Two-Stage Evolution of an Extended C-Class Eruptive Flaring Activity from Sigmoid Active Region NOAA 12734: SDO and Udaipur-CALLISTO Observations

In this article, we present a multi-wavelength investigation of a C-class flaring activity that occurred in the active region NOAA 12734 on 8 March 2019. The investigation utilizes data from the Atmospheric Imaging Assembly (AIA) and the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) and the Udaipur-CALLISTO solar radio spectrograph of the Physical Research Laboratory. This low intensity C1.3 event is characterized by typical features of a long-duration event (LDE), viz. extended flare arcade, large-scale two-ribbon structures and twin coronal dimmings. The eruptive event occurred in a coronal sigmoid and displayed two distinct stages of energy release, manifested in terms of temporal and spatial evolution. The formation of twin-dimming regions are consistent with the eruption of a large flux rope with footpoints lying in the western and eastern edges of the coronal sigmoid. The metric radio observations obtained from Udaipur-CALLISTO reveals a broad-band ( $\approx50\,\text{--}\,180~\text{MHz}$ ), stationary plasma emission for $\approx7~\text{min}$ during the second stage of the flaring activity that resemble a type IV radio burst. A type III decametre-hectometre radio bursts with starting frequency of $\approx2.5~\text{MHz}$ precedes the stationary type IV burst observed by Udaipur-CALLISTO by $\approx5~\text{min}$ . The synthesis of multi-wavelength observations and non-linear force-free field (NLFFF) coronal modeling together with magnetic decay index analysis suggest that the sigmoid flux rope underwent a zipping-like uprooting from its western to eastern footpoints in response to the overlying asymmetric magnetic field confinement. The asymmetrical eruption of the flux rope also accounts for the observed large-scale structures viz. apparent eastward shift of flare ribbons and post-flare loops along the polarity inversion line (PIL), and provides evidence for lateral progression of magnetic reconnection site as the eruption proceeds.