White-light Continuum Observation of the Off-limb Loops of the SOL2017-09-10 X8.2 Flare: Temporal and Spatial Variations

TL;DR

This study presents detailed observations of the off-limb white-light flare loops during the SOL2017-09-10 X8.2 event, revealing temporal and spatial variations and pulsations that inform flare energy release mechanisms.

Contribution

It provides the first comprehensive analysis of off-limb WL flare loops with multi-wavelength data, highlighting pulsation behaviors and flux evolution.

Findings

Detection of ~8-minute quasi-periodic pulsations in WL and UV emissions.

UV emissions occur earlier and higher than WL emissions in the flare loops.

WL flux continues to grow while UV flux decays, indicating complex emission mechanisms.

Abstract

Observations of the Sun's off-limb white-light (WL) flares offer rare opportunities to study the energy release and transport mechanisms in flare loops. One of the best such events was SOL2017-09-10, an X8.2 flare that occurred near the Sun's west limb on 2017 September 10 and produced a WL loop system lasting more than 60 minutes and reaching an altitude higher than 30 Mm. The event was well observed by a suite of ground- and space-based instruments, including the Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) that captured its off-limb loops in WL continuum near Fe I 6173 A, and the Atmospheric Imager Assembly (SDO/AIA) that observed its ultraviolet (UV) and extreme-ultraviolet (EUV) counterparts. We found quasi-periodic pulsations in the WL and UV emissions at the flare loop-top with a period around 8.0 min. Each pulsation appears to have an EUV counterpart that occurs earlier in time and higher in altitude. Despite many similarities in the WL and UV images and light curves, the WL flux at the loop-top continues to grow for about 16 minutes while the UV fluxes gradually decay. We discuss the implication of these unprecedented observations on the understanding of the enigmatic off-limb WL flare emission mechanisms.