HelMod in the works: from direct observations to the local interstellar spectrum of cosmic-ray electrons

TL;DR

This paper develops a comprehensive method combining GALPROP and HelMod models to accurately derive the local interstellar spectrum of cosmic-ray electrons across a broad energy range, integrating multiple observational data sets.

Contribution

It introduces an iterative maximum-likelihood approach to refine cosmic-ray electron LIS by jointly optimizing propagation parameters using diverse experimental data.

Findings

The derived LIS fits Voyager 1, PAMELA, and AMS-02 data.

The method successfully accounts for solar modulation effects.

Propagation parameters align with previous proton and helium studies.

Abstract

The local interstellar spectrum (LIS) of cosmic-ray (CR) electrons for the energy range 1 MeV to 1 TeV is derived using the most recent experimental results combined with the state-of-the-art models for CR propagation in the Galaxy and in the heliosphere. Two propagation packages, GALPROP and HelMod, are combined to provide a single framework that is run to reproduce direct measurements of CR species at different modulation levels, and at both polarities of the solar magnetic field. An iterative maximum-likelihood method is developed that uses GALPROP-predicted LIS as input to HelMod, which provides the modulated spectra for specific time periods of the selected experiments for model-data comparison. The optimized HelMod parameters are then used to adjust GALPROP parameters to predict a refined LIS with the procedure repeated subject to a convergence criterion. The parameter optimization uses an extensive data set of proton spectra from 1997-2015. The proposed CR electron LIS accommodates both the low-energy interstellar spectra measured by Voyager 1 as well as the high-energy observations by PAMELA and AMS-02 that are made deep in the heliosphere; it also accounts for Ulysses counting rate features measured out of the ecliptic plane. The interstellar and heliospheric propagation parameters derived in this study agree well with our earlier results for CR protons, helium nuclei, and anti-protons propagation and LIS obtained in the same framework.