Solar Physics

, 294:150 | Cite as

Submillimeter Radiation as the Thermal Component of the Neupert Effect

  • Jorge F. Valle Silva
  • C. Guillermo Giménez de CastroEmail author
  • Paulo J. A. Simões
  • Jean-Pierre Raulin


The Neupert effect is the empirical observation that the temporal evolution of non-thermal emission (e.g. hard X-rays) is frequently proportional to the temporal derivative of the thermal emission flux (soft X-rays), or vice versa, that time-integrated non-thermal flux is proportional to thermal flux. We analyzed the GOES M2.2 event SOL2011-02-14T17:25, and we found that the 212 GHz emission plays quite well the role of the thermal component of the Neupert effect. We show that the maximum of the hard X-ray flux for energies above 50 keV is coincident in time with the temporal derivative of the 212 GHz flux, within the uncertainties. The microwave flux density at 15.4 GHz, produced by optically thin gyrosynchrotron mechanism, and hard-X rays above 25 keV mark the typical impulsive phase, and they have similar temporal evolution. On the other hand, the 212 GHz emission is delayed by about 25 seconds with respect to the microwave and hard X-ray peak. We argue that this delay cannot be explained by magnetic trapping of non-thermal electrons. With all of the observational evidence, we suggest that the 212 GHz emission is produced by thermal bremsstrahlung, initially in the chromosphere, and shifting to optically thin emission from the hot coronal loops at the end of the gradual phase.


Flares, dynamics Flares, X-rays Flares submillimeter radiation Chromospheric evaporation 



The authors are grateful to Hugh Hudson for his enlightening comments about the Neupert effect and its history. J.F. Valle Silva acknowledges FAPESP for the support during his PhD Thesis (grant 2012/1619-9) and CAPES for the Postdoctoral PNPD contract. G. Giménez de Castro and J.-P. Raulin acknowledge CNPq (contracts 305203/2016-9 and 312066/2016-3). The research leading to these results has received funding from the European Community’s Seventh Framework Program (FP7/2007-2013) under grant agreement no. 606862 (F-CHROMA), CAPES grant 88881.310386/2018-01, FAPESP grant 2013/24155-3 and the US Air Force Office for Scientific Research (AFOSR) grant FA9550-16-1-0072. AIA data are courtesy of NASA/SDO and the AIA science team. This work is based on data acquired at Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juán.

Disclosure of Potential Conflicts of Interest

The authors declare that they have no conflicts of interest.


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Copyright information

© Springer Nature B.V. 2019

Authors and Affiliations

  1. 1.Centro de Rádio Astronomia e Astrofísica Mackenzie, Escola de EngenhariaUniversidade Presbiteriana MackenzieSão PauloBrazil
  2. 2.Instituto e Astronomía y Física del EspacioCONICET-UBABuenos AiresArgentina
  3. 3.SUPA School of Physics & AstronomyUniversity of GlasgowGlasgowUK

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