Frequency rising sub-THz emission from solar flare ribbons

Abstract

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.

arXiv comment6 pages, 3 figures, 2 tables, A&A, accepted

References in corpus (26)

• Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares
• Deducing Electron Properties From Hard X-Ray Observations
• Global Energetics of Solar Flares: V. Energy Closure in Flares and Coronal Mass Ejections
• Turbulent kinetic energy in the energy balance of a solar flare
• Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop
• Collisional relaxation of electrons in a warm plasma and accelerated nonthermal electron spectra in solar flares
• Sub-THz radiation mechanisms in solar flares
• The Ribbon-Like Hard X-Ray Emission in a Sigmoidal Solar Active Region
• The sub-arcsecond hard X-ray structure of loop footpoints in a solar flare
• Broadband microwave burst produced by electron beams
• Predictions of energy and helicity in four major eruptive solar flares
• Observing the formation of flare-driven coronal rain
• On the Brightening Propagation of Post-Flare Loops Observed by TRACE
• RHESSI and SDO/AIA observations of the chromospheric and coronal plasma parameters during a solar flare
• Height structure of X-ray, EUV and white-light emission in a solar flare
• A Cold Flare With Delayed Heating
• Sub-terahertz, microwaves and high energy emissions during the December 6, 2006 flare, at 18:40 UT
• Anomalous Cooling of Coronal Loops with Turbulent Suppression of Thermal Conduction
• Statistically-derived flaring chromospheric-coronal density structure from non-thermal X-ray observations of the Sun
• Transition Region Emission and Energy Input to Thermal Plasma During the Impulsive Phase of Solar Flares
• Origin of the submillimeter radio emission during the time-extended phase of a solar flare
• Rapid pulsations in sub-THz solar bursts
• On the origin of 140 GHz emission from the 4 July 2012 solar flare
• Transition Region Emission from Solar Flares during the Impulsive Phase
• The contribution of microbunching instability to solar flare emission in the GHz to THz range of frequencies
• The collisional relaxation of electrons in hot flaring plasma and inferring the properties of solar flare accelerated electrons from X-ray observations

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• Pre-impulsive and Impulsive Phases of the Sub-Terahertz Flare of March 28, 2022