Solar Physics

, Volume 290, Issue 10, pp 2809–2826 | Cite as

Origin of the 30 THz Emission Detected During the Solar Flare on 2012 March 13 at 17:20 UT

  • G. Trottet
  • J.-P. RaulinEmail author
  • A. Mackinnon
  • G. Giménez de Castro
  • P. J. A. Simões
  • D. Cabezas
  • V. de La Luz
  • M. Luoni
  • P. Kaufmann


Solar observations in the infrared domain can bring important clues on the response of the low solar atmosphere to primary energy released during flares. At present, the infrared continuum has been detected at 30 THz (10 μm) in only a few flares. SOL2012-03-13, which is one of these flares, has been presented and discussed in Kaufmann et al. (Astrophys. J. 768, 134, 2013). No firm conclusions were drawn on the origin of the mid-infrared radiation. In this work we present a detailed multi-frequency analysis of the SOL2012-03-13 event, including observations at radio-millimeter and submillimeter wavelengths, in hard X-rays (HXR), gamma-rays (GR), \(\mathrm{H}\alpha\), and white light. The HXR/GR spectral analysis shows that SOL2012-03-13 is a GR line flare and allows estimating the numbers of and energy contents in electrons, protons, and \(\alpha\) particles produced during the flare. The energy spectrum of the electrons producing the HXR/GR continuum is consistent with a broken power-law with an energy break at \({\sim}\,800~\mbox{keV}\). We show that the high-energy part (above \({\sim}\, 800~\mbox{keV}\)) of this distribution is responsible for the high-frequency radio emission (\({>}\, 20~\mbox{GHz}\)) detected during the flare. By comparing the 30 THz emission expected from semi-empirical and time-independent models of the quiet and flare atmospheres, we find that most (\({\sim}\,80~\%\)) of the observed 30 THz radiation can be attributed to thermal free–free emission of an optically thin source. Using the F2 flare atmospheric model (Machado et al. in Astrophys. J. 242, 336, 1980), this thin source is found to be at temperatures T \({\sim}\,8000~\mbox{K}\) and is located well above the minimum temperature region. We argue that the chromospheric heating, which results in 80 % of the 30 THz excess radiation, can be due to energy deposition by nonthermal flare-accelerated electrons, protons, and \(\alpha\) particles. The remaining 20 % of the 30 THz excess emission is found to be radiated from an optically thick atmospheric layer at T \({\sim}\, 5000~\mbox{K}\), below the temperature minimum region, where direct heating by nonthermal particles is insufficient to account for the observed infrared radiation.


Radio bursts, microwave X-ray bursts, association with flares X-ray burst, spectrum Chromosphere, models Heating, chromospheric Heating, in flares 



The authors thank G. Chambe and K.-L. Klein for their suggestions and critical comments. We thank STFC for support through grant ST/L000741/1 (ALM). Some of the ALM contribution was made while on study leave at CRAAM, Mackenzie Presbyterian University, São Paulo with FAPESP financial support. PJAS acknowledges the European Community’s Seventh Framework Programme (FP7/2007 – 2013) under grant agreement no. 606862 (F-CHROMA) for financial support. VDL acknowledges Catedras-CONACyT project 1045. This research was partially supported by the Brazilian agencies FAPESP (contract 2013/24155-3, 2015/13596-4), CNPq (contract 312788/2013-4), Mackpesquisa and U.S. AFOSR. We are grateful to the referee, Säm Krucker, for his constructive recommendations.


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Copyright information

© Springer Science+Business Media Dordrecht 2015

Authors and Affiliations

  • G. Trottet
    • 1
  • J.-P. Raulin
    • 2
    Email author
  • A. Mackinnon
    • 3
  • G. Giménez de Castro
    • 2
  • P. J. A. Simões
    • 3
  • D. Cabezas
    • 2
  • V. de La Luz
    • 4
  • M. Luoni
    • 5
  • P. Kaufmann
    • 2
    • 6
  1. 1.LESIA, Observatoire de ParisPSL Research University, CNRS, Sorbonne UniversitésMeudonFrance
  2. 2.CRAAM Universidade Presbiteriana MackenzieSão PauloBrazil
  3. 3.School of Physics and Astronomy, SUPAUniversity of GlasgowGlasgowUK
  4. 4.SCiESMEX, Instituto de Geofisica, Unidad MichoacanUniversidad Nacional Autonoma de MexicoMoreliaMexico
  5. 5.IAFEUniversity of Buenos AiresBuenos AiresArgentina
  6. 6.CCSUniversity of CampinasCampinasBrazil

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