HelMod in the Works: From Direct Observations to the Local Interstellar Spectrum of Cosmic-Ray Electrons

Area of Science:

• Astrophysics
• Cosmic Ray Physics
• Heliophysics

Background:

• The local interstellar spectrum (LIS) of cosmic-ray (CR) electrons is crucial for understanding particle propagation in the Galaxy and heliosphere.
• Previous models faced challenges in reconciling low- and high-energy electron observations and solar modulation effects.

Purpose of the Study:

• To derive a comprehensive and accurate LIS of CR electrons from 1 MeV to 1 TeV.
• To integrate state-of-the-art CR propagation models (GALPROP and HelMod) with recent experimental data.
• To develop a robust method for parameter optimization and model refinement.

Main Methods:

• Combined GALPROP and HelMod propagation packages into a unified framework.
• Employed an iterative maximum-likelihood method for parameter optimization using extensive proton spectra data (1997-2015).
• Validated the model against diverse CR electron measurements (Voyager 1, PAMELA, AMS-02) and Ulysses data.

Main Results:

• Developed a refined CR electron LIS that harmonizes low-energy (Voyager 1) and high-energy (PAMELA, AMS-02) interstellar spectra.
• Successfully accounted for solar magnetic field polarities and Ulysses out-of-ecliptic measurements.
• Derived interstellar and heliospheric propagation parameters consistent with previous findings for other CR species.

Conclusions:

• The refined CR electron LIS provides a more accurate representation of the local interstellar environment.
• The integrated modeling approach demonstrates robustness in describing CR propagation across different energies and heliospheric conditions.
• The derived propagation parameters offer valuable insights into galactic and heliospheric processes affecting cosmic rays.