Frequency rising sub-THz emission from solar flare ribbons

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

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Abstract

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
Article numberA95
JournalAstronomy and Astrophysics
Volume620
Early online date4 Dec 2018
DOIs
Publication statusPublished - Dec 2018
Externally publishedYes

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