Spectral Imaging of a Complex Zebra-pattern Radio Burst

Radio bursts with zebra patterns (hereafter ZP bursts) are the most intriguing coherent emission produced by nonthermal electrons, which have been recorded frequently on the dynamic spectrograms of the Sun, Jupiter, Saturn, and even supernova remnants. Solar decimetric ZP bursts, in particular, are thought to originate near flaring sites and can be used to diagnose the physical conditions and dynamic processes around the flaring sources, including magnetic fields, particle acceleration, plasma density, and instabilities. However, due to the lack of high-resolution imaging, their exact locations and formations remain a matter of controversy. This work provided, for the first time, a series of images of solar ZP bursts and tracked their morphology and evolution using high-cadence radio imaging spectroscopy. We found that (1) the ZP source region lies on the shoulder of a group of large-scale coronal loops connecting an active region with an M8.4 flare and a nearby active region, especially far from the flaring region and close to the nearby active region associated with a small-scale coronal jet and EUV brightening. (2) The ZP burst has a complex evolution that is modulated by a quasiperiodic pulsating process and gradually transitioned from the initial equidistant ZP to the frequency-growing ZP. We proposed that the ZP burst should be triggered by a small-scale magnetic reconnection associated with the small-scale jet in the nearby active region, as well as modulated by quasiperiodic pulsating MHD perturbations in the coronal loops.