First detection of transverse vertical oscillation during the expansion of coronal loops

TL;DR

This study reports the first observation of transverse vertical oscillation of coronal loops during the expansion phase of a solar flare, revealing new insights into flare-loop interactions and coronal dynamics.

Contribution

It introduces a novel observation of transverse vertical oscillation during coronal loop expansion and proposes a unified scenario explaining both contraction and expansion phenomena.

Findings

EUV wave propagates at 740-860 km/s, indicating a fast-mode shock.

Oscillation periods of 253 s and 275 s observed in different wavelengths.

Interaction between EUV wave and coronal loops causes contraction, expansion, and oscillation.

Abstract

In this Letter, we perform a detailed analysis of the M5.5-class eruptive flare occurring in active region 12929 on 2022 January 20. The eruption of a hot channel generates a fast coronal mass ejection (CME) and a dome-shaped extreme-ultraviolet (EUV) wave at speeds of 740$-$860 km s$^{-1}$. The CME is associated with a type II radio burst, implying that the EUV wave is a fast-mode shock wave. During the impulsive phase, the flare shows quasi-periodic pulsations (QPPs) in EUV, hard X-ray, and radio wavelengths. The periods of QPPs range from 18 s to 113 s, indicating that flare energy is released and nonthermal electrons are accelerated intermittently with multiple time scales. The interaction between the EUV wave and low-lying adjacent coronal loops (ACLs) results in contraction, expansion, and transverse vertical oscillation of ACLs. The speed of contraction in 171, 193, and 211 {\AA} is higher than that in 304 {\AA}. The periods of oscillation are 253 s and 275 s in 304 {\AA} and 171 {\AA}, respectively. A new scenario is proposed to explain the interaction. The equation that interprets the contraction and oscillation of the overlying coronal loops above a flare core can also interpret the expansion and oscillation of ACLs, suggesting that the two phenomena are the same in essence.