The 6 September 2017 X9 Super Flare Observed From Submillimeter to Mid-IR

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Space Weather
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Gimenez de Castro C.G.
Raulin J.-P.
Valle Silva J.F.
Simoes P.J.A.
Kudaka A.S.
Valio A.
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©2018. American Geophysical Union. All Rights Reserved.Active Region 12673 is the most productive active region of solar cycle 24: in a few days of early September 2017, four X-class and 27 M-class flares occurred. SOL2017-09-06T12:00, an X9.3 flare also produced a two-ribbon white light emission across the sunspot detected by Solar Dynamics Orbiter/Helioseismic and Magnetic Imager. The flare was observed at 212 and 405 GHz with the arcminute-sized beams of the Solar Submillimeter Telescope focal array while making a solar map and at 10 μm, with a 17 arcsec diffraction-limited infrared camera. Images at 10 μm revealed that the sunspot gradually increased in brightness while the event proceeded, reaching a temperature similar to quiet Sun values. From the images we derive a lower bound limit of 180-K flare peak excess brightness temperature or 7,000 sfu if we consider a similar size as the white light source. The rising phase of mid-IR and white light is similar, although the latter decays faster, and the maximum of the mid-IR and white light emission is ∼200 s delayed from the 15.4-GHz peak occurrence. The submillimeter spectrum has a different origin than that of microwaves from 1 to 15 GHz, although it is not possible to draw a definitive conclusion about its emitting mechanism.
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