PSP/IS$\odot$IS Observation of a Solar Energetic Particle Event Associated With a Streamer Blowout Coronal Mass Ejection During Encounter 6

TL;DR

This study analyzes a small solar energetic particle event linked to a streamer blowout CME, revealing particle acceleration without a shock, with detailed composition and anisotropy data from the PSP spacecraft.

Contribution

First detailed in-situ observation of a small SEP event associated with a streamer blowout CME, highlighting shockless acceleration mechanisms.

Findings

Particles mainly streaming outward from the Sun.

Event associated with a slow SBO-CME without a shock.

Detection of heavy ions like O and Fe without significant 3He or energetic electrons.

Abstract

In this paper we examine a low-energy SEP event observed by IS$\odot$IS's Energetic Particle Instrument-Low (EPI-Lo) inside 0.18 AU on September 30, 2020. This small SEP event has a very interesting time profile and ion composition. Our results show that the maximum energy and peak in intensity is observed mainly along the open radial magnetic field. The event shows velocity dispersion, and strong particle anisotropies are observed throughout the event showing that more particles are streaming outward from the Sun. We do not see a shock in the in-situ plasma or magnetic field data throughout the event. Heavy ions, such as O and Fe were detected in addition to protons and 4He, but without significant enhancements in 3He or energetic electrons. Our analysis shows that this event is associated with a slow streamer-blowout coronal mass ejection (SBO-CME) and the signatures of this small CME event are consistent with those typical of larger CME events. The time-intensity profile of this event shows that PSP encountered the western flank of the SBO-CME. The anisotropic and dispersive nature of this event in a shockless local plasma give indications that these particles are most likely accelerated remotely near the Sun by a weak shock or compression wave ahead of the SBO-CME. This event may represent direct observations of the source of low-energy SEP seed particle population.