Spatiotemporal Analysis of Coronal Loops Using Seismology of Damped Kink Oscillations and Forward Modeling of EUV Intensity Profiles

Abstract

The shape of the damping profile of kink oscillations in coronal loops has recently allowed the transverse density profile of the loop to be estimated. This requires accurate measurement of the damping profile that can distinguish the Gaussian and exponential damping regimes, otherwise there are more unknowns than observables. Forward modeling of the transverse intensity profile may also be used to estimate the width of the inhomogeneous layer of a loop, providing an independent estimate of one of these unknowns. We analyze an oscillating loop for which the seismological determination of the transverse structure is inconclusive except when supplemented by additional spatial information from the transverse intensity profile. Our temporal analysis describes the motion of a coronal loop as a kink oscillation damped by resonant absorption, and our spatial analysis is based on forward modeling the transverse EUV intensity profile of the loop under the isothermal and optically thin approximations. We use Bayesian analysis and Markov chain Monte Carlo sampling to apply our spatial and temporal models both individually and simultaneously to our data and compare the results with numerical simulations. Combining the two methods allows both the inhomogeneous layer width and density contrast to be calculated, which is not possible for the same data when each method is applied individually. We demonstrate that the assumption of an exponential damping profile leads to a significantly larger error in the inferred density contrast ratio compared with a Gaussian damping profile.

Coronal Loop Seismology Using Standing Kink Oscillations With a Lookup Table

“…It is possible to apply both of these methods simultaneously to observational data. This was recently demonstrated by Pascoe et al (2018) for a loop for which the oscillation data alone was too noisy to allow strong constraint of ζ and ǫ. However, the spatial information from the intensity profile produced a strong constraint on ǫ, such that the oscillation data was only required to infer ζ when both methods were applied simultaneously.…”

Evolution of the Transverse Density Structure of Oscillating Coronal Loops Inferred by Forward Modeling of EUV Intensity

“…Model L (the linear transition layer model) for the density profile will be used, as given in Equation 1. Pascoe et al (2018) considered seven different transverse density profiles which have been used to describe coronal loops and demonstrated that the linear transition layer profile described the widest range of possible structures, being able to approximate homogeneous, partially inhomogeneous and completely inhomogeneous density profiles. The loop in the numerical modelling was not isothermal, and as such the cooler core is well seen at 171 Å channel, and the hot boundary is better seen in a hotter channel.…”

“…This study indicated that loops may have thicker boundary layers than is typically assumed, or even constantly varying TDPs, subject to the limitations and simplifications discussed. Additionally in Pascoe et al (2018) this technique was applied to an oscillating coronal loop to infer the time evolution of the density profile model parameters.…”

No unique solution to the seismological problem of standing kink magnetohydrodynamic waves

“…Additional information can be extracted from the EUV transverse intensity profile observed by EUV imagers such as SDO/AIA. For a particular event, Pascoe et al (2018) found that linear and sinusoidal models are the most consistent with the observed EUV intensity profile. Synthetic and observed EUV profiles could be incorporated into a Bayesian analysis to obtain further information.…”