Highly Energetic Electrons Accelerated in Strong Solar Flares as a Preferred Driver of Sunquakes

TL;DR

This study finds that highly energetic electrons accelerated during strong solar flares are the primary drivers of sunquakes, supported by correlations between hard X-ray emissions and seismic activity.

Contribution

It provides observational evidence linking high-energy electrons to sunquake generation, supporting a recent electron-driven model and clarifying the role of energetic particles in flare-induced seismic waves.

Findings

High-energy electrons (>300 keV) are systematically associated with sunquakes.

Hard X-ray emissions correlate with white-light enhancements and seismic activity.

Downward Lorentz force can also drive sunquakes in specific cases.

Abstract

Sunquakes are enhanced seismic waves excited in some energetic solar flares. Up to now, their origin has still been controversial. In this Letter, we select and study 20 strong flares in Solar Cycle 24, whose impulse phase is fully captured by the \emph{Reuven Ramaty High Energy Solar Spectroscopic Imager} (\emph{RHESSI}). For 11 out of 12 sunquake-active flares in our sample, the hard X-ray (HXR) emission shows a good temporal and spatial correlation with the white-light (WL) enhancement and the sunquake. Spectral analysis also reveals a harder photon spectrum that extends to several hundred keV, implying a considerable population of flare-accelerated nonthermal electrons at high energies. Quantitatively, the total energy of electrons above 300 keV in sunquake-active flares is systematically different from that in sunquake-quiet flares, while the difference is marginal for electrons above 50 keV. All these facts support highly energetic electrons as a preferred driver of the sunquakes. Such an electron-driven scenario can be reasonably accommodated in the framework of a recently proposed selection rule for sunquake generation. For the remaining one event, the sunquake epicenter is cospatial with a magnetic imprint, i.e., a permanent change of magnetic field on the photosphere. Quantitative calculation shows that the flare-induced downward Lorentz force can do enough work to power the sunquake, acting as a viable sunquake driver for this specific event.