Exploring particle acceleration dynamics in the vicinity of ICME shocks: insights from superposed epoch analysis

ABSTRACT How nature accelerates particles is a primary problem in astro and space plasma physics. Despite numerous models and theories attempting to explain particle acceleration mechanisms, observational verification within these frameworks remains limited. Single-event observational studies suggest that interplanetary coronal mass ejection (ICME) shocks play an active role in particle acceleration. Therefore, to discover the generalized features, we conduct a superposed epoch analysis of 45 ICME shocks to investigate the relative enhancement of low-energy electron and ion flux measured by Advanced Composition Explorer/Electron, Proton, and Alpha-Particle Monitor. Our observations reveal that the average maximum enhancement of electrons and ions occurs concurrently with the onset of the ICME shock. Furthermore, our analysis uncovers distinct average responses of electrons and protons/ions in the 12 hours before and after the shock. This nuanced exploration provides additional insights into the complex dynamics of particle acceleration during ICME shocks, shedding light on the differing behaviours of ions and electrons near the shock front.