Observation of a Flare and Filament Eruption in Lyman-$\alpha $ on 8 September 2011 by the PRoject for OnBoard Autonomy/Large Yield Radiometer (PROBA2/LYRA)

Abstract : The Large Yield Radiometer (LYRA) instrument onboard the PRoject for OnBoard Autonomy (PROBA2) observes the solar irradiance in four channels in the UV–EUV. One of these channels is centered around the hydrogen line at 121.6 nm. The solar Lyman-α emission line is an optically thick line mostly formed in the chromosphere. Although it is one of the strongest lines of the solar spectrum, only a limited number of instruments provided observations of solar flares in Lyman-α, and those observations differ significantly in shape, durations, and amplitude. We focus on an event that happened on 8 September 2011 (SOL2011-09-08T15:46). This event, an M6.7 flare, was associated with a filament eruption that happened during the decaying phase of the flare. Most of the irradiance fluctuations observed in the Lyman-α time series are synchronized with nonthermal emission fluctuations, as is predicted by flare models. However, there is a late-phase peak in Lyman-α observations that rather correlates with the timing of the filament eruption. We demonstrate that the eruption of the filament is at the origin of this peak.