Search

The temporal evolution of thermal bremsstrahlung in the sub-terahertz range is calculated for F-CHROMA models of the flare chromosphere and transition region (https://www.fchroma.org). These models are calculated based on the numerical solution of the system of equations of radiation hydrodynamics with the RADYN code, which describes the response of chromospheric plasma to the flux of accelerated electrons in the form of a triangular pulse. It is found that the positive slope of the spectrum in the frequency range of 93–400 GHz is formed during the entire burst. The sub-THz radiation peak can be both ahead and behind the maximum of the function of the injection of energetic electrons depending on the number and index of the spectrum of precipitating particles. In some cases, the time profile of the sub-THz radiation is quite complex and pulsating due to gas-dynamic phenomena in the chromosphere and transition region. [ABSTRACT FROM AUTHOR]

Abstract: Millimeter (93 and 140 GHz) emission of the М6.4 solar flare detected on April 2, 2017 in the NOAA 12644 active region by the RT-7.5 telescope of the Bauman Moscow State Technical University is analyzed using the observational data provided by the Radio Solar Telescope Network (4.9, 8.8, and 15.4 GHz); the SDO/AIA satellites (Etreme Ultraviolet); and GOES, RHESSI, and Konus-Wind (X-rays). It is found that the spectral flux density of millimeter emission increases with frequency throughout the entire burst. The similarity between the profiles of millimeter and soft-X-ray radiation suggests that the burst is of a thermal nature. It follows from the results of calculations of the differential emission measure of coronal plasma based on the SDO/AIA data that its contribution to millimeter emission of the flare is negligible. The simulation of thermal emission of chromospheric flare plasma in the model of Machado (Machado et al., 1980) yields millimeter fluxes that are by several times lower than the observed ones. The physical implications of these results are discussed. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.1134/S0016793221070288 [ABSTRACT FROM AUTHOR]