Frequency rising sub-THz emission from solar flare ribbons

Kontar, E. P., Motorina, G. G., Jeffrey, Natasha, Tsap, Y. T., Fleishman, G. D. and Stepanov, A. V. (2018) Frequency rising sub-THz emission from solar flare ribbons. Astronomy & Astrophysics, 620. A95. ISSN 0004-6361

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Official URL: https://doi.org/10.1051/0004-6361/201834124

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 104 − 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.

Item Type: Article
Uncontrolled Keywords: Sun: flares; Sun: chromosphere; Sun: X-rays; gamma rays; Sun: magnetic fields; Sun: activity; Sun: radio radiation
Subjects: F300 Physics
F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Elena Carlaw
Date Deposited: 03 Sep 2019 12:58
Last Modified: 11 Oct 2019 12:49
URI: http://nrl.northumbria.ac.uk/id/eprint/40493

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