Abstract
ApJL 852 (2018) 10 We describe the peculiarity of two recurrent white light flares occurred on
Sept. 06, 2017, in the super Active Region (SAR) NOAA 12673, with a time
interval, between their peaks, of about 3 hours. These events of X2.2 and X9.3
GOES class are very important not only for their high level of emission and for
the visible effects on the lower layers of the solar atmosphere, discernible as
clear white light ribbons, but as well for the strong horizontal photospheric
motions which seemed to drive them. In fact, we observed for several hours
before the flare occurrence the displacement of a negative umbra located in the
main delta spot of the Active Region. We measured velocities up to 0.6 km
s$^{-1}$. The strong and persistent shear motion of the photospheric structures
together with the high intensity of the magnetic flux involved by these events
can be considered responsible for the new energy continuously supplied into the
magnetic system. From the timing of the emissions at different wavelengths we
were able to provide some constraints for the modeling of such events.