Triggering Mechanism for Eruption of Two Filaments Observed by the Solar Dynamics Observatory, Nobeyama Radioheliograph, and RHESSI

We investigate the eruptive process of two filaments, which is associated with an M-class flare that occurred in 2011 August 4. The filaments are partly overlapped, one in the active region and the other just beside it, and erupt together as a halo coronal mass ejection. For this study, we used the Atmospheric Imaging Assembly and the Heliospheric Magnetic Imager on board the Solar Dynamics Observatory, the Nobeyama Radioheliograph 17 GHz, and the RHESSI Hard X-ray satellite. We found three distinct phases in the microwave flux profile and in the rising pattern of the filaments during the event. In the first phase, there was weak nonthermal emission at 17 GHz and hard X-rays. Those nonthermal sources appeared on one edge of the western filament (F2) in the active region. The F2 began to be bright and rose upward rapidly, while the eastern filament (F1), which was extended to the quiet region, started to brighten from the peak time of the 17 GHz flux. In the second phase, the nonthermal emission weakened and the F2 rose up slowly, while the F1 began to rise up. In the third phase, two filaments erupted together. Since the F1 was stable for a long time in the quiet region, breaking the equilibrium state of the F1 would be decisive for the successful eruption of two filaments and it seems clear that the evolution of the F2 provoked the unstable F1. We suggest that tether-cutting reconnection between two overlapped filaments triggers the eruption of the two filaments as a tangled identity.