Ultra-narrow Negative Flare Front Observed in Helium-10830~Å using the 1.6 m New Solar Telescope

Abstract

Solar flares are sudden flashes of brightness on the Sun and are often associated with coronal mass ejections and solar energetic particles which have adverse effects in the near Earth environment. By definition, flares are usually referred to bright features resulting from excess emission. Using the newly commissioned 1.6~m New Solar Telescope at Big Bear Solar Observatory, here we show a striking "negative" flare with a narrow, but unambiguous "dark" moving front observed in He I 10830 Å, which is as narrow as 340 km and is associated with distinct spectral characteristics in H-alpha and Mg II lines. Theoretically, such negative contrast in He I 10830 Å can be produced under special circumstances, by nonthermal-electron collisions, or photoionization followed by recombination. Our discovery, made possible due to unprecedented spatial resolution, confirms the presence of the required plasma conditions and provides unique information in understanding the energy release and radiative transfer in astronomical objects.

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• Blue wing enhancement of the chromospheric Mg II h and k lines in a solar flare
• 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
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• Solar Flare Ribbon Fronts I: Constraining flare energy deposition with IRIS spectroscopy
• RADYN simulations of non-thermal and thermal models of Ellerman bombs
• Observations and simulations of the Na I D1 line profiles in an M-class solar flare
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• Exploring mutual information between IRIS spectral lines. II. Calculating the most probable response in all spectral windows
• Multi-Passband Observations of A Solar Flare over the He I 10830 Å line
• Chromospheric velocities in an M3.2 flare using He I 1083.0 nm and Ca II 854.2 nm
• Negative flare in the He I 10830 Å line in facula
• Comparison of Enhanced Absorption in He I 10830 Å in Observations and Modeling During the Early Phase of a Solar Flare
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• A new view of the solar interface region from the Interface Region Imaging Spectrograph (IRIS)
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