Non-equilibrium Ionization Effects on Extreme-Ultraviolet Emissions Modulated by Standing Sausage Modes in Coronal Loops

Abstract

Forward-modeling the emission properties in various passbands is important for confidently identifying magnetohydrodynamic waves in the structured solar corona. We examine how Non-equilibrium Ionization (NEI) affects the Extreme Ultraviolet (EUV) emissions modulated by standing fast sausage modes (FSMs) in coronal loops, taking the Fe IX 171 Å and Fe XII 193 Å emission lines as examples. Starting with the expressions for linear FSMs in straight cylinders, we synthesize the specific intensities and spectral profiles for the two spectral lines by incorporating the self-consistently derived ionic fractions in the relevant contribution functions. We find that relative to the case where Equilibrium Ionization (EI) is assumed, NEI considerably impacts the intensity modulations, but shows essentially no effect on the Doppler velocities or widths. Furthermore, NEI may affect the phase difference between intensity variations and those in Doppler widths for Fe XII 193 Å when the line-of-sight is oblique to the loop axis. While this difference is $180^{\circ }$ when EI is assumed, it is $\sim 90^{\circ }$ when NEI is incorporated for the parameters we choose. We conclude that in addition to viewing angles and instrumental resolutions, NEI further complicates the detection of FSMs in spectroscopic measurements of coronal loops in the EUV passband.

4 figures, accepted for publication in the ApJ

References in corpus (8)

• Global sausage oscillation of solar flare loops detected by the Interface Region Imaging Spectrograph
• Observation of multiple sausage oscillations in cool postflare loop
• Inferring flare loop parameters with measurements of standing sausage modes
• Forward Modelling of Standing Kink Modes in Coronal Loops I. Synthetic Views
• Fast sausage modes in magnetic tubes with continuous transverse profiles: effects of a finite plasma beta
• Standing sausage modes in coronal loops with plasma flow
• Kinetic Simulation of Slow Magnetosonic Waves and Quasi-periodic Upflows in the Solar Corona
• Sensitivity of Coronal Loop Sausage Mode Frequencies and Decay Rates to Radial and Longitudinal Density Inhomogeneities: A Spectral Approach

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• Accelerating and Supersonic Density Fluctuations in Coronal Hole Plumes: Signature of Nascent Solar Winds
• Synthetic Extreme-ultraviolet Emissions Modulated by Leaky Fast Sausage Modes in Solar Active Region Loops
• Composition Comparison between ICMEs from Active Regions and Quiet-Sun Regions