Unusual Circumstances of the 2024 June 8 GLE

TL;DR

The 2024 June 8 GLE event was unusual because it lacked associated sustained gamma-ray emission despite typical phenomena like a fast CME and major flare, possibly due to east-west asymmetry in particle flow.

Contribution

This study reports the first GLE event in 2024 without associated SGRE, highlighting potential asymmetry effects in particle acceleration.

Findings

GLE occurred without SGRE despite typical associated phenomena

East-west asymmetry likely caused the absence of SGRE

Event featured a fast, wide CME and intense solar flare

Abstract

Ground Level Enhancement (GLE) in large solar energetic particle (SEP) events is indicative of protons accelerated to GeV energies. Almost all GLE events are associated with sustained gamma-ray emission (SGRE) from the Sun because the latter require >300 MeV protons that are readily present during GLEs. Here we report on the 2024 June 8 GLE event, which has the distinction of not being associated with an SGRE event. All the associated phenomena typical of SGRE events were present: a fast and wide CME, a major solar flare, and an intense type II radio bursts that extend from the metric to kilometric wavelength domains. There was a data gap of ~51 min, but the SGRE is expected to last for hours. We suggest the east-west asymmetry in the flow of energetic particles from the shock is likely to be the reason for the lack of SGRE emission.