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In this article, we study the origin of precursor flare activity andinvestigate its role towards triggering the eruption of a flux rope whichresulted into a dual-peak M-class flare (SOL2015-06-21T02:36) in the activeregion NOAA 12371. The flare evolved in two distinct phases with peak fluxlevels of M2.1 and M2.6 at an interval of $\approx$54 min. The active regionexhibited striking moving magnetic features (MMFs) along with sunspot rotation.Non-linear force free field (NLFFF) modelling of the active region coronareveals a magnetic flux rope along the polarity inversion line in the trailingsunspot group which is observationally manifested by the co-spatial structuresof an active region filament and a hot channel identified in the 304 and 94\AA\ images, respectively, from the Atmospheric Imaging Assembly (AIA). Theactive region underwent a prolonged phase of flux enhancement followed by arelatively shorter period of flux cancellation prior to the onset of the flarewhich led to the build up and activation of the flux rope. Extreme ultra-violet(EUV) images reveal localised and structured pre-flare emission, from theregion of MMFs, adjacent to the location of the main flare. Our analysisreveals strong, localised regions of photospheric currents of oppositepolarities at the precursor location, thereby making the region susceptible tosmall-scale magnetic reconnection. Precursor reconnection activity from thislocation most likely induced a slipping reconnetion towards the northern leg ofthe hot channel which led to the destabilization of the flux rope. Theapplication of magnetic virial theorem suggests that there was an overallgrowth of magnetic free energy in the active region during the prolongedpre-flare phase which decayed rapidly after the hot channel eruption and itssuccessful transformation into a halo coronal mass ejection (CME).

solar physics

Identification of Pre-flare Processes and Their Possible Role in Driving  a Large-scale Flux Rope Eruption with Complex M-class Flare in the Active  Region NOAA 12371