Investigating the Uniqueness and Causal Relationship of Precursor Activity to Solar Energetic Events

The physical role played by small-scale activity that occurs before the sudden onset of solar energetic events (SEEs, i.e., solar flares and coronal mass ejections) remains in question, in particular as related to SEE initiation and early evolution.  It is still unclear whether such precursor activity, often interpreted as plasma heating, particle acceleration, or early filament activation, is indicative of a pre-event phase or simply on-going background activity.

In this contribution we investigate the uniqueness and causal connection between precursors and SEEs using paired activity-quiet epochs. We focus on transient brightenings (TBs) and present analysis regimes to study their role as precursors, including imaging of the solar atmosphere, magnetic field, and topology analysis using archive data from the Atmospheric Imaging Assembly and the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory. Applying these methods qualitatively to three cases, we find that prior to solar flares, TBs 1) tend to occur in one large cluster close to the future flare location and below the separatrix surface of a coronal null point, 2) are co-spatial with reconnection signatures in the lower solar atmosphere, such as bald patches and null point fan traces and 3) cluster in the vicinity of strong-gradient polarity inversion lines and regions of increased excess magnetic energy density. TBs are also observed during quiet epochs (i.e., no SEE activity) of the same active regions, but they appear in smaller clusters not following a clear spatial pattern, although sometimes associated with short, spatially-intermittent bald patches and fan traces, but predominantly away from strong gradient polarity inversion lines in areas with little excess energy density.