  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.
