Observation of the X9.3 flare of September 6 2017 in UV/EUV by PROBA2/LYRA
Abstract
After several months of relative quietness, a sudden burst of solar activity was observed starting on September 4 2017, when the NOAA AR 12673 started to develop quickly. This region remained active until it disappeared behind the west limb on September 10. It produced multiple strong flares (27 M-class flares and 4 X-class flares). Among them, there were the two strongest flare observed so far during the solar cycle 24: the X9.3 flare of September 6 and the off-limb X8.3 flare of September 10.
At the time of these two events, the Large-Yield Radiometer (LYRA) onboard PROBA2 was performing a special flare observation campaign, involving one of its spare units that is normally only used for calibration purposes. As this unit was only sporadically opened over the mission lifetime, it is relatively preserved from the ageing processes that otherwise affect the instrument, and it delivered very clear observations of both flares. In particular, the X9.3 flare produced a signature in the four channels of the instrument, of which two observe the EUV range, one the hydrogen Lyman-alpha line, and the last one the continuum around 2000 Angstroms. As flare observations are relatively rare in Lyman-alpha and almost non-existing in the continuum around 2000 Angstroms, this constitutes a rather unique set of observations. In contrast, the X8.3 flare only produced signatures in the two EUV channels. This presentation will describe the LYRA observations, compare both flares, and discuss the origin of the emitted signal in the four channels.- Publication:
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2018 Triennial Earth-Sun Summit (TESS)
- Pub Date:
- May 2018
- Bibcode:
- 2018tess.conf31903D