Solar Physics

, Volume 286, Issue 1, pp 221–239 | Cite as

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.


Flare Light Curf Impulsive Phase Orbital Variation Gradual Phase 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



LYRA is a project of the Centre Spatial de Liège, the Physikalisch-Meteorologisches Observatorium Davos, the Royal Observatory of Belgium funded by the Belgian Federal Science Policy Office (BELSPO), and the Swiss Bundesamt für Bildung und Wissenschaft. SWAP is a project of the Centre Spatial de Liège and the Royal Observatory of Belgium funded by the Belgian Federal Science Policy Office (BELSPO). Both instruments are onboard the ESA PROBA2 mission. Hinode is a Japanese mission developed and launched by ISAS/JAXA in partnership with NAOJ and in collaboration with NASA (USA) and STFC (UK). It is operated by these agencies in co-operation with ESA and NSC (Norway). The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a NASA small explorer mission. CELIAS/SEM and VIRGO are experiments on the Solar Heliospheric Observatory (SOHO) spacecraft. SOHO is a mission of international collaboration between ESA and NASA. Suzaku is a collaborative mission between the space agencies of Japan (JAXA) and the USA (NASA). The white-light images are from the Global Oscillation Network Group (GONG) Program, managed by the National Solar Observatory, which is operated by AURA, Inc. The data were acquired by the instruments operated by the Cerro Tololo Interamerican Observatory. The H-α images are from the Kanzelhöhe Solar Observatory, operated by the Institute for Geophysics, Astrophysics, and Meteorology (IGAM) of the University of Graz (Austria). This work has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under the grant agreement n° 261948 (ATMOP project, ).


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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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