(a) Observation of a sigmoidal loop (marked by the white dashed curve) associated with the pre-eruptive structure as seen in the AIA 171 Å channel. (b) Base difference image obtained from the AIA 193 Å channel. Green circles mark the two conjugate core-dimming regions observed during the eruption. (c) Line-of-sight component of the HMI magnetic field. The yellow dashed curve and the green circles are drawn in (a) and (b), respectively. The underlying magnetic polarities of the two conjugate core-dimming regions and the two ends of the sigmoidal loop are marked, indicating a northeast-directed left-handed flux rope.