The Sun as a star: observations of white-light flares

By M. Kretzschmar. 2011

164 citations recorded by the source corpus.

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).

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/c4bbc88b9b6310db24a69d62dddab9e74eb6626a

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In Astronomy and Astrophysics

Citations in the corpus

The standard flare model in three dimensions II: upper limit on solar flare energy (2012, methodology): “Typical solar active region parameters resulted in typically observed magnetic fluxes (Parnell et al. 2009; Zhang et al. 2010) and flare energies (Kretzschmar 2011; Schrijver et al. 2012).”
SUPERFLARES ON SOLAR-TYPE STARS OBSERVED WITH KEPLER. I. STATISTICAL PROPERTIES OF SUPERFLARES (2013, background): “ESTIMATING TOTAL FLARE ENERGY FROM GOES X-RAY FLUX BASED ON KRETZSCHMAR’S RELATION Kretzschmar (2011) derived the empirical relation between the bolometric flux of flare and GOES X-ray flux as Fbol = 2.4 × 1012F 0.65GOES.”
The standard flare model in three dimensions - I. Strong-to-weak shear transition in post-flare loops (2012, result): “On the other hand, they are contradictory with the findings of Kretzschmar (2011) who estimated lower flare energies, and with those of Emslie et al. (2005) who estimated that both the flare and the CME should have comparable energies.”
Estimating the frequency of extremely energetic solar events, based on solar, stellar, lunar, and terrestrial records (2012, methodology): “In order to convert these energies to estimated bolometric fluences we use the finding that approximately 15% of the event energy is emitted in the coronal EUV, as derived for larger flares [Kretzschmar , 2011], although this has not been verified for the smaller events observed in the EUV only.”
Water loss from terrestrial planets orbiting ultracool dwarfs: implications for the planets of TRAPPIST-1 (2016, background): “Let us consider here that the flare released in the XUV range 20% of the energy it released in the 400–900 nm band (this proportion has been measured for Sun flares in Kretzschmar 2011).”
25 Years of Self-Organized Criticality: Solar and Astrophysics (2014, background): “Bottom: The size distribution of GOES fluxes inferred from the scaling law of Kretzschmar (2011) yields a powerlaw slope of αP = 1.88± 0.09 (Aschwanden 2014). ejects shocked matter, or even by galactic collisions, which cause compression of matter and tidal forces.”