Magnetic reconnection: a common origin for flares and AR interconnecting arcs

Abstract

Abstract. Wepresentastudyofactiveregion(AR)7031,whereseveral flares occurred throughout the last week of January,1992. We analyze in detail the three largest flares, both in H αand soft X-rays. During its transit across the disk this regioninteracted with another one (AR 7038), as indicated by the re-current brightening in soft X-rays of an interconnecting loop,accompanied by sympathetic flaring.Using a linear force free extrapolation of the photosphericmagnetic field, we compute the locations of Quasi-SeparatrixLayers (QSLs), which are the likely places where the magneticfieldcanreconnect.Wefindthatflarebrighteningscanbelinkedby field lines having footpoints at the QSLs. Furthermore,field lines connecting AR 7031 and AR 7038 belong to theQSLs computed when magnetograms from both ARs arecombined. We conclude that both soft X-ray flare loops andinterconnecting loops result from magnetic reconnection at theQSLs. Which of the many QSLs found in the computationsare the site of magnetic reconnection depends on the magneticfield evolution. In the studied ARs we can identify threedifferent drivers for energy release: flux emergence, photo-spheric displacements of the polarities and nearby magneticreconnection. This last process leads to sympathetic flaring andto the brightness enhancement of the interconnecting arc.Key words: methods: data analysis – Sun: flares – Sun:magnetic fields1. IntroductionThe old debate about how many loops are involved in a flareappears to have no end. The main reason is because there areroughly as many observed flaring configurations in soft X-rayshaving one loop as having a multiple loop structure. After thefirst results from the Soft X-ray Telescope (SXT, Tsuneta et al.1991) the configuration with one single loop and two footpointsin soft X-rays became more popular (Dennis et al. 1994), but atthe same time the evidence for flares with interacting multiple