GeV Particle Acceleration in Solar Flares and Ground Level Enhancement (GLE) Events

Abstract

{\sl Ground Level Enhancement (GLE)} events represent the largest class of {\sl solar energetic particle (SEP)} events that require acceleration processes to produce $\gapprox 1$ GeV ions in order to produce showers of secondary particles in the Earth's atmosphere with sufficient intensity to be detected by ground-level neutron monitors, above the background of cosmics rays. Although the association of GLE events with both solar flares and coronal mass ejections (CMEs) is undisputed, the question arises about the location of the responsible acceleration site: coronal flare sites or heliospheric CME-associated shocks? To investigate the first possibility we explore the timing of GLE events with respect to hard X-ray production in solar flares, considering the height and magnetic topology of flares, the role of extended acceleration, and particle trapping. We find that 50% (6 out of 12) of recent (non-occulted) GLE events are accelerated during the impulsive flare phase, while the remaining half are accelerated significantly later. It appears that the prompt GLE component, which is observed in virtually all GLE events, is caused by flare-accelerated particles in the lower corona, while the delayed gradual GLE component can be produced by both, either by extended acceleration and/or trapping in flare sites, or by particles accelerated in CME-associated shocks during their propagation through the heliosphere.

8 Figures, 3 Tables, subm. to SPACE SCIENCE REVIEWS, Topical Issue on GLE, accepted 2011 December 20; in press

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• The magnetic connectivity of coronal shocks from behind-the-limb flares to the visible solar surface during $\gamma$-ray events
• Scaling Relations in Coronal Mass Ejections and Energetic Proton Events associated with Solar Superflares
• Relations between Microwave Bursts and near-Earth High-Energy Proton Enhancements and their Origin
• Analysis of the ground level enhancements on 14 July 2000 and on 13 December 2006 using neutron monitor data
• Correcting for interplanetary scattering in velocity dispersion analysis of solar energetic particles
• Evidence for a Coronal Shock Wave Origin for Relativistic Protons Producing Solar Gamma-Rays and Observed by Neutron Monitors at Earth
• Radio, Hard X-Ray, and Gamma-Ray Emissions Associated with a Far-Side Solar Event
• An Updated View of Solar Eruptive Flares and Development of Shocks and CMEs: History of the 2006 December 13 GLE-Productive Extreme Event
• Small electron acceleration episodes in the solar corona
• The 26 December 2001 Solar Eruptive Event Responsible for GLE63. II. Multi-Loop Structure of Microwave Sources in a Major Long-Duration flare
• The 26 December 2001 Solar Eruptive Event Responsible for GLE63. III. CME, Shock Waves, and Energetic Particles
• Relations between strong high-frequency microwave bursts and proton events
• On some features of the solar proton event on 2021 October 28 (GLE73)
• Signals at ground level of relativistic solar particles associated to the "All Saints" filament eruption on 2014
• The 26 December 2001 Solar Event Responsible for GLE63. I. Observations of a Major Long-Duration Flare with the Siberian Solar Radio Telescope
• Relationship between Intensity of White-Light Flares and Proton Flux of Solar Energetic Particles
• Relationship of peak fluxes of solar radio bursts and X-ray class of solar flares: Application to early great solar flares
• Relationship between solar energetic particle intensities and coronal mass ejection kinematics using STEREO/SECCHI field of view