Acceleration of relativistic electron beams by a strong interplanetary shock at 1 AU
Résumé
Collisionless shocks in the heliosphere such as planetary bow shocks and CME-driven shocks play a significant role as particle accelerators. These shocks can be categorized based on their geometry relative to the magnetic field as parallel, perpendicular, or oblique. With a profound impact on the surrounding plasma, shock waves exhibit intricate and dynamic evolution across multiple scales. Of particular interest are the "super-critical" interplanetary traveling shocks and the acceleration of energetic electrons, where understanding remains incomplete due to scale-related challenges and technical complexities. On July 25, 2022, Solar Orbiter encountered the strongest shock so far in its mission and the associated energetic storm particles. The event featured intriguing phenomena, including upstream field-aligned relativistic electron beams, large-scale magnetic field rotations, and a delayed downstream particle flux. Our focus lies on elucidating the role of the large-scale magnetic rotations in shock corrugations and their effects on energetic particles. The observations strongly support a scenario in which the curvatures arising from these corrugations act as the source for the field-aligned relativistic beams of electrons. Further exploitation of the observation such as the peak energy spectra have provided critical insights into the acceleration mechanisms as well as the transport processes close to the origin of the upstream electron beam.
