LOFAR reveals spike-like repeating radio burst pairs in the solar corona

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The solar atmosphere is a turbulent and magnetized environment, with the release of magnetic energy readily manifesting as emission across the electromagnetic spectrum. Solar radio emission dominates the radio sky, with the brightest solar radio bursts generated via the plasma emission process. The emission has a complex frequency-time structure with many features that are yet to be understood.

Using the LOw Frequency ARray (LOFAR) radio telescope, researchers have detected "repeating spike-like burst pairs"—brief flashes of radio energy that occur in pairs, separated by a characteristic delay of about four seconds. The findings reveal a new diagnostic of turbulent plasma processes high above the sun's surface, providing a powerful tool for probing the sun's magnetic environment and particle acceleration.

The research is published in the journal Nature Communications.

Solar radio bursts are known to exhibit complex fine structures, but the newly discovered signals stand out. Each event consists of two nearly identical, narrowband radio spikes occurring at the same frequency: a short-lived "earlier" (E) burst followed by a weaker, delayed (D) "echo-like" burst approximately 4 seconds later.

In total, more than 600 such pairs were analyzed, revealing consistent patterns in their timing, intensity and spatial origin. By combining high-resolution spectroscopy with radio imaging, the team traced these bursts to an active region on the sun. The key breakthrough came from observing that the second burst in each pair originates from a different location in the corona—often displaced by hundreds of arcseconds.

The study suggests that these bursts originate at heights of around one solar radius above the surface, much higher than typical flare emission sites. This implies that magnetic reconnection and electron acceleration—key drivers of solar activity—may occur in previously underappreciated regions of the corona.

The bursts are likely produced when small-scale reconnection events accelerate electrons, generating plasma waves that emit radio signals. These signals then follow multiple paths through turbulent plasma, producing the delayed echo signature.

In summary, repeating spike-like burst pairs constitute a newly identified and abundant class of solar radio fine structure. Their defining characteristics—paired emission at identical frequency, separated by a ~4 s delay and sp