Quasiperiodic Oscillations of Flare Loops and Slipping Motion of Ribbon Substructures during a C-class Flare

Quasiperiodic oscillations in solar-flaring emission have been observed over the past few decades. To date, the underpinning processes resulting in the quasiperiodic oscillations remain unknown. In this paper, we report a unique event that exhibits both the long-duration quasiperiodic intensity oscillations of flare loops and the quasiperiodic slipping motion of ribbon substructures during a C9.1-class flare (SOL2015-03-15-T01:15), using the observations from the Solar Dynamics Observatory and Interface Region Imaging Spectrograph. The high-temperature flare loops rooted in the straight part of ribbons display a "bright-dim" intensity oscillation, with a period of about 4.5 minutes. The oscillation starts just after the flare onset and lasts over 3 hr. Meanwhile, the substructures within the ribbon tip display the quasiperiodic slipping motion along the ribbon at 1400 & Aring; images, which has a similar periodicity to the stationary intensity oscillation of the flare loops in the straight part of the flare ribbons. We suggest that the quasiperiodic pattern is probably related to the loop-top dynamics caused by the reconnection outflow impinging on the flare loops.