Very Long-periodic Pulsations Detected Simultaneously in a White-light Flare and Sunspot Penumbra

We investigate the origin of very long-periodic pulsations in the white-light emission of an X6.4 flare on 2024 February 22 (SOL2024-02-22T22:08), which occurred at the edge of a sunspot group. The flare white-light fluxes reveal four successive and repetitive pulsations, which are simultaneously measured by the Helioseismic and Magnetic Imager and the White-light Solar Telescope. A quasi-period of minutes, determined by the Morlet wavelet transform, is detected in the visible continuum channel. The modulation depth, which is defined as the ratio between the oscillatory amplitude and its long-term trend, is smaller than 0.1%, implying that the quasi-periodic pulsation (QPP) feature is a weak wave process. Imaging observations show that the X6.4 flare occurs near a sunspot group. Moreover, the white-light brightening is located in sunspot penumbra, and a similar quasi-period of about 8.5 minutes is identified in one penumbral location of the nearest sunspot. The map of Fourier power distribution suggests that a similar periodicity is universally existing in most parts of the penumbra that is close to the penumbral–photospheric boundary. Our observations support the scenario that the white-light QPP is probably modulated by the slow-mode magnetoacoustic gravity wave leaking from the sunspot penumbra.