Quasi-periodic pulsations and three-dimensional magnetic reconnection during 2022 March 31 flare observed by IRIS & STIX

TL;DR

This study analyzes high-cadence IRIS and STIX observations of a 2022 solar flare, revealing correlations between UV and HXR pulsations, and providing new insights into 3D magnetic reconnection processes.

Contribution

It links UV and HXR quasi-periodic pulsations to slipping reconnection and 3D magnetic structures using multi-instrument data and NLFFF extrapolation.

Findings

HXR QPPs with ~35 s period detected at two footpoints.

UV pulsations correlated with HXR QPPs in ribbon regions.

Slipping kernels showed weaker energization, constraining 3D reconnection models.

Abstract

Apparent slipping motions of flare ribbon kernels and the formation of hard X-ray (HXR) footpoints are important signatures of magnetic reconnection in solar flares. Ultraviolet (UV) and HXR ribbon emission can show quasi-periodic pulsations (QPPs), but the link between HXR QPP sources and slipping reconnection remains poorly understood. In this work, we analyze high-cadence IRIS and STIX observations of the 2022 March 31 M9.6 flare. STIX detected non-thermal QPPs with periods of $\approx$35 s from two relatively stationary footpoints. The majority of the HXR QPPs were correlated with UV pulsations observed by the IRIS Slit Jaw Imager in ribbon regions encompassing these footpoints. In one such region observed under the IRIS slit, the Si IV 1402.77{\AA} line exhibited pulsations in intensity, Doppler shift, and width, some of which were coincident with HXR QPPs. Apparent slipping motions of the UV kernels were also observed, but their locations, timing, and UV intensity variability showed lower correlation with the HXR QPPs. The ribbons along which the slipping kernels were found correspond well to footprints of quasi-separatrix layers (QSLs), regions of high magnetic connectivity gradients, identified using a NLFFF extrapolation. Our multi-instrument analysis suggests that strong deposition of energy by non-thermal electrons was concentrated in a specific loop system within a large-scale 3D reconnection structure. Slipping kernels were subjected to weaker, if any, energization by non-thermal electrons, offering new constraints on 3D reconnection and flare energy release.