Solar energetic particles inside a coronal mass ejection event observed with the ACE spacecraft

Abstract

In this work, solar flare energetic particle fluxes (E e ⩾38 keV) observed by the EPAM experiment aboard ACE are utilized as diagnostics of the large-scale structure and topology of the interplanetary magnetic field (IMF) embedded within a well-identified interplanetary coronal mass ejection (ICME). The still controversial question of whether the detected ICME structure has been detached from the solar corona or is still magnetically anchored to it is addressed. The observation of two impulsive solar flare electron events inside the ICME suggests that field lines in this ICME are rooted at the Sun. From the time evolution of the angular distributions of the particle intensities we infer that the observations are consistent with the magnetic topology of a magnetic bottle between a magnetic mirror located at the Sun and a magnetic constriction upstream from ACE formed by the convergence of open field lines that reflects the outgoing electrons. The magnetic mirror strength is calculated in one case based upon the local IMF observations and the electron event onset characteristics. A magnetic field enhancement observed by ACE in the downstream region of the CME-driven shock is identified as the agent responsible for the mirroring of the energetic electrons.