Is flux rope a necessary condition for the progenitor of coronal mass ejections?

TL;DR

This study investigates whether a magnetic flux rope is essential for the formation of coronal mass ejections, finding that some pre-eruption structures are supported by flux ropes while others are not, challenging previous assumptions.

Contribution

The paper applies an indirect magnetic field inference method to two filament events, demonstrating that flux ropes are not always necessary for CME progenitors.

Findings

One filament was supported by a magnetic flux rope.

Another filament was supported by a sheared arcade.

Flux ropes are not a necessary condition for pre-CME structures.

Abstract

A magnetic flux rope structure is believed to exist in most coronal mass ejections (CMEs). However, it has been long debated whether the flux rope exists before eruption or is formed during eruption via magnetic reconnection. The controversy has been continuing because of our lack of routine measurements of the magnetic field in the pre-eruption structure, such as solar filaments. However, recently an indirect method was proposed to infer the magnetic field configuration based on the sign of helicity and the bearing direction of the filament barbs. In this paper, we apply this method to two erupting filament events, one on 2014 September 2 and the other on 2011 March 7, and find that the first filament is supported by a magnetic flux rope and the second filament is supported by a sheared arcade, i.e., the first one is an inverse-polarity filament and the second one is a normal-polarity filament. With the identification of the magnetic configurations in these two filaments, we stress that a flux rope is not a necessary condition for the pre-CME structure.