Large-amplitude Longitudinal Oscillations Triggered by the Merging of Two Solar Filaments: Observations and Magnetic Field Analysis

We follow the eruption of two related intermediate filaments observed in Ha (from GONG) and EUV (from Solar Dynamics Observatory SDO/Atmospheric Imaging assembly AIA) and the resulting large-amplitude longitudinal oscillations of the plasma in the filament channels. The events occurred in and around the decayed active region AR12486 on 2016 January 26. Our detailed study of the oscillation reveals that the periods of the oscillations are about one hour. In H alpha, the period decreases with time and exhibits strong damping. The analysis of 171 angstrom images shows that the oscillation has two phases: an initial long-period phase and a subsequent oscillation with a shorter period. In this wavelength, the damping appears weaker than in Ha. The velocity is the largest ever detected in a prominence oscillation, approximately 100 km s(-1). Using SDO/HMI magnetograms, we reconstruct the magnetic field of the filaments, modeled as flux ropes by using a flux-rope insertion method. Applying seismological techniques, we determine that the radii of curvature of the field lines in which cool plasma is condensed are in the range 75-120. Mm, in agreement with the reconstructed field. In addition, we infer a field strength of >= 7 to 30 Gauss, depending on the electron density assumed, that is also in agreement with the values from the reconstruction (8-20 Gauss). The poloidal flux is zero and the axis flux is on the order of 10(20) to 10(21) Mx, confirming the high shear existing even in a non-active filament.