Electron and proton acceleration during the first ground level enhancement of solar cycle 24

TL;DR

This study investigates the sources and timing of electron and proton acceleration during the first ground level enhancement of solar cycle 24, combining in situ measurements, remote solar observations, and modeling to identify acceleration mechanisms.

Contribution

It provides a comprehensive analysis of particle acceleration sources during the GLE event, integrating multi-instrument data and modeling to distinguish flare and CME-driven shock contributions.

Findings

Electrons were impulsively injected during flare activity, consistent with non-thermal emissions.

Relativistic protons were released approximately 10 minutes after electrons, likely accelerated by CME-driven shocks.

Protons with ~1.12 GeV energy were probably accelerated by CME shocks at 3.07 solar radii.

Abstract

High-energy particles were recorded by near-Earth spacecraft and ground-based neutron monitors (NMs) on 2012 May 17. This event was the first ground level enhancement (GLE) of solar cycle 24. In this study, we try to identify the acceleration source(s) of solar energetic particles by combining in situ particle measurements from the WIND/3DP, GOES 13, and solar cosmic rays registered by several NMs, as well as remote-sensing solar observations from SDO/AIA, SOHO/LASCO, and RHESSI. We derive the interplanetary magnetic field (IMF) path length (1.25 +/- 0.05 AU) and solar particle release time (01:29 +/- 00:01 UT) of the first arriving electrons by using their velocity dispersion and taking into account contamination effects. We found that the electron impulsive injection phase, indicated by the dramatic change in the spectral index, is consistent with flare non-thermal emission and type III radio bursts. Based on the potential field source surface concept, modeling of the open-field lines rooted in the active region has been performed to provide escape channels for flare-accelerated electrons.Meanwhile, relativistic protons are found to be released 10 minutes later than the electrons, assuming their scatter-free travel along the same IMF path length. Combining multi-wavelength imaging data of the prominence eruption and coronal mass ejection (CME), we obtain evidence that GLE protons, with an estimated kinetic energy of 1.12 GeV, are probably accelerated by the CME-driven shock when it travels to 3.07 solar radii. The time-of-maximum spectrum of protons is typical for shock wave acceleration.