SDO/AIA Observations of a Reflecting Longitudinal Wave in a Coronal Loop

TL;DR

This paper reports high-resolution SDO/AIA observations of a hot coronal loop exhibiting a reflected longitudinal wave, consistent with slow magnetoacoustic waves, triggered by plasma ejection and rapid heating at a footpoint.

Contribution

It provides detailed observational evidence of a reflected slow magnetoacoustic wave in a hot coronal loop, linking impulsive heating to wave propagation and reflection.

Findings

Wave propagated along the loop with a speed matching the sound speed.

Wave reflected four times before fading.

Oscillation period and decay time measured at ~630s and ~440s.

Abstract

We report high resolution observations from the SDO/AIA of intensity oscillations in a hot, T~8-10 MK, loop. The AIA images show a large coronal loop that was rapidly heated following plasma ejection from one of the loop's footpoints. A wave-like intensity enhancement, seen very clearly in the 131 and 94 \AA\ channel images, propagated ahead of the ejecta along the loop, and was reflected at the opposite footpoint. The wave reflected four times before fading. It was only seen in the hot, 131 and 94 \AA\ channels. The characteristic period and the decay time of the oscillation was $\sim$630 and $\sim$440 s, respectively. The phase speed was about 460-510 km/s which roughly matches the sound speed of the loop (430-480 km/s). The observed properties of the oscillation are consistent with the observations of Doppler shift oscillations discovered by the SOHO/SUMER and with their interpretation as slow magnetoacoustic waves. We suggest that the impulsive injection of plasma, following reconnection at one of the loop footpoints, led to rapid heating and the propagation of a longitudinal compressive wave along the loop. The wave bounces back and forth a couple of times before fading.