Spectral Trends of Solar Bursts at Sub-THz Frequencies

Fernandes, L. O. T.; Kaufmann, P.; Correia, E.; Castro, C. G. Giménez de; Kudaka, A. S.; Marun, A.; Pereyra, P.; Raulin, J. P.; Válio, Adriana

doi:10.1007/s11207-016-1043-6

Cited by 6 publications

(3 citation statements)

References 26 publications

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“…Note, however, that at mm-waves the contribution from synchrotron emission from non-thermal electrons may become important or even dominant (e.g. Trottet et al 2002;Lüthi et al 2004b,a;Trottet et al 2011;Giménez de Castro et al 2013;Tsap et al 2016;Fernandes et al 2017).…”

Section: Discussionmentioning

confidence: 99%

Formation of the thermal infrared continuum in solar flares

Simões

Kerr

Fletcher

et al. 2017

A&A

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Aims. Observations of the Sun with the Atacama Large Millimeter Array have now started, and the thermal infrared will regularly be accessible from the NSF's Daniel K. Inouye Solar Telescope. Motivated by the prospect of these new data, and by recent flare observations in the mid infrared, we set out here to model and understand the source of the infrared continuum in flares, and to explore its diagnostic capability for the physical conditions in the flare atmosphere. Methods. We use the one-dimensional (1D) radiation hydrodynamics code RADYN to calculate mid-infrared continuum emission from model atmospheres undergoing sudden deposition of energy by non-thermal electrons. Results. We identify and characterise the main continuum thermal emission processes relevant to flare intensity enhancement in the mid-to far-infrared (2-200 µm) spectral range as free-free emission on neutrals and ions. We find that the infrared intensity evolution tracks the energy input to within a second, albeit with a lingering intensity enhancement, and provides a very direct indication of the evolution of the atmospheric ionisation. The prediction of highly impulsive emission means that, on these timescales, the atmospheric hydrodynamics need not be considered in analysing the mid-IR signatures.

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Section: Discussionmentioning

confidence: 99%

Formation of the thermal infrared continuum in solar flares

Simões

Kerr

Fletcher

et al. 2017

A&A

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“…In this connection, observations in the sub-THz frequency range of 10 2 -10 3 GHz (0.3 -3.0 mm) can be very useful since they allow us to extract important information about thermal and high-energy electrons (Raulin et al, 1999;Lüthi, Magun, and Miller, 2004;Fleishman and Kontar, 2010;Trottet et al, 2011;Krucker et al, 2013) but the origin of sub-THz emission is still unclear (Fleishman and Kontar, 2010;Krucker et al, 2013;Zaitsev, Stepanov, and Melnikov, 2013). In particular, spectral flux that increases with frequency (positive spectral slope) between 200 and 400 GHz has recently been recorded during the impulsive and gradual phases of some solar flares (Trottet et al, 2002;Lüthi, Magun, and Miller, 2004;Kaufmann et al, 2004Kaufmann et al, , 2009Silva et al, 2007;Fernandes et al, 2017). This contradicts the hypothesis of the gyrosynchrotron origin of sub-THz emission from a quasi-homogeneous source generated by the relativistic tail of non-thermal accelerated electrons (Trottet et al, 2002;Raulin et al, 2004;Lüthi, Magun, and Miller, 2004; and, hence, it needs further investigation.…”

Section: Introductionmentioning

confidence: 99%

Millimeter and X-Ray Emission from the 5 July 2012 Solar Flare

et al. 2018

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The 5 July 2012 solar flare (11:39 -11:49 UT) with an increasing millimeter spectrum between 93 and 140 GHz is considered. We use space and ground-based observations in X-ray, extreme ultraviolet, microwave, and millimeter wave ranges obtained with the Reuven Ramaty High-Energy Solar Spectroscopic Imager, Solar Dynamics Observatory (SDO), Geostationary Operat ional E nvironmental Satellite, Radio Solar Telescope Network, and Bauman Moscow State Technical University millimeter radio telescope RT-7.5. The main parameters of thermal and accelerated electrons were determined through Xray spectral fitting assuming the homogeneous thermal source and thick-target model. From the data of the Atmospheric Imaging Assembly/SDO and differential emission measure calculations it is shown that the thermal coronal plasma gives a negligible contribution to the millimeter flare emission. Model calculations suggest that the observed increase of millimeter spectral flux with frequency is determined by gyrosynchrotron emission of high-energy ( $≳ 300$

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“…Hence, they cannot be verified observationally. In general, any successful model should explain: (i) a sub-THz component that increases with frequency (Fernandes et al 2017), (ii) a large ∼ 10 4 s.f.u. flux at 200-400 GHz, (iii) a close association with non-thermal particles (Kaufmann et al 2009a), and (iv) the subsecond variations of the radio flux (Kaufmann et al 2009a).…”

Section: Introductionmentioning

confidence: 99%

Frequency rising sub-THz emission from solar flare ribbons

Kontar

Motorina

Jeffrey

et al. 2018

A&A

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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 ∼ 10 4 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 10 4 − 10 6 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.

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Spectral Trends of Solar Bursts at Sub-THz Frequencies

Cited by 6 publications

References 26 publications

Formation of the thermal infrared continuum in solar flares

Formation of the thermal infrared continuum in solar flares

Millimeter and X-Ray Emission from the 5 July 2012 Solar Flare

Frequency rising sub-THz emission from solar flare ribbons

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