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We investigate the formation, activation and eruption of a flux rope from thesigmoid active region NOAA 11719 by analyzing E(UV), X-ray and radiomeasurements. During the pre-eruption period of ~7 hours, the AIA 94 A imagesreveal the emergence of a coronal sigmoid through the interaction between twoJ-shaped bundles of loops which proceeds with multiple episodes of coronal loopbrightenings and significant variations in the magnetic flux through thephotosphere. These observations imply that repetitive magnetic reconnectionslikely play a key role in the formation of the sigmoidal flux rope in thecorona and also contribute toward sustaining the temperature of the flux ropehigher than the ambient coronal structures. Notably, the formation of thesigmoid is associated with the fast morphological evolution of an S-shapedfilament channel in the chromosphere. The sigmoid activates toward eruptionwith the ascend of a large flux rope in the corona which is preceded by thedecrease of photospheric magnetic flux through the core flaring regionsuggesting tether-cutting reconnection as a possible triggering mechanism. Theflux rope eruption results in a two-ribbon M6.5 flare with a prolonged risephase of ~21 min. The flare exhibits significant deviation from the standardflare model in the early rise phase during which a pair of J-shaped flareribbons form and apparently exhibit converging motions parallel to the polarityinversion line which is further confirmed by the motions of HXR footpointsources. In the later stages, the flare follows the standard flare model andthe source region undergoes a complete sigmoid-to-arcade transformation.

Formation and eruption of a flux rope from the sigmoid active region NOAA 11719 and associated M6.5 flare: A multi-wavelength study