Undersampling effects on observed periods of coronal oscillations

TL;DR

This study investigates how undersampling affects observed periods of decayless coronal oscillations, revealing that short loop oscillation periods may be overestimated due to sampling effects, explaining observed period-length relationships.

Contribution

It demonstrates that undersampling can produce the two observed period-length relationships, offering an explanation for the decayless oscillation period distributions.

Findings

Undersampling causes overestimation of short loop oscillation periods.

Two observed period-length relationships can result from sampling effects.

Long periods in short loops may be artifacts of undersampling.

Abstract

Context. Recent observations of decayless transverse oscillations have shown two branches in the relationship between periods and loop lengths. One is a linear relationship, interpreted as a standing mode. The other shows almost no correlation and has not yet been interpreted conclusively. Aims. We investigated the undersampling effect on observed periods of decayless oscillations. Methods. We considered oscillating coronal loops that closely follow the observed loop length distribution. Assuming that all oscillations are standing waves, we modeled a signal that represents decayless oscillations where the period is proportional to the loop length and the amplitude and phase are randomly drawn. A downsampled signal was generated from the original signal by considering different sample rates that mimic temporal cadences of telescopes, and periods for sampled signals were analysed using the fast Fourier transform. Results. When the sampling cadence is getting closer to the actual oscillation period, a tendency for overestimating periods in short loops is enhanced. The relationship between loop lengths and periods of the sampled signals shows the two branches as in the observation. Conclusions. We find that long periods of decayless oscillations occurring in short loops could be the result of undersampling.