Microwave Imaging of Quasi-periodic Pulsations at Flare Current Sheet

TL;DR

This study observes microwave quasi-periodic pulsations during a solar flare, linking them to quasi-periodic magnetic reconnection and electron acceleration within the flare current sheet, supported by simulations.

Contribution

It provides observational evidence connecting microwave QPPs to magnetic reconnection modulation and validates this with magnetohydrodynamic simulations.

Findings

Microwave QPPs are associated with quasi-periodic reconnection.

Two microwave sources show in-phase brightness variations.

Simulations support modulation of magnetic islands as the cause.

Abstract

Quasi-periodic pulsations (QPPs) are frequently detected in solar and stellar flares, but the underlying physical mechanisms are still to be ascertained. Here, we show microwave QPPs during a solar flare originating from quasi-periodic magnetic reconnection at the flare current sheet. They appear as two vertically detached but closely related sources with the brighter ones located at flare loops and the weaker ones along the stretched current sheet. Although the brightness temperatures of the two microwave sources differ greatly, they vary in phase with periods of about 10--20 s and 30--60 s. The gyrosynchrotron-dominated microwave spectra also present a quasi-periodic soft-hard-soft evolution. These results suggest that relevant high-energy electrons are accelerated by quasi-periodic reconnection, likely arising from the modulation of magnetic islands within the current sheet as validated by a 2.5-dimensional magnetohydrodynamic simulation.