Properties of the 15 February 2011 Flare Seismic Sources
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The first near-side X-class flare of Solar Cycle 24 occurred in February 2011 (SOL2011-02-05T01:55) and produced a very strong seismic response in the photosphere. One sunquake was reported by Kosovichev (Astrophys. J. Lett. 734, L15, 2011), followed by the discovery of a second sunquake by Zharkov, Green, Matthews et al. (Astrophys. J. Lett. 741, L35, 2011). The flare had a two-ribbon structure and was associated with a flux-rope eruption and a halo coronal mass ejection (CME) as reported in the CACTus catalogue. Following the discovery of the second sunquake and the spatial association of both sources with the locations of the feet of the erupting flux rope (Zharkov, Green, Matthews et al., Astrophys. J. Lett. 741, L35, 2011), we present here a more detailed analysis of the observed photospheric changes in and around the seismic sources. These sunquakes are quite unusual, taking place early in the impulsive stage of the flare, with the seismic sources showing little hard X-ray (HXR) emission, and strongest X-ray emission sources located in the flare ribbons. We present a directional time–distance diagram computed for the second source, which clearly shows a ridge corresponding to the travelling acoustic-wave packet and find that the sunquake at the second source happened about 45 seconds to one minute earlier than the first source. Using acoustic holography we report different frequency responses of the two sources. We find strong downflows at both seismic locations and a supersonic horizontal motion at the second site of acoustic-wave excitation.
KeywordsSun: helioseismology Sun: flares Sun: X-rays Gamma ray
Solar Dynamics Observatory
Helioseismic and Magnetic Imager
Atmospheric Imaging Assembly
The authors thank C. Lindsey for his help in obtaining acoustic-energy estimates. The authors also thank the anonymous referee for their insightful comments. We acknowledge the Leverhulme Trust for funding the “Probing the Sun: inside and out” project upon which this research is based. We acknowledge use of SDO/HMI data, courtesy of NASA/SDO and the HMI science team, data courtesy of Hinode, a Japanese mission developed and launched by ISAS/JAXA in partnership with NAOJ and in collaboration with NASA (USA) and STFC (UK), and operated by these agencies in co-operation with ESA and NSC (Norway), and the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), a NASA small explorer mission.
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