Synthetic Extreme-ultraviolet Emissions Modulated by Leaky Fast Sausage Modes in Solar Active Region Loops

TL;DR

This study investigates how leaky fast sausage modes in solar active region loops modulate EUV emissions, using MHD simulations and non-equilibrium ionization to understand observational signatures and damping behaviors.

Contribution

It introduces a comprehensive modeling approach combining MHD simulations and NEI effects to analyze EUV emission modulations by leaky FSMs in solar loops.

Findings

Density and intensity variations can be in phase or anti-phase depending on loop temperature.

NEI significantly affects intensity variations but has limited impact on Doppler measurements.

Damping times from intensity variations can reflect wave damping times under certain temperature conditions.

Abstract

We study the extreme-ultraviolet (EUV) emissions modulated by leaky fast sausage modes (FSMs) in solar active region loops and examine their observational signatures via spectrometers like EIS. After computing fluid variables of leaky FSMs with MHD simulations, we forward-model the intensity and spectral properties of the Fe X 185~\AA~and Fe XII 195~\AA~lines by incorporating non-equilibrium ionization (NEI) in the computations of the relevant ionic fractions. The damping times derived from the intensity variations are then compared with the wave values, namely the damping times directly found from our MHD simulations. Our results show that in the equilibrium ionization cases, the density variations and the intensity variations can be either in phase or in anti-phase, depending on the loop temperature. NEI considerably impacts the intensity variations but has only marginal effects on the derived Doppler velocity or Doppler width. We find that the damping time derived from the intensity can largely reflect the wave damping time if the loop temperature is not drastically different from the nominal formation temperature of the corresponding emission line. These results are helpful for understanding the modulations to the EUV emissions by leaky FSMs and hence helpful for identifying FSMs in solar active region loops.