The slow magnetoacoustic mode in the flaring loop

TL;DR

This study analyzes a solar flare using radio and X-ray observations, identifying quasi-periodic pulsations caused by the second standing harmonic of the slow magnetoacoustic mode, which may trigger repeated energy releases.

Contribution

It demonstrates that slow magnetoacoustic modes can be responsible for periodic pulsations in solar flares, linking observed oscillations to specific MHD wave modes.

Findings

Oscillation period grows from 2.5 to 5 minutes.

Quasi-periodic pulsations linked to the second standing harmonic.

Mode may trigger repeated energy releases.

Abstract

We studied long duration flare observed with Nobeyama Radioheliograph at frequencies 17 and 34 GHz and with Ramaty High Energy Solar Spectroscopic Imager at 25-50 keV. We found that microwave and hard X-ray emission variation contain well-pronounced periodicity with the oscillation period growing from 2.5 to 5 min. Analysis of the loop length and plasma temperature evolution during the flare allowed to interpret the quasi-periodic pulsations in terms of the second standing harmonics of the slow magnetoacoustic mode. This mode can be generated by the initial impulsive energy release and work as a trigger for the repeated energy releases.