The most sensitive search to date for a persistent radio source associated with an extremely bright, non-repeating fast radio burst (FRB) has yielded no detection, a result that significantly narrows the range of possible explanations for these mysterious cosmic phenomena.

A joint research team from the Shanghai Astronomical Observatory of Chinese Academy of Sciences, and the University of Science and Technology of China used the Very Large Array to search for potential persistentradio emissionfrom FRB 20250316A, one of the brightest non-repeating bursts ever detected. The results, published in The Astrophysical Journal Letters, provide a stringent upper limit yet on persistent radio emission from a non-repeating FRBs.

Fast Radio Burstsare among the most energetic phenomena in the Universe, releasing as much energy in milliseconds as the Sun produces in days. Since their discovery over a decade ago, astronomers have identified two distinct classes: repeating bursts that flash multiple times from the same location, and non-repeating bursts that appear only once. A key question has been whether these different types arise from fundamentally different physical processes.One major clue lies in whether FRB sources are associated with persistent radio emission between bursts. Some repeating FRBs show such persistent sources, potentially indicating ongoing activity in their local environment. However, for non-repeating FRBs, this question has remained largely unanswered due to the extreme sensitivity required for detection.

FRB 20250316A provided an ideal test case. The burst was both exceptionally bright and relatively nearby, making it possible to search for even the faintest persistent emission. Using observations taken within one month after the burst, the team achieved unprecedented sensitivity, thus setting an upper limit of 2.8 microJansky (1 sigma) at 15 GHz, consistent with independent observations by the Canadian Hydrogen Intensity Mapping Experiment(CHIME) Collaboration at 9.9 GHz about two months postburst.

"This non-detection is actually an interesting result," said Prof. AN Tao, the first author, "We can now rule out several theoretical models that predict bright, persistent radio sources around non-repeating FRBs. The environment appears much 'cleaner' than some theories suggested."

Specificly, the finding eliminates magnetar-nebula models,a leading explanation for some repeating FRBs,as a viable option for this non-repeating burst. Instead, the results favor scenarios such as neutron star mergers or giant flares from more evolved, isolated magnetars, which occur in low-density environments unlikely to produce long-lasting radio emission.

This work represents a crucial step toward understanding whether repeating and non-repeating FRBs arise from distinct physical mechanisms, a question that has important implications for our understanding of extreme physics in the Universe.As larger samples of FRBs are discovered and studied with increasing precision, astronomers are moving closer to solving one of modern astrophysics' most intriguing puzzles.

Figure: Very Large Array (VLA) images show that no persistent radio source was detected at the position of FRB 20250316A across different frequency bands and observation periods.

This work was supported by the National Key R&D Program SKA Project, the National Natural Science Foundation of China, the Strategic Priority Research Program of the Chinese Academy of Sciences, the Shanghai Oriental Talent Leadership Program, the Tianchi Program of Xinjiang Uygur Autonomous Region, and the China Postdoctoral Science Foundation. Data processing was completed at the China node of the SKA Regional Centre.

Contact Information: AN Tao antao@shao.ac.cn

Paper link:https://doi.org/10.3847/2041-8213/ae0324