Abstract
Coronal loops exist ubiquitously in the solar atmosphere. These loops puzzle astronomers over half a century. Solar magneto-seismology (SMS) provides a unique way to constrain the physical parameters of coronal loops. Here, we study the evolution of oscillations of a coronal loop observed by the Atmospheric Imaging Assembly (AIA). We measure geometric and physical parameters of the loop oscillations. In particular, we find that the mean period of the oscillations increased from 1048 to 1264 s during three oscillatory cycles. We employ the differential emission measure method and apply the tools of SMS. The evolution of densities inside and outside the loop is analyzed. We found that an increase of density inside the loop and decrease of the magnetic field strength along the loop are the main reasons for the increase in the period during the oscillations. Besides, we also found that the amplitude profile of the loop is different from a profile would it be a homogeneous loop. It is proposed that the distribution of magnetic strength along the loop rather than density stratification is responsible for this deviation. The variation in period and distribution of amplitude provide, in terms of SMS, a new and unprecedented insight into coronal loop diagnostics.
Highlights
Coronal loop kink oscillations can be triggered directly by e.g. flares, EUV waves, or indirectly by, e.g., coupling through excitation of Alfvén waves at the loop footpoint[17,18,19]
Besides solar magneto-seismology (SMS), a combination of magnetic field extrapolation and differential emission measure (DEM) methods are employed here to diagnose these physical parameters of oscillating loops
The ratio of the inside and outside density of a loop can be determined by SMS and the DEM methods independently, and the strength of magnetic field, B, can be determined by SMS and magnetic field extrapolation independently
Summary
Coronal loop kink oscillations can be triggered directly by e.g. flares, EUV waves, or indirectly by, e.g., coupling through excitation of Alfvén waves at the loop footpoint[17,18,19]. X (arcsecs) strength can be obtained from measuring the periods of the kink oscillations[34] Based on this approach, called solar magneto-seismology (SMS), studies have been carried out to infer the magnetic field of coronal loops from the observed periods of kink oscillations[5,36]. Besides the important information about magnetic field strength, another crucially needed input for constraining the theoretical approach, e.g. ratio of the inside and outside densities of a coronal loop can be estimated by the SMS35. This density ratio can be estimated by applying the differential emission measure (DEM) method[2]. We report the spatial distribution of the amplitude of the fundamental kink oscillation, in order to carry out spatio-magneto-seismology[38,39,40]
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