Triggering of the 2024 August 8 X1.3 Flare by Peripheral Flux Emergence

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Abstract We investigate an X1.3 flare in active region 13777 on 2024 August 8, which was preceded by precursor brightening associated with small-scale magnetic flux emergence and cancellation at the periphery of the leading polarity. Multi-instrument observations from Solar Dynamics Observatory/Helioseismic and Magnetic Imager, Atmospheric Imaging Assembly, ground-based GONG H α , and Goode Solar Telescope/Fast Imaging Solar Spectrograph show that the precursor did not immediately lead to the flare onset, but was followed by a gradual elongation and destabilization of a filament that connected the peripheral pore to the main sunspot. The flare developed first as a two-ribbon flare confined to the low-lying filament and later as a complex-ribbon flare accompanied by the removal of overlying arcades. κ -scheme analysis proposed by Kusano et al. revealed that the small region of high free-energy at the periphery had already become unstable to the double-arc instability at the time of the precursor brightening, although the large-scale eruption required further coupling with the main sunspot system. These results suggest that even a very small-scale flux emergence at the periphery of an active region can reorganize the magnetic system and eventually lead to a major flare.

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