Quasi-periodic pulsations with double periods observed in Lyα emission during solar flares

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Quasi-periodic pulsations (QPPs) are very common oscillation features during solar flares,which have been observed in almost the entire wavelengths.However,the flare-related QPPs with double periods in the Lyα emission,particularly within a period ratio of about 2,were rarely detected.In this paper,we report the QPPs with double periods in the full-disk Lyα emission during the impulsive phase of four solar flares,i.e.,SOL2016-Feb-12,SOL2014-Oct-24,SOL2014-Jun-10,and SOL2012-Nov-21.The full-disk Lyα fluxes were recorded by the extreme-ultraviolet sensor on board the Geostationary Operational Environmental Satellite.Then,the quasi-periods are estimated by the Markov chain Monte Carlo (MCMC) sampling techniques.Finally,the double periods of around 3 and 1.5 min are detected in Lyα emissions,and their period ratio is roughly equal to 2.The 3-min QPP could also be detected in the local light curves measured by the Atmospheric Imaging Assembly at wavelengths of 304 and 1600 ~.Our observations suggest that the double periodic QPPs could be regarded as the fundamental and harmonic modes of acoustic waves,which should be helpful to understand magnetohydrodynamic waves in the solar chromosphere.However,we cannot rule out that the double periods are each caused by a different generation mechanism.
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