In situ Observations of Ultra-Relativistic ElectronAcceleration in the Fastest Heliospheric Shock Wave by Parker Solar Probe

Abstract

Collisionless shock waves (CSWs) in plasma, prevalent in diverse astrophysical contexts, are key to understanding cosmic particle acceleration. These shock waves, observable in environments from heliospheric planetary bow shocks to supernova remnants (SNRs), efficiently convert kinetic energy to thermal energy and accelerate particles to sub-relativistic and relativistic energies. A particular focus is on electrons accelerated by these shocks, as they generate electromagnetic radiation, making astrophysical shocks like SNRs observable. Despite their significance, gaps remain in our understanding of the dynamic mechanisms behind these universal accelerators, underscoring the necessity for in-depth, direct in situ measurements. Heliospheric shocks offer a unique opportunity for such in situ studies, particularly those that are strong and fast, potentially mirroring SNR shocks. This study highlights the groundbreaking in situ observations of the fastest heliospheric shock wave yet, traveling at nearly 1% the speed of light, captured by the pioneering Parker Solar Probe. Positioned just 0.23 astronomical units from the Sun, the probe directly measured the acceleration of electrons and ions to high energies amidst intense electromagnetic activity. A landmark discovery was the acceleration of electrons to ultra-relativistic speeds, with energies reaching up to 6 Million electron volts (MeV). This observation not only provides unprecedented insights into the mechanisms of particle acceleration in CSWs but also bridges the gap in our understanding of similar processes in more distant astrophysical phenomena like SNRs. The findings from the Parker Solar Probe open new avenues for exploring and comprehending the intricate processes of cosmic particle acceleration.