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Fig. 3.


Helioseismic analysis snapshots of both full-angle (panel a) and directional 6 mHz egression power (panel b) at the time of quake onset (22:18:37 UT) highlights the presence of a detected acoustic kernel within statistical detection contour for the 6 mHz frequency band. We see acoustic emission to be reduced within the sunspot (penumbral boundary represented with white dashed contour), where magnetic fields damp stochastic effects. Directional egression computed with a displayed pupil arc highlights the acoustic kernel centred at 284″ × 129″. Value of the egression directional power is calculated at the location 284″ × 129″ and normalised to the local nonflaring levels is given in panel c, where angle denotes the starting angle of a 60° arc progressing anti-clockwise. TD diagram (panel d), is presented for the source centred at 284″×129″using arc of 0°−90°. A distance is in Mm and time is given in minutes starting at 22:11:07 UT. Fitting of the theoretical curve (right – black curve) yields an onset time of +7.5 min, or 22:18:37 UT.

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