Quasi-periodic pulsations driven by structural oscillations in a kink-unstable flaring coronal loop

ABSTRACT Twisted coronal loops in the solar atmosphere may become kink unstable when their magnetic field lines are sufficiently twisted. This instability can trigger magnetic reconnection, leading to the emission of electromagnetic radiation, which manifests as a solar flare. Previous research has demonstrated that oscillations in microwave emissions, resembling observed quasi-periodic pulsations, can be generated by the reconnecting loop. Our aim is to investigate the relationship between the oscillations of the loop and these microwave pulsations. Using 3D magnetohydrodynamical simulations, we examine two models: a straight loop in a uniform-density atmosphere and a curved loop in a gravitationally stratified atmosphere. Using a new methodology, we extract the reconnecting loop-top from both models and identify structural oscillations. We then compare these oscillations with the gyrosynchrotron (GS) radiation emitted from the simulations, which is forward modelled using a radiative transfer code. We find that oscillations in the GS emissions are driven by sausage- and kink-mode oscillations. However, the relationship between the oscillation frequencies of the GS emission and the identified loop oscillation modes is complex. The dominant mode in the former may result from interference between sausage-mode and kink-mode oscillations or entirely different mechanisms. Results such as these increase our understanding of the time-dependent behaviour of solar flares and lay the groundwork for potential diagnostic tools that could be used to determine physical parameters within a flaring loop.