Longitudinal filament oscillations enhanced by two C-class flares

Abstract

Context. Large-amplitude, longitudinal filament oscillations triggered by solar flares have been well established in the literature. However, filament oscillations enhanced by flares have never been reported. Aims. In this paper we report the multiwavelength observations of a very long filament in active region (AR) 11112 on 2010 October 18. The filament was composed of two parts, the eastern part (EP) and the western part (WP). We focus on longitudinal oscillations of the EP, which were enhanced by two homologous C-class flares in the same AR. Methods. The filament was observed in Hα wavelength by the Global Oscillation Network Group and in extreme ultraviolet wavelengths by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO). Line-of-sight magnetograms were provided by the Helioseismic and Magnetic Imager on board SDO. The global three-dimensional magnetic fields were obtained using the potential field source surface modeling. Soft X-ray light curves of the two flares were recorded by the GOES spacecraft. White light images of the corona were observed by the LASCO/C2 coronagraph on board SOHO. To reproduce part of the observations, we perform one-dimensional, hydrodynamic numerical simulations using the MPI-AMRVAC code. Results. The C1.3 flare was confined without a coronal mass ejection (CME). Both EP and WP of the filament were slightly disturbed and survived the flare. After 5 h, eruption of the WP generated a C2.6 flare and a narrow jet-like CME. Three oscillating threads (thda, thdb, thdc) are obviously identified in the EP, and their oscillations are naturally divided into three phases by the two flares. The initial amplitude ranges from 1.6 to 30 Mm with a mean value of ∼14 Mm. The period ranges from 34 to 73 min with a mean value of ∼53 min. The curvature radii of the magnetic dips are estimated to be 29 to 133 Mm with a mean value of ∼74 Mm. The damping times ranges from ∼62 to ∼96 min with a mean value of ∼82 min. The value of τ/P is between 1.2 and 1.8. For thda in the EP, the amplitudes were enhanced by the two flares from 6.1 Mm to 6.8 Mm after the C1.3 flare, and further to 21.4 Mm after the C2.6 flare. The period variation as a result of perturbation from the flares was within 20%. The attenuation became faster after the C2.6 flare. Conclusions. To the best of our knowledge, this is the first report of large-amplitude, longitudinal filament oscillations enhanced by flares. Numerical simulations reproduce the oscillations of thda very well. The simulated amplitudes and periods are close to the observed values, while the damping time in the last phase is longer, implying additional mechanisms should be taken into account apart from radiative loss.