Slipping reconnection in a solar flare observed in high resolution with the GREGOR solar telescope

M Sobotka,J Staude,O Von Der Lühe,Dirk Schmidt ,R Schlichenmaier,M Sigwarth,Axel Hofmann ,C Denker,Thomas Berkefeld ,R Volkmer,J Jurčák,F Kneer,K G Strassmeier,M Collados ,C Kuckein,Wolfgang Schmidt ,A Lagg,H Nicklas,J Dudík,S K Solanki,D Soltau,A Feller,W.j Liu ,Rohan E Louis ,H Balthasar,T Waldmann

doi:10.1051/0004-6361/201527966

Abstract

A small flare ribbon above a sunspot umbra in active region 12205 was observed on November 7, 2014, at 12:00 UT in the blue imaging channel of the 1.5 m GREGOR telescope, using a 1 A Ca II H interference filter. Context observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical Telescope (SOT) onboard Hinode, and the Interface Region Imaging Spectrograph (IRIS) show that this ribbon is part of a larger one that extends through the neighboring positive polarities and also participates in several other flares within the active region. We reconstructed a time series of 140 seconds of Ca II H images by means of the multiframe blind deconvolution method, which resulted in spatial and temporal resolutions of 0.1 arcsec and 1 s. Light curves and horizontal velocities of small-scale bright knots in the observed flare ribbon were measured. Some knots are stationary, but three move along the ribbon with speeds of 7-11 km/s. Two of them move in the opposite direction and exhibit highly correlated intensity changes, which provides evidence of a slipping reconnection at small spatial scales.

Highlights

Solar flares are explosive phenomena that are characterized by a strong, rapid increase of electromagnetic radiation throughout the spectrum (e.g., Fletcher et al 2011)
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical Telescope (SOT) onboard Hinode, and the Interface Region Imaging Spectrograph (IRIS) show that this ribbon is part of a larger one that extends through the neighboring positive polarities and participates in several other flares within the active region
We presented GREGOR observations of slipping bright knots in a small ribbon-like structure within a sunspot umbra

Summary

Introduction

Solar flares are explosive phenomena that are characterized by a strong, rapid increase of electromagnetic radiation throughout the spectrum (e.g., Fletcher et al 2011). The magnetic reconnection in the QSLs is characterized by the apparent slipping motions of the field lines This occurs because of the continuous exchange of connectivities between reconnecting flux systems (Priest & Démoulin 1995; Priest et al 2003; Aulanier et al 2006, 2012; Janvier et al 2013). Li & Zhang (2015) found quasi-periodic patterns in small-scale bright knots that moved along the ribbon observed by the Interface Region Imaging Spectrograph spacecraft (IRIS, De Pontieu et al 2014) These observations of the slipping reconnection verify the predictions of the generalized 3D reconnection models (Aulanier et al 2006, 2012; Janvier et al 2013) and signify that the energy release in solar flares is an intrinsically 3D phenomenon.

Multiwavelength context observations

Slipping knots observed by GREGOR

Interpretation and discussion

Concluding remarks