In the vast cosmos, fast radio bursts (FRBs) remain one of the most mysterious astrophysical phenomena ever discovered. These intense, millisecond-duration radio pulses can release in the radio band alone as much energy as the Sun emits in a day—or even a year. Yet, their origin is still unclear. 

Recently, Dr. BAI Juntao , a PhD student at the Xinjiang Astronomical Observatory (XAO) of the Chinese Academy of Sciences (CAS), under the guidance  of Prof. WANG Na, led a collaborative study involving researchers from Guangzhou University, Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia, and the Purple Mountain Observatory of CAS. The team conducted deep radio observations of eight pulsing ultraluminous X-ray sources (PULXs) using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China and the Parkes radio telescope (Murriyang) in Australia, searching for potential FRB-like emission from these extreme systems.

The results were published in The Astrophysical Journal (ApJ, 2025, 984, 33).

PULXs are a class of neutron star-powered ultraluminous X-ray sources whose X-ray luminosities significantly exceed the Eddington limit, indicating the presence of super-Eddington accretion processes. In such extreme physical conditions—especially during energetic accretion outbursts—some models suggest that these systems may be capable of producing FRBs.

To test this hypothesis, the team conducted high-sensitivity radio observations of eight PULXs,  covering a wide range of orbital phases. They employed both single-pulse and periodicity search techniques, scanning dispersion measures from 0 to 5000 pc cm⁻³. Ultimately, no significant radio pulses were detected from any of the targets.

This result suggests that if FRB-like activity occurs in PULX systems, it is likely to be extremely rare, or the radio signals may be absorbed or scattered by strong accretion-driven winds, dense magnetized environments, or simply beamed away from Earth. The team also derived stringent upper limits on the radio flux density of each source (see Figure 1), placing strong observational constraints on current PULX–FRB theoretical models.

This study represents the first dedicated FRB search focused on PULX systems, providing valuable observational evidence to assess the possibility of FRB generation in compact binaries. In addition, it places meaningful constraints on the increasingly discussed "binary-origin" hypothesis for FRBs and  expands the observational frontier in the search for FRB progenitors.

The study was supported by the National Natural Science Foundation of China and the National Key R&D Program of China.

                                                                                                                Figure 1 The flux density width parameter space.

Article link: https://iopscience.iop.org/article/10.3847/1538-4357/adc92e/pdf