Origin of the 30 THz emission detected during the 2012 March 13 solar flare at 17:20 UT

Abstract

Solar observations in the infrared domain can bring important clues on the response of the low solar atmosphere to primary energy released during flares. At present the infrared continuum has been detected at 30 THz (10 $\mu$m) in only a few flares. In this work we present a detailed multi-frequency analysis of SOL2012-03-13, including observations at radio millimeter and sub-millimeter wavelengths, in hard X-rays (HXR), gamma-rays (GR), H-alpha, and white-light. HXR/GR spectral analysis shows that the event is a GR line flare and allows estimating the numbers of and energy contents in electrons, protons and alpha particles produced during the flare. The energy spectrum of the electrons producing the HXR/GR continuum is consistent with a broken power-law with an energy break at ~800 keV. It is shown that the high-energy part (above ~800 keV) of this distribution is responsible for the high-frequency radio emission (> 20 GHz) detected during the flare. By comparing the 30 THz emission expected from semi-empirical and time-independent models of the quiet and flare atmospheres, we find that most (~80%) of the observed 30 THz radiation can be attributed to thermal free-free emission of an optically-thin source. Using the F2 flare atmospheric model this thin source is found to be at temperatures T~8000 K and is located well above the minimum temperature region. We argue that the chromospheric heating, which results in 80% of the 30 THz excess radiation, can be due to energy deposition by non-thermal flare accelerated electrons, protons and alpha particles. The remaining 20% of the 30 THz excess emission is found to be radiated from an optically-thick atmospheric layer at T~5000 K, below the temperature minimum region, where direct heating by non-thermal particles is insufficient to account for the observed infrared radiation.

22 pages, 7 figures, accepted for publication in Solar Physics

References in corpus (9)

• Big-Bang Nucleosynthesis
• The Fermi Gamma-Ray Burst Monitor
• Physical Properties of White-Light Sources in the 2011 Feb 15 Solar Flare
• Response of optical hydrogen lines to beam heating: I. Electron beams
• A bright impulsive solar burst detected at 30 THz
• Bright 30 THz Impulsive Solar Bursts
• Synthetic Spectra of Radio, Millimeter, Sub-millimeter and Infrared Regimes with NLTE approximation
• Pakal: A Three-dimensional Model to Solve the Radiative Transfer Equation
• Association of mid-infrared solar plages with Calcium K line emissions and magnetic structures

Cited by in corpus (15)

• Solar science with the Atacama Large Millimeter/submillimeter Array - A new view of our Sun
• Characteristics of Sustained >100 MeV Gamma-ray Emission Associated with Solar Flares
• Estimation of a Coronal Mass Ejection Magnetic Field Strength using Radio Observations of Gyrosynchrotron Radiation
• Formation of the thermal infrared continuum in solar flares
• Parameterizations of Chromospheric Condensations in dG and dMe Model Flare Atmospheres
• Spectral and Imaging Observations of a White-light Flare in the Mid-Infrared
• Reproducing Type II White-Light Solar Flare Observations with Electron and Proton Beam Simulations
• Data-Constrained Solar Modeling with GX Simulator
• A solar flare driven by thermal conduction observed in mid-infrared
• FLUKA Simulations of Pion Decay Gamma-radiation from Energetic Flare Ions
• The Chromospheric Solar Limb Brightening at Radio, Millimeter, Sub-millimeter, and Infrared Wavelengths
• HATS: A Ground-Based Telescope to Explore the THz Domain
• Non-Linear Convergence of Solar-like Stars Chromospheres using Millimeter, Sub-millimeter, and Infrared Observations
• Submillimeter radiation as the thermal component of the Neupert Effect
• Thyr: A Volumetric Ray-Marching Tool for Simulating Microwave Emission