WISPR Imaging of a Pristine CME

TL;DR

This paper reports on WISPR observations of a slow CME on 2018 November 01, comparing it with LASCO and EUV data to analyze its structure and evolution from the low corona into the heliosphere.

Contribution

It provides the first detailed WISPR imaging of a CME, linking EUV features to white-light observations and identifying the CME core as a pre-existing magnetic flux rope.

Findings

WISPR observed a slow CME consistent with streamer blowout characteristics.

EUV data revealed a pre-eruption structure that corresponds to the CME core.

The event's weakness allowed for clear observation of the flux rope structure.

Abstract

The Wide-field Imager for Solar Probe (WISPR) on board the Parker Solar Probe (PSP) observed a CME on 2018 November 01, the first day of the initial PSP encounter. The speed of the CME, approximately 200-300 km s$^{-1}$ in the WISPR field of view, is typical of slow, streamer blowout CMEs. This event was also observed by the LASCO coronagraphs. WISPR and LASCO view remarkably similar structures that enable useful cross-comparison between the two data sets as well as stereoscopic imaging of the CME. Analysis is extended to lower heights by linking the white-light observations to EUV data from AIA, which reveal a structure that erupts more than a full day earlier before the CME finally gathers enough velocity to propagate outward. This EUV feature appears as a brightness enhancement in cooler temperatures such as 171 \AA, but as a cavity in nominal coronal temperatures such as 193 \AA. By comparing this circular, dark feature in 193 \AA \ to the dark, white-light cavity at the center of the eruption in WISPR and LASCO, it can be seen that this is one coherent structure that exists prior to the eruption in the low corona before entering the heliosphere and likely corresponds to the core of the magnetic flux rope. It is also believed that the relative weakness of the event contributed to the clarity of the flux rope in WISPR, as the CME did not experience impulsive forces or strong interaction with external structures that can lead to more complex structural evolution.