Parker Solar Probe Observations of Energetic Particles in the Flank of a Coronal Mass Ejection Close to the Sun

TL;DR

This study reports Parker Solar Probe observations of energetic particles around a CME near the Sun, revealing flux ropes, particle acceleration, and trapping mechanisms within the CME structure.

Contribution

First detailed in situ analysis of energetic particles and magnetic structures in the flank of a CME close to the Sun, highlighting particle acceleration and confinement processes.

Findings

Flux ropes within the CME show flare-like signatures.

Energetic particles are most enhanced within the CME, indicating local acceleration.

CME acts as a trap and accelerator for energetic particles.

Abstract

We present an event observed by Parker Solar Probe at $\sim$0.2 au on March 2, 2022 in which imaging and \emph{in situ} measurements coincide. During this event, PSP passed through structures on the flank of a streamer blowout CME including an isolated flux tube in front of the CME, a turbulent sheath, and the CME itself. Imaging observations and \emph{in situ} helicity and principal variance signatures consistently show the presence of flux ropes internal to the CME. In both the sheath, and the CME interval, the distributions are more isotropic, the spectra are softer, and the abundance ratios of Fe/O and He/H are lower than those in the isolated flux tube, and yet elevated relative to typical plasma and SEP abundances. These signatures in the sheath and the CME indicate that both flare populations and those from the plasma are accelerated to form the observed energetic particle enhancements. In contrast, the isolated flux tube shows large streaming, hard spectra and large Fe/O and He/H ratios, indicating flare sources. Energetic particle fluxes are most enhanced within the CME interval from suprathermal through energetic particle energies ($\sim$ keV to $>10$ MeV), indicating particle acceleration, and confinement local to the closed magnetic structure. The flux-rope morphology of the CME helps to enable local modulation and trapping of energetic particles, particularly along helicity channels and other plasma boundaries. Thus, the CME acts to build-up energetic particle populations, allowing them to be fed into subsequent higher energy particle acceleration throughout the inner heliosphere where a compression or shock forms on the CME front.