works show that AMS-02 nuclei data favor the hardening coming from the propagation process rather than the CR primary source injections (see, e.g., Génolini et al 2017;Niu & Xue 2020).…”

Hybrid origins of the cosmic-ray nuclei spectral hardening at a few hundred GV

“…This result indicates that the breaks in the injection spectra of N, O, and Ne are necessary if we want to reproduce the high-rigidity hardening in these spectra. On the other hand, the concentrated distribution of ∆ν H for δ also shows its necessity to reproduce the data set, which has been proved by some of the previous works based on different configurations (see, e.g., [18,26,30]).…”

“…In such configuration, some previous works show that AMS-02 nuclei data favors the hardening coming from the propagation process rather than the CR source injection in a statistical meaning (see, e.g., Refs. [18,26]).…”

“…Moreover, the spectra of proton and He have very small uncertainties because of the extremely large event number, if one uses these spectra in the global fitting without employing independent injection spectra for them, they would seriously dilute the impacts of the real parents species' spectra (like that of C, N, O, Ne, Mg, and Si) on the daughter species' spectra (like that of Li, Be, and B) (such as in Refs. [23,26]).…”

“…The data errors used in our fitting are the quadratic sum of statistical and systematic errors. 2 The spectra of Li and Be are not used in this work because some recent works show that they might have extra primary components [23,24,26] and it needs to re-scale the production cross sections if we want to reproduce their spectra with that of B simutaneously [31,32].…”