Static and Impulsive Models of Solar Active Regions

TL;DR

This paper compares static and impulsive models of solar active regions, showing that time-dependent nanoflare heating models better reproduce observed EUV and SXR loops and their spatial intensity variations.

Contribution

It demonstrates that impulsive nanoflare heating models can simultaneously match EUV and SXR observations, unlike static equilibrium models.

Findings

Static models fail to reproduce warm EUV loops.

Impulsive nanoflare models match both EUV and SXR loops.

AR morphology constrains impulsive heating properties.

Abstract

The physical modeling of active regions (ARs) and of the global coronal is receiving increasing interest lately. Recent attempts to model ARs using static equilibrium models were quite successful in reproducing AR images of hot soft X-ray (SXR) loops. They however failed to predict the bright EUV warm loops permeating ARs: the synthetic images were dominated by intense footpoint emission. We demonstrate that this failure is due to the very weak dependence of loop temperature on loop length which cannot simultaneously account for both hot and warm loops in the same AR. We then consider time-dependent AR models based on nanoflare heating. We demonstrate that such models can simultaneously reproduce EUV and SXR loops in ARs. Moreover, they predict radial intensity variations consistent with the localized core and extended emissions in SXR and EUV AR observations respectively. We finally show how the AR morphology can be used as a gauge of the properties (duration, energy, spatial dependence, repetition time) of the impulsive heating.