Transport parameters from AMS-02 F/Si data and fluorine source abundance

¹ Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
² LPSC, Université Grenoble Alpes, CNRS/IN2P3, 53 Avenue des Martyrs, 38026 Grenoble, France
e-mail: david.maurin@lpsc.in2p3.fr
³ LAPTh, Université Savoie Mont Blanc & CNRS, Chemin de Bellevue, 74941 Annecy Cedex, France
⁴ Université Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France

Received: 2 August 2022
Accepted: 27 April 2024

Abstract

Context. The AMS-02 collaboration recently released cosmic ray F/Si data with an unprecedented accuracy. Cosmic ray fluorine is predominantly produced by fragmentation of heavier progenitors, while silicon is mostly accelerated at source. This ratio is thus maximally sensitive to cosmic ray propagation.

Aims. We study the compatibility of the transport parameters derived from the F/Si ratio with those obtained from the lighter Li/C, Be/C, and B/C ratios. We also inspect the cosmic ray source abundance of F, which is one of the few elements that has a high first ionisation potential but is only moderately volatile and is a potentially key element to study the acceleration mechanism of cosmic rays.

Methods. We used the 1D diffusion model implemented in the USINE code and performed χ² analyses accounting for several systematic effects (energy correlations in data, nuclear cross sections, and solar modulation uncertainties). We also took advantage of the EXFOR nuclear database to update the F production cross sections for its most important progenitors (identified to be ⁵⁶Fe, ³²S, ²⁸Si, ²⁷Al, ²⁴Mg, ²²Ne, and ²⁰Ne).

Results. The transport parameters obtained from AMS-02 F/Si data are compatible with those obtained from AMS-02 (Li,Be,B)/C data. The combined fit of all of these ratios leads to a χ_min²/d.o.f. ≈ 1.1, with ≲10% adjustments of the B and F production cross sections (which are based on very few nuclear data points and would strongly benefit from new measurements). The F/Si ratio is compatible with a pure secondary origin of F, with a best-fit relative source abundance (¹⁹F/²⁸Si)_CRS ∼ 10⁻³ and an upper limit of ∼5 × 10⁻³. Unfortunately, this limit is not sufficient to test global acceleration models of cosmic ray nuclei, for which values at the level of ∼10⁻⁴ are required. Such levels could be attained with F/Si data with a few percent of accuracy at a few tens of TV, which is possibly within reach for the next generation of cosmic ray experiments.