Reconciling Observational Challenges to the Impulsive-Piston Shock-Excitation Scenario. I. Kinematic Challenges

Abstract

Until now, there is no consensus on the origin of coronal shock waves. Questions also remain about the patterns that govern the propagation of the presumably related disturbances observed in the extreme ultraviolet (EUV waves). We present arguments in favor of the initial excitation of the waves by the impulsive acceleration of erupting structures. We consider two puzzling events that have been known thanks to the efforts of different research teams. Using recent findings and our methods, we aim to determine what might actually have happened in these challenging events. In the first event, the expansion of the coronal mass ejection (CME) was determined by gravity starting from the low corona. The previous analysis led the authors to conclude about the flare-related origin of the associated shock wave. We also consider another event, in which an EUV wave had a strange kinematics. This was one of the weakest flares accompanied by EUV waves. Both of these challenging events have been reconciled in terms of an impulsively excited piston shock.