Origin of extreme solar eruptive activity from the active region NOAA 12673 and the largest flare of solar cycle 24

TL;DR

This study analyzes the complex magnetic structures and evolution of active region NOAA 12673, which produced the largest flare of solar cycle 24, using multi-wavelength imaging and magnetic field modeling to understand its eruptive behavior.

Contribution

It provides a detailed multi-wavelength and magnetic field analysis of AR 12673, revealing the magnetic configurations associated with its extreme eruptive activity and the largest flare of cycle 24.

Findings

AR 12673 had highly complex magnetic fields leading to multiple powerful flares.

The largest flare (X9.3) was associated with specific magnetic configurations and evolution.

Magnetic field structures played a key role in triggering the eruptions.

Abstract

During 2017, when the Sun was moving toward the minimum phase of solar cycle 24, an exceptionally eruptive active region (AR) NOAA 12673 emerged on the Sun during August 28-September 10. During the highest activity level, the AR turned into a delta-type sunspot region, which manifests the most complex configuration of magnetic fields from the photosphere to the coronal heights. The AR 12673 produced four X-class and 27 M-class flares, along with numerous C-class flares, making it one of the most powerful ARs of solar cycle 24. Notably, it produced the largest flare of solar cycle 24, namely, the X9.3 event on 2017 September 6. In this work, we highlight the results of our comprehensive analysis involving multi-wavelength imaging and coronal magnetic field modeling to understand the evolution and eruptivity from AR 12673. We especially focus on the morphological, spectral and kinematical evolution of the two X-class flares on 6 September 2017. We explore various large- and small-scale magnetic field structures of the active region which are associated with the triggering and subsequent outbursts during the powerful solar transients.