Inferring flare loop parameters with measurements of standing sausage modes

Abstract

Standing fast sausage modes in flare loops were suggested to account for a considerable number of quasi-periodic pulsations (QPPs) in the light curves of solar flares. This study continues our investigation into the possibility to invert the measured periods $P$ and damping times $\tau$ of sausage modes to deduce the transverse Alfvén time $R/v_{\mathrm{Ai}}$, density contrast ${\rho }_{\mathrm{i}}/{\rho }_{\mathrm{e}}$, and the steepness of the density distribution transverse to flare loops. A generic dispersion relation (DR) governing linear sausage modes is derived for pressureless cylinders where density inhomogeneity of arbitrary form takes place within the cylinder. We show that in general the inversion problem is under-determined for QPP events where only a single sausage mode exists, be the measurements spatially resolved or unresolved. While $R/v_{\mathrm{Ai}}$ can be inferred to some extent, the range of possible steepness parameters may be too broad to be useful. However, for spatially resolved measurements where an additional mode is present, it is possible to deduce self-consistently ${\rho }_{\mathrm{i}}/{\rho }_{\mathrm{e}}$, the profile steepness, and the internal Alfvén speed $v_{\mathrm{Ai}}$. We show that at least for a recent QPP event that involves a fundamental kink mode in addition to a sausage one, flare loop parameters are well constrained, even if the specific form of the transverse density distribution remains unknown. We conclude that spatially resolved, multi-mode QPP measurements need to be pursued for inferring flare loop parameters.

25 pages, 12 figures, accepted for publication in Solar Physics

References in corpus (3)

• Alfven Waves in the Lower Solar Atmosphere
• Advances in Observing Various Coronal EUV Waves in the SDO Era and Their Seismological Applications (Invited Review)
• Analytic approximate seismology of transversely oscillating coronal loops

Cited by in corpus (23)

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• Oscillations excited by plasmoids formed during magnetic reconnection in vertical gravitationally stratified current-sheet
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• Impulsively generated wave trains in coronal structures: II. Effects of transverse structuring on sausage waves in pressureless slabs
• Fast sausage modes in magnetic tubes with continuous transverse profiles: effects of a finite plasma beta
• Quasi-periodic pulsations in a solar flare with an unusual phase shift
• Damping of slow surface sausage modes in photospheric waveguides
• Resonant Damping of Kink Modes in Solar Coronal Slabs
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• Possible Signature of Sausage Waves in Photospheric Bright Points
• Fast Standing Modes in Transversely Nonuniform Solar Coronal Slabs: Effects of a Finite Plasma Beta
• Non-equilibrium Ionization Effects on Extreme-Ultraviolet Emissions Modulated by Standing Sausage Modes in Coronal Loops
• Standing Sausage Perturbations in solar coronal loops with diffuse boundaries: An initial-value-problem perspective
• Impulsively Generated Kink Wave Trains in Solar Coronal Slabs
• Sensitivity of Coronal Loop Sausage Mode Frequencies and Decay Rates to Radial and Longitudinal Density Inhomogeneities: A Spectral Approach
• Fast Sausage Oscillations in Coronal Loops with Fine Structures
• Standing Sausage Perturbations in Solar Coronal Slabs with Continuous Transverse Density Profiles: cutoff wavenumbers, evanescent eigenmodes, and oscillatory continuum
• Transverse waves in coronal flux tubes with thick boundaries: The effect of longitudinal flows
• Oblique Quasi-Kink Modes in Solar Coronal Slabs Embedded in an Asymmetric Magnetic Environment: Resonant Damping, Phase and Group Diagrams
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