Quasiperiodic Slipping Motion of Flare Ribbon Fine Structures Anchored in a Sunspot Light Bridge

TL;DR

This study reveals that fine structures called 'burrs' in a solar flare ribbon exhibit quasiperiodic slipping motions, linked to magnetic reconnection processes modulated by p-mode oscillations, providing insights into flare energy release mechanisms.

Contribution

The paper presents high-resolution observations of flare ribbon substructures, demonstrating their systematic slipping motions and periodicity, and links these to magnetic reconnection modulated by p-mode oscillations.

Findings

Burrs are discrete substructures with specific size and motion characteristics.

Burrs exhibit a ~6-minute quasi-periodicity in their slipping motion.

The observed features are consistent with impulsive energy deposition by tearing-mode fragmentation.

Abstract

We used high-resolution observations from the New Vacuum Solar Telescope and the Solar Dynamics Observatory to carry out a detailed multiwavelength analysis of the fine structures in the flare ribbon of a C3.9-class flare on 22 April 2021. A segment of the flare ribbon was rooted in a sunspot light bridge and exhibited discrete substructures, which we term "burrs", with equivalent diameters of 233-895 km and inter-core separations of 1129-1739 km. These structures are characterized by discrete redshifted cores accompanied by "tails" with lengths of 700-1370 km and widths of 310-600 km that show faint blueshifts. The burrs display systematic slipping motions along the ribbon, with apparent velocities decreasing from about 40 to 21 km/s, and show a distinct quasi-periodicity of about 6 minutes in H-alpha and EUV passbands. Differential emission measure analysis indicates that the emitting plasma is multi-thermal and dominated by temperatures of 1-2 MK. The observed morphology and kinematics are consistent with impulsive energy deposition by precipitating plasmoids, or oblique flux ropes, produced by tearing-mode fragmentation in the coronal current sheet. The close spatiotemporal association between the tails and blueshifts supports the interpretation that these features are related to untwisting magnetic flux ropes. The approximately 6-minute periodicity further suggests that the reconnection process may be modulated by photospheric p-mode oscillations coupled with tearing-mode instability. These results provide observational evidence that light-bridge-anchored fine structures can act as elementary units of flare energy release.