Eruptive-Impulsive Homologous M-class Flares Associated with Double-Decker Flux Rope Configuration in Mini-Sigmoid of NOAA 12673

TL;DR

This study analyzes homologous impulsive M-class flares in NOAA 12673, revealing a double-decker flux rope configuration and complex plasma dynamics driven by tether-cutting reconnection and torus instability.

Contribution

It uncovers the presence of a compact double-decker flux rope in a mini-sigmoid and links it to the eruption mechanism using multiwavelength data and magnetic field extrapolation.

Findings

Presence of a double-decker flux rope prior to flares

Open field lines indicating emerging coronal hole

Eruption driven by tether-cutting reconnection and torus instability

Abstract

We present a multiwavelength analysis of two homologous, short lived, impulsive flares of GOES class M1.4 and M7.3, that occurred from a very localized mini-sigmoid region within the active region NOAA 12673 on 2017 September 7. Both flares were associated with initial jet-like plasma ejection which for a brief amount of time moved toward east in a collimated manner before drastically changing direction toward southwest. Non-linear force-free field extrapolation reveals the presence of a compact double-decker flux rope configuration in the mini-sigmoid region prior to the flares. A set of open field lines originating near the active region which were most likely responsible for the anomalous dynamics of the erupted plasma, gave the earliest indication of an emerging coronal hole near the active region. The horizontal field distribution suggests a rapid decay of the field above the active region, implying high proneness of the flux rope system toward eruption. In view of the low coronal double-decker flux ropes and compact extreme ultra-violet (EUV) brightening beneath the filament along with associated photospheric magnetic field changes, our analysis supports the combination of initial tether-cutting reconnection and subsequent torus instability for driving the eruption.