Properties of the 15 February 2011 Flare Seismic Sources

TL;DR

This paper analyzes the properties and detailed photospheric changes of two unusual sunquakes triggered by the February 2011 X-class solar flare, highlighting their timing, acoustic responses, and associated magnetic activity.

Contribution

It provides a detailed analysis of two sunquake sources, including their timing, acoustic properties, and relation to flare dynamics, which was not previously documented in such detail.

Findings

Sunquakes occurred early in the flare's impulsive phase.

The second source's quake preceded the first by 45 seconds to one minute.

Different frequency responses were observed at the two seismic sources.

Abstract

The first near-side X-class flare of the Solar Cycle 24 occurred in February 2011 and produced a very strong seismic response in the photosphere. One sunquake was reported by Kosovichev (2011) followed by the discovery of a second sunquake by Zharkov et al (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 et al 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 quake 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.