Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations

Abstract

We exploit the high spatial resolution and high cadence of the Interface Region Imaging Spectrograph (IRIS) to investigate the response of the transition region and chromosphere to energy deposition during a small flare. Simultaneous observations from RHESSI provide constraints on the energetic electrons precipitating into the flare footpoints while observations of XRT, AIA, and EIS allow us to measure the temperatures and emission measures from the resulting flare loops. We find clear evidence for heating over an extended period on the spatial scale of a single IRIS pixel. During the impulsive phase of this event the intensities in each pixel for the Si IV 1402.770, C II 1334.535, Mg II 2796.354 and O I 1355.598 emission lines are characterized by numerous, small-scale bursts typically lasting 60s or less. Red shifts are observed in Si IV, C II, and Mg II during the impulsive phase. Mg II shows red-shifts during the bursts and stationary emission at other times. The Si IV and C II profiles, in contrast, are observed to be red-shifted at all times during the impulsive phase. These persistent red-shifts are a challenge for one-dimensional hydrodynamic models, which predict only short-duration downflows in response to impulsive heating. We conjecture that energy is being released on many small-scale filaments with a power-law distribution of heating rates.

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Cited by in corpus (12)

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• Spectroscopic Observations of Magnetic Reconnection and Chromospheric Evaporation in an X-shaped Solar Flare
• Electron Beams Cannot Directly Produce Coronal Rain
• IRIS Si IV Line Profiles at Flare Ribbons as Indications of Chromospheric Condensation
• Connecting Chromospheric Condensation Signatures to Reconnection Driven Heating Rates in an Observed Flare
• Exploring mutual information between IRIS spectral lines. II. Calculating the most probable response in all spectral windows
• Diagnosing the Optically Thick/Thin Features Using the Intensity Ratio of Si IV Resonance Lines in Solar Flares
• Simultaneous Observations of Chromospheric Evaporation and Condensation during a C-class Flare
• Revisiting the Spectral Features of Ellerman Bombs and UV Bursts. I. Radiative Hydrodynamic Simulations