First Detection of Solar Flare Emission in Mid-ultraviolet Balmer Continuum

Marie Dominique (1, 2) , Andrei Zhukov (1) , Petr Heinzel (3) , Ingolf E. Dammasch (1) , Laurence Wauters (1) , Laurent Dolla (1) , Sergei Shestov (1) , Matthieu Kretzschmar (4) , Janet Machol , Giovanni Lapenta

1 STCE - Solar-Terrestrial Centre of Excellence [Brussels]
2 KU Leuven - Catholic University of Leuven - Katholieke Universiteit Leuven
3 ASU / CAS - Astronomical Institute of the Czech Academy of Sciences
4 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace

We present the first detection of solar flare emission at middle-ultraviolet wavelengths around 2000Å by the channel 2 of the Large-Yield RAdiometer (LYRA) onboard the PROBA2 mission. The flare (SOL20170906) was also observed in the channel 1 of LYRA centered at the H I Lyman-α line at 1216Å, showing a clear non-thermal profile in both channels. The flare radiation in channel 2 is consistent with the hydrogen Balmer continuum emission produced by an optically thin chromospheric slab heated up to 10000 K. Simultaneous observations in channels 1 and 2 allow the separation of the line emission (primarily from the Lyman-α line) from the Balmer continuum emission. Together with the recent detection of the Balmer continuum emission in the near-ultraviolet by IRIS, the LYRA observations strengthen the interpretation of broadband flare emission as the hydrogen recombination continua originating in the chromosphere.

Domains: Sciences of the Universe [physics]

Marie Dominique, Andrei Zhukov, Petr Heinzel, Ingolf E. Dammasch, Laurence Wauters, et al.. First Detection of Solar Flare Emission in Mid-ultraviolet Balmer Continuum. The Astrophysical journal letters, 2018, 867 (2), pp.L24. ⟨10.3847/2041-8213/aaeace⟩. ⟨insu-02940873⟩