Comparison of damping models for kink oscillations of coronal loops

Abstract

Kink oscillations of solar coronal loops are of intense interest due to their potential for diagnosing plasma parameters in the corona. The accurate measurement of the kink oscillation damping time is crucial for precise seismological diagnostics, such as the transverse density profile, and for the determination of the damping mechanism. Previous studies of large-amplitude rapidly-decaying kink oscillations have shown that both an exponential damping model and a generalised model (consisting of Gaussian and exponential damping patterns) fit observed damping profiles sufficiently well. However, it has recently been shown theoretically that the transition from the decaying regime to the decayless regime could be characterised by a super-exponential damping model. In this work, we re-analyse a sample of decaying kink oscillation events, and utilise the Markov Chain Monte Carlo Bayesian approach to compare the exponential, Gaussian–exponential and super-exponential damping models. It is found that in seven out of ten analysed oscillations, the preferential damping model is the super-exponential one. In two events, the preferential damping is exponential, and in one it is Gaussian–exponential. This finding indicates the plausibility of the super-exponential damping model. The possibility of a non-exponential damping pattern needs to be taken into account in the analysis of a larger number of events, especially in the estimation of the damping time and its associated empirical scalings with the oscillation period and amplitude, and in seismological inversions.