Genesis and impulsive evolution of the 2017 September 10 coronal mass ejection

TL;DR

This study investigates the genesis and impulsive evolution of the 2017 September 10 coronal mass ejection using multi-wavelength observations, revealing the role of magnetic reconnection and flux addition in its rapid acceleration and morphology.

Contribution

It provides new insights into the magnetic structure, impulsive dynamics, and the role of reconnection in the evolution of a very fast CME, challenging traditional three-part CME models.

Findings

Hot cavity rim indicates poloidal flux addition via reconnection.

CME shell develops from large active region loops and evolves into the CME front.

Impulsive accelerations correlate with flare hard X-ray bursts.

Abstract

The X8.2 event of 10 September 2017 provides unique observations to study the genesis, magnetic morphology and impulsive dynamics of a very fast CME. Combining GOES-16/SUVI and SDO/AIA EUV imagery, we identify a hot ($T\approx 10-15$ MK) bright rim around a quickly expanding cavity, embedded inside a much larger CME shell ($T\approx 1-2$ MK). The CME shell develops from a dense set of large AR loops ($\gtrsim$0.5 $R_s$), and seamlessly evolves into the CME front observed in LASCO C2. The strong lateral overexpansion of the CME shell acts as a piston initiating the fast EUV wave. The hot cavity rim is demonstrated to be a manifestation of the dominantly poloidal flux and frozen-in plasma added to the rising flux rope by magnetic reconnection in the current sheet beneath. The same structure is later observed as the core of the white light CME, challenging the traditional interpretation of the CME three-part morphology. The large amount of added magnetic flux suggested by these observations explains the extreme accelerations of the radial and lateral expansion of the CME shell and cavity, all reaching values of $5 - 10$ km s$^{-2}$. The acceleration peaks occur simultaneously with the first RHESSI $100-300$ keV hard X-ray burst of the associated flare, further underlining the importance of the reconnection process for the impulsive CME evolution. Finally, the much higher radial propagation speed of the flux rope in relation to the CME shell causes a distinct deformation of the white light CME front and shock.