Origin of Coronal Extreme Ultraviolet Shockwaves without a Coronal Mass Ejection Event

TL;DR

This study investigates the origins of EUV shockwaves in the solar corona, comparing events with and without CMEs to understand the mechanisms behind sunquake generation and coronal wave propagation.

Contribution

It provides observational evidence distinguishing coronal waves associated with CMEs from those without, highlighting differences in speed, impulsiveness, and energy characteristics.

Findings

CME-associated coronal waves propagate faster.

Standalone flares are less impulsive and energetic than sunquake flares.

CME-related waves have higher volume emission measures.

Abstract

A leading theory of sunquake generation involves flare-accelerated particles depositing energy into the photosphere. Simulations of sunquake excitation suggest co-excitation with wavefronts propagating in the corona and chromosphere, similar to Moreton-Ramsey waves, and large-scale coronal propagating fronts (LCPFs). To investigate observational evidence for the particle-driven mechanism in LCPFs, we compare populations of events associated with and without coronal mass ejections (CMEs). CMEs are known to generate similar EUV shock waves. We employ a visual inspection of flare events that generate LCPFs using Atmospheric Imaging Assembly (AIA) and Large Angle and Spectrometric Coronagraph (LASCO) coronagraph images to find that coronal waves associated with CMEs propagate noticeably faster. Then we examine GOES soft X-ray (SXR) data of standalone flare events (those that generate coronal waves without CMEs), focusing on soft X-ray (SXR) characteristics related to magnetic energy release rate. This reveals that such standalone or confined flares differ from sunquake flares: they are less impulsive and energetic than sunquake flares. However, they are more impulsive but less energetic than LCPF-associated flares with a CME. In particular, coronal waves accompanied by CMEs exhibit significantly higher volume emission measures, suggesting a different generation mechanism.