Local interstellar spectra and solar modulation of cosmic ray electrons and positrons

TL;DR

This study derives local interstellar spectra of cosmic ray electrons and positrons using AMS-02 and Voyager-1 data, revealing charge-sign dependent solar modulation effects and their evolution over solar cycles.

Contribution

It introduces a non-parametric method combined with a force-field model to accurately determine the LIS and solar modulation parameters for electrons and positrons.

Findings

Solar modulation parameters for positrons agree with those of nuclei.

Charge-sign dependent modulation effects are evident after magnetic field reversal.

Additional renormalization improves fit to monthly flux data.

Abstract

Low energy cosmic rays are modulated by the solar activity when they propagation in the heliosphere, leading to ambiguities in understanding their acceleration at sources and propagation in the Milky Way. By means of the precise measurements of the $e^-$, $e^+$, $e^-+e^+$, and $e^+/(e^-+e^+)$ spectra by AMS-02 near the Earth, as well as the very low energy measurements of the $e^-+e^+$ fluxes by Voyager-1 far away from the Sun, we derive the local interstellar spectra (LIS) of $e^-$ and $e^+$ components individually. Our method is based on a non-parametric description of the LIS of $e^-$ and $e^+$ and a force-field solar modulation model. We then obtain the evolution of the solar modulation parameters based on the derived LIS and the monthly fluxes of cosmic ray $e^-$ and $e^+$ measured by AMS-02. {\bf To better fit the monthly data, additional renormalization factors for $e^-$ and $e^+$ have been multiplied to the modulated fluxes.} We find that the inferred solar modulation parameters of positrons are in good agreement with that of cosmic ray nuclei, and the time evolutions of the solar modulation parameters of electrons and positrons differ after the reversal of the heliosphere magnetic field polarity, which shows clearly the charge-sign dependent modulation effect.