Spectroscopic Observations of Hot Lines Constraining Coronal Heating in Solar Active Regions

Abstract

EUV observations of warm coronal loops suggest that they are bundles of unresolved strands that are heated impulsively to high temperatures by nanoflares. The plasma would then have the observed properties (e.g., excess density compared to static equilibrium) when it cools into the 1-2 MK range. If this interpretation is correct, then very hot emission should be present outside of proper flares. It is predicted to be vey faint, however. A critical element for proving or refuting this hypothesis is the existence of hot, very faint plasmas which should be at amounts predicted by impulsive heating. We report on the first comprehensive spectroscopic study of hot plasmas in active regions. Data from the EIS spectrometer on Hinode were used to construct emission measure distributions in quiescent active regions in the 1-5 MK temperature range. The distributions are flat or slowly increasing up to approximately 3 MK and then fall off rapidly at higher temperatures. We show that active region models based on impulsive heating can reproduce the observed EM distributions relatively well. Our results provide strong new evidence that coronal heating is impulsive in nature.

ApJ, 2009, in press

References in corpus (7)

• Highly Efficient Modeling of Dynamic Coronal Loops
• EUV emission lines and diagnostics observed with Hinode/EIS
• Observations of Active Region Loops with the EUV Imaging Spectrometer on Hinode
• Hinode X-Ray Telescope Detection of Hot Emission from Quiescent Active Regions: A Nanoflare Signature?
• Non-equilibrium of Ionization and the Detection of Hot Plasma in Nanoflare-heated Coronal Loops
• Static and Impulsive Models of Solar Active Regions
• Diagnostic of the temperature and differential emission measure (DEM) based on Hinode/XRT data

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• The Heating of Solar Coronal Loops by Alfven Wave Turbulence
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• Comparison of Hinode/XRT and RHESSI detection of hot plasma in the non-flaring solar corona
• Constraining Hot Plasma in a Non-flaring Solar Active Region with FOXSI Hard X-ray Observations
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• Thermal structure of hot non-flaring corona from Hinode/EIS
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• Heating Mechanisms for Intermittent Loops in Active Region Cores from AIA/SDO EUV Observations
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