Observations of Forbush Decreases of cosmic ray electrons and positrons with the Dark Matter Particle Explorer

TL;DR

This study analyzes Forbush Decreases of cosmic ray electrons and positrons using data from the Dark Matter Particle Explorer, revealing energy-dependent effects and solar energetic particle events in 2017.

Contribution

First detailed space-based observation of electron and positron Forbush Decreases across 2-20 GeV energy range with high time resolution.

Findings

Detected two solar energetic particle events not seen in neutron monitor data.

Observed energy-dependent amplitude and recovery times of cosmic ray fluxes.

Provided new insights into interplanetary disturbances caused by CMEs.

Abstract

The Forbush Decrease (FD) represents the rapid decrease of the intensities of charged particles accompanied with the coronal mass ejections (CMEs) or high-speed streams from coronal holes. It has been mainly explored with ground-based neutron monitors network which indirectly measure the integrated intensities of all species of cosmic rays by counting secondary neutrons produced from interaction between atmosphere atoms and cosmic rays. The space-based experiments can resolve the species of particles but the energy ranges are limited by the relative small acceptances except for the most abundant particles like protons and helium. Therefore, the FD of cosmic ray electrons and positrons have just been investigated by the PAMELA experiment in the low energy range ($<5$ GeV) with limited statistics. In this paper, we study the FD event occurred in September, 2017, with the electron and positron data recorded by the Dark Matter Particle Explorer. The evolution of the FDs from 2 GeV to 20 GeV with a time resolution of 6 hours are given. We observe two solar energetic particle events in the time profile of the intensity of cosmic rays, the earlier and weak one has not been shown in the neutron monitor data. Furthermore, both the amplitude and recovery time of fluxes of electrons and positrons show clear energy-dependence, which is important in probing the disturbances of the interplanetary environment by the coronal mass ejections.