Frequency rising sub-THz emission from solar flare ribbons

E. P. Kontar, G. G. Motorina, N. L.S. Jeffrey, Y. T. Tsap, Gregory Fleishman, A. V. Stepanov

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Observations of solar flares at sub-THz frequencies (millimetre and sub-millimetre wavelengths) over the last two decades often show a spectral component rising with frequency. Unlike a typical gyrosynchrotron spectrum decreasing with frequency or a weak thermal component from hot coronal plasma, the observations can demonstrate a high flux level (up to ∼104 solar flux units at 0.4 THz) and fast variability on sub-second timescales. Although, many models have been put forward to explain the puzzling observations, none of them has clear observational support. Here we propose a scenario to explain the intriguing sub-THz observations. We show that the model, based on free-free emission from the plasma of flare ribbons at temperatures 104â-Â 106 K, is consistent with all existing observations of frequency-rising sub-THz flare emission. The model provides a temperature diagnostic of the flaring chromosphere and suggests fast heating and cooling of the dense transition region plasma.

Original languageEnglish (US)
Article numberA95
JournalAstronomy and Astrophysics
StatePublished - Dec 1 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Gamma rays
  • Sun: Activity
  • Sun: X-rays
  • Sun: chromosphere
  • Sun: flares
  • Sun: magnetic fields
  • Sun: radio radiation


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