Volume 530, June 2011
|Number of page(s)||7|
|Published online||16 May 2011|
The Sun as a star: observations of white-light flares
LPC2E, UMR 6115 CNRS and University of Orléans, 3a Av. de la recherche scientifique, 45071 Orléans, France
Received: 14 October 2010
Accepted: 1 April 2011
Context. Solar flares radiate energy at all wavelengths, but the spectral distribution of this energy is still poorly known. White-light continuum emission is sometimes observed, and these flares are then called “white-light flares” (WLFs).
Aims. We investigate if all flares are WLFs and how the radiated energy is distributed spectrally.
Methods. We perform a superposed epoch analysis of spectral and total irradiance measurements obtained since 1996 by the SOHO and GOES spacecraft at various wavelengths, from soft X-rays to the visible domain.
Results. The long-term record of solar irradiance and the excellent duty cycle of the measurements allow us to detect a signal in visible irradiance even for moderate (C-class) flares mainly during the impulsive phase. We identify this signal as continuum emission emitted by WLFs and find that it is consistent with a blackbody emission at ~9000 K. We estimate the contribution of the WL continuum for several sets of flares and find it to be about 70% of the total radiated energy. We re-analyse the X17 flare that occurred on 28 October 2003 and find similar results.
Conclusions. We show that most of the flares – if not all – are WLFs and that the white-light continuum is the main contributor to the total radiated energy; this continuum is consistent with a blackbody spectrum at ~9000 K. These observational results are important for understanding the physical mechanisms during flares and possibly suggest a contribution of flares to the variations of the total solar irradiance (TSI).
Key words: sun: flares / stars: flare / Sun: activity / solar-terrestrial relations
© ESO, 2011
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.