Large Solar Energetic Particle Events Associated with Filament Eruptions Outside of Active Regions

TL;DR

This study analyzes four large filament eruptions from solar cycles 23 and 24, revealing that fast CMEs and shock formation beyond 2-3 solar radii are key factors in associated large SEP events, regardless of flare intensity.

Contribution

It demonstrates that large SEP events linked to filament eruptions outside active regions are primarily driven by fast CMEs and shocks forming at greater heights, challenging the emphasis on flares.

Findings

Fast CMEs (~1000 km/s) are associated with large SEP events.

Shocks often form beyond 2-3 solar radii, with few metric type II bursts.

Flare intensity and type III burst duration are less significant in these SEP events.

Abstract

We report on four large filament eruptions (FEs) from solar cycles 23 and 24 that were associated with large solar energetic particle (SEP) events and interplanetary type II radio bursts. The post-eruption arcades corresponded to mostly C-class soft X-ray enhancements, but an M1.0 flare was associated with one event. However, the associated coronal mass ejections (CMEs) were fast (speeds about 1000 km/s) and appeared as halo CMEs in the coronagraph field of view. The interplanetary type II radio bursts occurred over a wide wavelength range indicating the existence of strong shocks throughout the inner heliosphere. No metric type II bursts were present in three events, indicating that the shocks formed beyond 2 to 3 Rs. In one case, there was a metric type II burst with low starting frequency indicating a shock formation height of about 2 Rs. The FE-associated SEP events did have softer spectra (spectral index greater than 4) in the 10 to 100 MeV range, but there were other low-intensity SEP events with spectral indices >/=4. Some of these events are likely FE-SEP events, but were not classified so in the literature because they occurred close to active regions. Some were definitely associated with large active region flares, but the shock formation height was large. We definitely find a diminished role for flares and complex type III burst durations in these large SEP events. Fast CMEs and shock formation at larger distances from the Sun seem to be the primary characteristics of the FE-associated SEP events.