Diagnosing the time-dependence of active region core heating from the emission measure: II. Nanoflare trains

Abstract

The time-dependence of heating in solar active regions can be studied by analyzing the slope of the emission measure distribution cool-ward of the peak. In a previous study we showed that low-frequency heating can account for 0% to 77% of active region core emission measures. We now turn our attention to heating by a finite succession of impulsive events for which the timescale between events on a single magnetic strand is shorter than the cooling timescale. We refer to this scenario as a "nanoflare train" and explore a parameter space of heating and coronal loop properties with a hydrodynamic model. Our conclusions are: (1) nanoflare trains are consistent with 86% to 100% of observed active region cores when uncertainties in the atomic data are properly accounted for; (2) steeper slopes are found for larger values of the ratio of the train duration ${\Delta }_H$ to the post-train cooling and draining timescale ${\Delta }_C$, where ${\Delta }_H$ depends on the number of heating events, the event duration and the time interval between successive events (${\tau }_C$); (3) ${\tau }_C$ may be diagnosed from the width of the hot component of the emission measure provided that the temperature bins are much smaller than 0.1 dex; (4) the slope of the emission measure alone is not sufficient to provide information about any timescale associated with heating - the length and density of the heated structure must be measured for ${\Delta }_H$ to be uniquely extracted from the ratio ${\Delta }_H/{\Delta }_C$.

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• Can the Differential Emission Measure constrain the timescale of energy deposition
• Trigger Mechanism of Solar Subflares in a Braided Coronal Magnetic Structure
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• Inference of Heating Properties from "Hot" Non-flaring Plasmas in Active Region Cores. II. Nanoflare Trains
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• Influence of Electron-Impact Multiple Ionization on Equilibrium and Dynamic Charge State Distributions: A Case Study Using Iron
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• Calibration of the MaGIXS experiment II: Flight Instrument Calibration
• Plasma Diagnostics From Active Region and Quiet Sun Spectra Observed by Hinode/EIS: Quantifying the Departures from a Maxwellian Distribution