Astronomy and Astrophysics
Aims: We present two different case studies as observational evidence in support of 2.5D numerical magnetohydrodynamics (MHD) experiments that show that the LAOs in the filament channels can be initiated by solar jets.
Methods: We use longitudinal magnetic field observations using the Helioseismic Magnetic Imager to study the evolution of the filament channels. The LAOs in the filaments are analysed using two techniques. The first is time-distance diagnostics with extreme-ultraviolet (EUV) and Hα datasets. In the second method, the oscillations in different parts of the filaments are examined using Fourier analysis of the brightness variations of all pixels in Hα observations.
Results: In the two studied events, we can identify a quadrupolar configuration with an X-point at the top of the parasitic region suggestive of a classical null-point. The X-point evolves into a flat structure suggestive of a breakout current sheet. A reconnection flow emanates from this structure, leading to a jet that propagates along the filament channel. In both cases, we can identify the quiescent and eruptive phases of the jet. The triggered LAOs have periods of around 70-80 min and are damped after a few oscillations. The minimum magnetic field intensity inferred with seismology for the filament turns out to be around 30 Gauss.
Conclusions: We conclude that the two case studies are consistent with a recently published numerical model in which the LAOs are initiated by jets. The relationship between the onset of the jet and filament oscillations is straightforward for the first case but is less clear for the second case. In the second event, although there is some evidence for a relationship, we cannot rule out other possibilities such as activity unrelated to the null-point or changes in the magnetic structure of the filament. Both jets are associated with very weak flares that did not launch any EUV waves. Therefore, a role of EUV waves in triggering the filament oscillations can be eliminated for these two cases. Movies associated to Figs. 3 and 13 are available at https://www.aanda.org