Partial Null Point Reconnection of an Eruptive Filament

TL;DR

This paper analyzes a solar filament eruption on 13 July 2015, highlighting partial null-point reconnection, flux rope dynamics, and associated flare and CME phenomena, providing insights into the magnetic reconnection processes involved.

Contribution

It presents detailed observations of a null-point topology and interchange reconnection during a filament eruption, advancing understanding of magnetic reconnection in solar eruptions.

Findings

Null-point topology confirmed by potential-field extrapolation

Eruption involved interchange reconnection with open magnetic fields

CME exhibited classical flux rope shape and open field plasma ejection

Abstract

Solar filaments are cool and dense plasma structures suspended in the solar corona against gravity. We present observations of a quiescent filament eruption that occurs on 13 July 2015. The eruption is associated with a two-ribbon GOES B8.9 class flare. Photospheric magnetic flux cancellation is present below the filament during days. This builds up a flux rope which progressively rises until it gets unstable, first leading to a confined eruption and pre-flare brightenings, then to an ejection which starts $\approx$ 20 min later with the flare onset. An interesting feature of this event is the presence of a large circular brightening formed around the erupting region. This brightening is produced due to interchange reconnection of the ejected magnetic configuration with the surrounding open magnetic field. This null-point topology is confirmed by a potential-field extrapolation. The EUV loops located on the southern side of the filament eruption first contract during the null-point reconnection, then expand as the flux rope is ejected. The associated CME has both a classical flux rope shape and plasma ejected along open field lines on the flux rope side (a trace of interchange reconnection). Finally, we set all this disparate observations within a coherent framework where magnetic reconnection occurs both below and above the erupting filament.