Multiwavelength Observations of Quasiperiodic Pulsations in the Impulsive Phase of an Eruptive Flare with the Hard X-Ray Imager On Board ASO-S and Other Instruments

We investigated the quasiperiodic pulsations (QPPs) of the X1.2 solar flare (SOL2023-01-06T00:57) based on multi-instrument observations, especially the Hard X-ray Imager (HXI) on board the Advanced Space-based Solar Observatory (ASO-S). The quasiperiod of ≈ 27 s was identified in hard X-rays (HXR) and microwaves using the Markov Chain Monte Carlo method, while no corresponding oscillation was found in soft X-rays. The HXI imaging demonstrates that HXR pulsations arise from the double-footpoint HXR sources. Moreover, the fluctuation of ≈ 27 s period was also present in the nonthermal electron power-law index derived from the X-ray spectra, which is the signature of periodic electron acceleration/precipitation during the impulsive phase. The electron spectral indices not only exhibited the well-known “soft–hard–soft” evolution, but also showed the negative correlation with the HXR pulsations. These results suggest that QPPs directly originate from quasiperiodic injections of accelerated electrons into flare-loop footpoints. We also discuss the possible generation mechanisms for QPPs.