Onset of Photospheric Impacts and Helioseismic Waves in X9.3 Solar Flare of September 6, 2017

TL;DR

This study analyzes the photospheric impacts and helioseismic waves generated by the powerful X9.3 solar flare of September 6, 2017, revealing localized pre-impulsive phase impacts and identifying sources of sunquakes linked to magnetic structures.

Contribution

It provides new insights into the spatio-temporal dynamics of flare impacts and helioseismic wave sources, emphasizing the role of magnetic structures and pre-impulsive phase activity.

Findings

Photospheric impacts began before HXR detection near the PIL.

Two primary sources of sunquakes linked to strong impacts.

Sequential involvement of sheared magnetic loops during energy release.

Abstract

The X9.3 flare of September 6, 2017, was the most powerful flare of Solar Cycle 24. It generated strong white-light emission and multiple helioseismic waves (sunquakes). By using data from Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) as well as hard X-ray data from KONUS instrument onboard WIND spacecraft, and Anti-Coincidence System (ACS) onboard the INTERGRAL space observatory, we investigate spatio-temporal dynamics of photospheric emission sources, identify sources of helioseismic waves and compare the flare photospheric dynamics with the hard X-ray (HXR) temporal profiles. The results show that the photospheric flare impacts started to develop in compact regions in close vicinity of the magnetic polarity inversion line (PIL) in the pre-impulsive phase before detection of the HXR emission. The initial photospheric disturbances were localized in the region of strong horizontal magnetic field of the PIL, and, thus, are likely associated with a compact sheared magnetic structure elongated along the PIL. The acoustic egression power maps revealed two primary sources of generation of sunquakes, which were associated with places of the strongest photospheric impacts in the pre-impulsive phase and the early impulsive phase. This can explain the two types of helioseismic waves observed in this flare. Analysis of the high-cadence HMI filtergrams suggests that the flare energy release developed in the form of sequential involvement of compact low-lying magnetic loops that were sheared along the PIL.