Solar Physics

, Volume 286, Issue 1, pp 221–239

Sun-as-a-Star Observation of Flares in Lyman α by the PROBA2/LYRA Radiometer



There are very few reports of flare signatures in the solar irradiance at H i Lyman α at 121.5 nm, i.e. the strongest line of the solar spectrum. The LYRA radiometer onboard PROBA2 has observed several flares for which unambiguous signatures have been found in its Lyman-α channel. Here we present a brief overview of these observations followed by a detailed study of one of them: the M2 flare that occurred on 8 February 2010. For this flare, the flux in the LYRA Lyman-α channel increased by 0.6 %, which represents about twice the energy radiated in the GOES soft X-ray channel and is comparable with the energy radiated in the He ii line at 30.4 nm. The Lyman-α emission represents only a minor part of the total radiated energy of this flare, for which a white-light continuum was detected. Additionally, we found that the Lyman-α flare profile follows the gradual phase but peaks before other wavelengths. This M2 flare was very localized and had a very brief impulsive phase, but more statistics are needed to determine if these factors influence the presence of a Lyman-α flare signal strong enough to appear in the solar irradiance.


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Copyright information

© Springer Science+Business Media Dordrecht 2012

Authors and Affiliations

  • M. Kretzschmar
    • 1
    • 2
  • M. Dominique
    • 1
  • I. E. Dammasch
    • 1
  1. 1.Royal Observatory of Belgium/SIDCBrusselsBelgium
  2. 2.LPC2EUMR7328 CNRS/Université d’OrléansOrleansFrance

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