Hard X-Ray Quasiperiodic Pulsations in X-class Solar Flares Observed by Aditya-L1/HEL1OS

Abstract We present the catalogue of quasiperiodic pulsations (QPPs) detected in hard X-ray (HXR) observations of X-class solar flares obtained with the High Energy L1 Orbiting X-ray Spectrometer (HEL1OS) instrument on board Aditya-L1 during 2024 July–2026 March. The catalogue comprises 34 flares spanning GOES classes X1.1–X7.1. QPPs are detected and studied using a uniform procedure based on ensemble empirical mode decomposition (EEMD) and wavelet analyses. Statistically significant QPPs are identified in 25 events (∼74%), demonstrating that QPPs are a common property of X-class flares. The detected periods range from approximately 1 to 3 minutes, with a pronounced concentration between 1.3 and 1.7 minutes, suggesting the existence of a preferential timescale that may be associated with kink or slow magnetohydrodynamic oscillations in the flaring region. The dominant periods remain nearly independent of photon energy across the 8–20 keV range, while the modulation depth increases systematically with photon energy following a power-law relation with an exponent of about 1.5. QPPs detected in different HXR energy channels exhibit strong phase coherence and positive cross-correlation coefficients, indicating modulation by a common physical mechanism. Several intense flares display HXR modulation depths of up to ∼25%, providing evidence for nonlinear effects. The observed statistical properties support models in which QPPs are generated by repetitive magnetic reconnection, either spontaneous or periodically modulated by magnetohydrodynamic oscillations. This study establishes HEL1OS as a powerful instrument for quantitative studies of flare QPPs during solar cycle 25.