Hα spectroscopy and multiwavelength imaging of a solar flare caused by filament eruption ^⋆

¹ Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Shandong University (Weihai), 264209 Weihai, Shandong, PR China
e-mail: zhu@arm.ac.uk
² Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
³ Institute of Astronomy and National Astronomical Observatory, BAS, 72 Tsarigradsko Chaussee blvd., 1784 Sofia, Bulgaria
⁴ National Solar Observatory, Sacramento Peak, PO Box 62, Sunspot, NM 88349, USA

Received: 21 November 2013
Accepted: 6 May 2014

Abstract

Context. We study a sequence of eruptive events including filament eruption, a GOES C4.3 flare, and a coronal mass ejection.

Aims. We aim to identify the possible trigger(s) and precursor(s) of the filament destabilisation, investigate flare kernel characteristics, flare ribbons/kernels formation and evolution, study the interrelation of the filament-eruption/flare/coronal-mass-ejection phenomena as part of the integral active-region magnetic field configuration, and determine Hα line profile evolution during the eruptive phenomena.

Methods. Multi-instrument observations are analysed including Hα line profiles, speckle images at Hα – 0.8 Å and Hα + 0.8 Å from IBIS at DST/NSO, EUV images and magnetograms from the SDO, coronagraph images from STEREO, and the X-ray flux observations from Fermi and GOES.

Results. We establish that the filament destabilisation and eruption are the main triggers for the flaring activity. A surge-like event with a circular ribbon in one of the filament footpoints is determined as the possible trigger of the filament destabilisation. Plasma draining in this footpoint is identified as the precursor for the filament eruption. A magnetic flux emergence prior to the filament destabilisation followed by a high rate of flux cancellation of 1.34 × 10¹⁶ Mx s^-1 is found during the flare activity. The flare X-ray lightcurves reveal three phases that are found to be associated with three different ribbons occurring consecutively. A kernel from each ribbon is selected and analysed. The kernel lightcurves and Hα line profiles reveal that the emission increase in the line centre is stronger than that in the line wings. A delay of around 5–6 min is found between the increase in the line centre and the occurrence of red asymmetry. Only red asymmetry is observed in the ribbons during the impulsive phases. Blue asymmetry is only associated with the dynamic filament.