  The X9.3 flare of September 6, 2017, was the most powerful flare of Solar
Cycle 24. It generated strong white-light emission and multiple helioseismic
waves (sunquakes). By using data from Helioseismic and Magnetic Imager (HMI)
onboard the Solar Dynamics Observatory (SDO) as well as hard X-ray data from
KONUS instrument onboard WIND spacecraft, and Anti-Coincidence System (ACS)
onboard the INTERGRAL space observatory, we investigate spatio-temporal
dynamics of photospheric emission sources, identify sources of helioseismic
waves and compare the flare photospheric dynamics with the hard X-ray (HXR)
temporal profiles. The results show that the photospheric flare impacts started
to develop in compact regions in close vicinity of the magnetic polarity
inversion line (PIL) in the pre-impulsive phase before detection of the HXR
emission. The initial photospheric disturbances were localized in the region of
strong horizontal magnetic field of the PIL, and, thus, are likely associated
with a compact sheared magnetic structure elongated along the PIL. The acoustic
egression power maps revealed two primary sources of generation of sunquakes,
which were associated with places of the strongest photospheric impacts in the
pre-impulsive phase and the early impulsive phase. This can explain the two
types of helioseismic waves observed in this flare. Analysis of the
high-cadence HMI filtergrams suggests that the flare energy release developed
in the form of sequential involvement of compact low-lying magnetic loops that
were sheared along the PIL.

Solar and Stellar Astrophysics