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Frequency rising sub-THz emission from solar flare ribbons  

Galina Motorina   Submitted: 2018-10-11 01:09

Observations of solar flares at sub-THz frequencies (mm and sub-mm 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 s.f.u. at 0.4 THz) and fast variability on sub-second time scales. Although, many models has been put forward to explain the puzzling observations, none of them have 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.

Authors: Kontar, E. P.; Motorina, G. G.; Jeffrey, N. L. S.; Tsap, Y. T.; Fleishman, G. D.; Stepanov, A. V.
Projects: None

Publication Status: Astronomy and Astrophysics, accepted
Last Modified: 2018-10-15 14:52
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On the origin of 140 GHz emission from the 4 July 2012 solar flare  

Galina Motorina   Submitted: 2016-04-08 01:40

The sub-THz event observed on the 4 July 2012 with the Bauman Moscow State Technical University Radio Telescope RT-7.5 at 93 and 140 GHz as well as Kislovodsk and Metsahovi radio telescopes, Radio Solar Telescope Network (RSTN), GOES, RHESSI, and SDO orbital stations is analyzed. The spectral flux between 93 and 140 GHz has been observed increasing with frequency. On the basis of the SDO/AIA data the differential emission measure has been calculated. It is shown that the thermal coronal plasma with the temperature above 0.5 MK cannot be responsible for the observed sub-THz flare emission. The non-thermal gyrosynchrotron mechanism can be responsible for the microwave emission near 10 GHz but the observed millimeter spectral characteristics are likely to be produced by the thermal bremsstrahlung emission from plasma with a temperature of about 0.1 MK.

Authors: Yuriy T. Tsap, Victoria V. Smirnova, Alexander S. Morgachev, Galina G. Motorina, Eduard P. Kontar, Valery G. Nagnibeda, Polina V. Strekalova
Projects: None

Publication Status: Published at Advances in Space Research, V. 57, I. 7, p. 1449-1455; DOI: 10.1016/j.asr.2015.12.037
Last Modified: 2016-04-09 12:25
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Differential Emission Measure and Electron Distribution Function Reconstructed from RHESSI and SDO Observations  

Galina Motorina   Submitted: 2015-11-02 07:15

To solve a number of problems in solar physics related to mechanisms of energy release in solar corona parameters of hot coronal plasma are required, such as energy distribution, emission measure, differential emission measure, and their evolution with time. Of special interest is the distribution of solar plasma by energies, which can evolve from a nearly Maxwellian distribution to a distribution with a more complex structure during a solar flare. The exact form of this distribution for low-energy particles, which receive the bulk of flare energy, is still poorly known; therefore, detailed investigations are required. We present a developed method of simultaneous fitting of data from two spacecrafts Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) and Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), using a differential emission measure and a thin target model for the August 14, 2010 flare event.

Authors: G.G. Motorina and E. P. Kontar
Projects: None

Publication Status: Geomagnetism and Aeronomy. Vol. 55. No. 7. 2015.
Last Modified: 2015-11-02 10:52
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Abstracts by Author
Frequency rising sub-THz emission from solar flare ribbons
On the origin of 140 GHz emission from the 4 July 2012 solar flare
Differential Emission Measure and Electron Distribution Function Reconstructed from RHESSI and SDO Observations

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