The Chromospheric Response to the Sunquake generated by the X9.3 Flare of NOAA 12673

Abstract

Active region NOAA 12673 was extremely volatile in 2017 September, producing many solar flares, including the largest of solar cycle 24, an X9.3 flare of 06 September 2017. It has been reported that this flare produced a number of sunquakes along the flare ribbon (Sharykin & Kosovichev 2018; Zhao & Chen 2018). We have used co-temporal and co-spatial Helioseismic and Magnetic Imager (HMI) line-of-sight (LOS) and Swedish 1-m Solar Telescope observations to show evidence of the chromospheric response to these sunquakes. Analysis of the Ca II 8542 Å\space line profiles of the wavefronts revealed that the crests produced a strong blue asymmetry, whereas the troughs produced at most a very slight red asymmetry. We used the combined HMI, SST datasets to create time-distance diagrams and derive the apparent transverse velocity and acceleration of the response. These velocities ranged from 4.5 km s${}^{-1}$ to 29.5 km s${}^{-1}$ with a constant acceleration of 8.6 x 10${}^{-3}$ km s${}^{-2}$. We employed NICOLE inversions, in addition to the Center-of-Gravity (COG) method to derive LOS velocities ranging 2.4 km s${}^{-1}$ to 3.2 km s${}^{-1}$. Both techniques show that the crests are created by upflows. We believe that this is the first chromospheric signature of a flare induced sunquake.

arXiv comment11 Pages, 6 Figures

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• Synthesizing Sun-as-a-star flare spectra from high-resolution solar observations
• Physical properties of a fan-shaped jet backlit by an X9.3 flare
• A Possible Selection Rule for Flares Causing Sunquakes
• The effect of a solar flare on chromospheric oscillations
• Flare Induced Sunquake Signatures in the Ultraviolet as Observed by the Atmospheric Imaging Assembly