Formation of the thermal infrared continuum in solar flares

Abstract

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. We use the 1D radiation hydrodynamics code RADYN to calculate mid-infrared continuum emission from model atmospheres undergoing sudden deposition of energy by non-thermal electrons. We identify and characterise the main continuum thermal emission processes relevant to flare intensity enhancement in the mid- to far-infrared (2-200 $\mu$m) 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 ionization. The prediction of highly impulsive emission means that, on these timescales, the atmospheric hydrodynamics need not be considered in analysing the mid-IR signatures.

accepted for publication in A&A

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• The F-CHROMA grid of 1D RADYN flare models
• The Atmospheric Response to High Nonthermal Electron Beam Fluxes in Solar Flares. II. Hydrogen Broadening Predictions for Solar Flare Observations with the Daniel K. Inouye Solar Telescope
• RADYNVERSION: Learning to Invert a Solar Flare Atmosphere with Invertible Neural Networks
• First Spectral Analysis of a Solar Plasma Eruption Using ALMA
• Prospects of Detecting Non-thermal Protons in Solar Flares via Lyman Line Spectroscopy: Revisiting the Orrall-Zirker Effect
• Radiative losses in the chromosphere during a C-class flare
• Submillimeter radiation as the thermal component of the Neupert Effect
• Thyr: A Volumetric Ray-Marching Tool for Simulating Microwave Emission
• Solar Flare Heating with Turbulent Suppression of Thermal Conduction
• Specialist Discussion Meeting: 3D structure of the flare chromosphere