High-resolution Observations of a Flare Associated with a Partial Filament Eruption on 2023 April 21

We investigate an eruptive M-class flare on 2023 April 21 (SOL2023-04-21T18:12) with observations from the Solar Dynamics Observatory and the Chinese Hα Solar Explorer. We discuss two stages of energy release, the preflare activity and the eruptive flare. The preflare phase features some brightening of the lower atmosphere, the rising motion of filament materials, and a brightening ribbon structure. We suggest that low-altitude magnetic reconnection triggers the eruptive activity. The reconnection between the ambient loops and continuously rising thread-like structures produced the well-formed parallel-ribbon flare. In the main flare phase, the filament experienced a partial eruption with significant plasma motion in the constrained part. We propose a double-decker filament structure based on the multiwavelength observations and analysis of the magnetic field.