Preflare Processes, Flux Rope Activation, Large-scale Eruption, and Associated X-class Flare from the Active Region NOAA 11875

Abstract

Abstract We present a multiwavelength analysis of the eruption of a hot coronal channel associated with an X1.0 flare (SOL2013-10-28T02:03) from the active region NOAA 11875 by combining observations from Atmospheric Imaging Assembly/Solar Dynamics Observatory (SDO), Helioseismic and Magnetic Imager/SDO, Reuven Ramaty High Energy Solar Spectroscopic Imager, and Hiraiso Radio Spectrograph. EUV images at high coronal temperatures indicated the presence of a hot channel at the core of the active region from the early preflare phase evidencing the preexistence of a quasi-stable magnetic flux rope. The hot channel underwent an activation phase after a localized and prolonged preflare event occurring adjacent to one of its footpoints. Subsequently, the flux rope continued to rise slowly for ≈16 minutes during which soft X-ray flux gradually built-up characterizing a distinct precursor phase. The flux rope transitioned from the state of slow rise to the eruptive motion with the onset of the impulsive phase of the X1.0 flare. The eruptive expansion of the hot channel is accompanied by a series of type III radio bursts in association with the impulsive rise of strong hard X-ray nonthermal emissions that included explicit hard X-ray sources of energies up to ≈50 keV from the coronal loops and ≈100 keV from their footpoint locations. Our study contains evidence that preflare activity occurring within the spatial extent of a stable flux rope can destabilize it toward eruption. Moreover, sudden transition of the flux rope from the state of slow rise to fast acceleration precisely bifurcated the precursor and the impulsive phases of the flare, which points toward a feedback relationship between early coronal mass ejection dynamics and the strength of the large-scale magnetic reconnection.