Inferring the effective diffusion coefficient of galactic cosmic rays in the heliosheath

Journal article, 2025

The diffusion of Galactic Cosmic Rays (GCRs) into the heliosphere from the local interstellar spectrum is a stochastic process due to the scattering of particles with magnetic irregularities embedded in the solar wind. The process is influenced by energy losses and convection. Our knowledge of the solar wind turbulence properties and dynamics mostly relies on near-Earth and near-Sun observations. The solar wind turbulence behavior is still not well understood when moving far away from the inner heliosphere. Nonetheless, it is still possible to infer some information about the diffusion coefficient by directly probing GCR measurements. In this work, we model the propagation of particles through the heliosheath, i.e. between ∼ 90 AU and ∼ 120 AU distance from the Sun, solving the Parker transport equation by means of a numerical Monte Carlo technique. We apply a data-driven approach based on in situ observations from Voyager 1 in order to study the solar modulation for different particles and derive the diffusion coefficient rigidity dependence. To do this, the most abundant elements in the solar system are considered together with their corresponding isotopes. We conclude that the effective diffusion coefficient, in the energy range from 0.04 to 0.31 GeV/nuc, has a rigidity dependence of P^γ with γ∼1.42-0.42^+0.63. This result can be used to constrain the spectral behaviour of the turbulence in the heliosheath.