Pulsations of microwave emission from a solar flare in a twisted loop caused by intrinsic MHD oscillations

TL;DR

This study models microwave pulsations in a twisted solar coronal loop caused by intrinsic MHD oscillations, revealing two distinct oscillation types with different periods and origins, explaining observed quasi-periodic pulsations.

Contribution

It demonstrates that intrinsic MHD oscillations in a twisted loop can produce observable microwave pulsations without external drivers, distinguishing two oscillation types and their physical mechanisms.

Findings

Longer-period oscillations (~70-75s) result from standing kink modes.

Shorter-period oscillations (~40s) are linked to energetic electron dynamics.

Oscillations can explain observed quasi-periodic pulsations in solar flares.

Abstract

We present results revealing microwave pulsations produced in a model of a flaring twisted solar coronal loop, without any external oscillatory driver. Two types of oscillations are identified: slowly-decaying oscillations with a period of about 70-75s and amplitude of about 5-10% seen in loops both with and without energetic electrons, and oscillations with period of about 40s and amplitude of a few tens of percent observed only in loops with energetic electrons for about 100s after onset of fast energy release. We interpret the longer-period oscillations as the result of a standing kink mode modulating the average magnetic field strength in the loop, whilst the short-period intermittent oscillations associated with energetic electrons are likely to be produced by fast variations of the electric field which produces energetic electrons in this scenario. The slowly-decaying oscillations can explain the quasi-periodic pulsations often observed in the flaring corona.