Gamma rays from the explosion lasted roughly a third of a second. The X-rays kept going for what the research team calls nearly ten minutes, the longest prompt X-ray flash yet seen from a merger of two neutron stars, according to graduate student Niccolo Passaleva, one of the authors.
The team argues the lingering glow is the signature of a newborn magnetar, an ultra-magnetized neutron star, left behind when the two stars collided more than six billion years ago. That reading is their interpretation of the data, and they describe the evidence as strong rather than conclusive.
Nearly ten minutes after a half-second burst
The event is cataloged as EP250704a for its X-ray signal and GRB 250704B for its gamma-ray burst. The Einstein Probe’s Wide-field X-ray Telescope triggered at 08:16:52 UTC on July 4, 2025, according to NASA’s General Coordinates Network, in step with a short gamma-ray burst picked up by the SVOM satellite. The announcement of the study came on September 30, 2026, roughly 15 months after the flash, which gave the team time to gather radio, optical and X-ray afterglow data, work through the spectra and put the interpretation through peer review at Science Bulletin. Radio, X-ray and optical afterglows were all detected, and the optical light curve behaved unusually, staying flat or rising for roughly the first 16 hours before fading quickly, according to the GCN circulars.
The duration needs a careful reading. The research announcement says the Einstein Probe recorded X-ray emission for nearly ten minutes. The team’s preprint, led by An Li and Chen-Wei Wang and accepted by the journal Science Bulletin, puts it at about 560 seconds, which is roughly nine minutes and twenty seconds, and measures the gamma-ray burst itself at 0.37 seconds. The arXiv paper calls the X-ray flash minutes-long and describes it as the first direct observation of a prompt soft X-ray component from a compact object merger.
The Einstein Probe is a Chinese Academy of Sciences mission with partners at the European Space Agency and the Max Planck Institute for Extraterrestrial Physics, launched in January 2024. Its wide-field X-ray telescope uses a lobster-eye optical design to survey nearly one-tenth of the sky at once, which is why it could catch a soft X-ray glow that gamma-ray-focused instruments would likely have missed, as the Max Planck Society’s mission summary describes the instrument.
The case for a newborn magnetar
The puzzle is how a collision could keep an X-ray engine running for minutes. The team’s answer is that the merger left a rapidly rotating, strongly magnetized neutron star rather than a black hole. According to the paper, three observations favor an internal engine: variability too rapid for standard afterglow models, spectral hardening that marks the handoff from prompt emission to afterglow, and time dependence resembling the plateaus seen in other short bursts.
A collapsing massive star is the usual rival explanation for long-lasting gamma-ray and X-ray transients, and the team’s observations argue against it. Observations with the Very Large Telescope’s X-Shooter and FORS2 instruments measured a redshift of 0.661, placing the event about six billion years back in time, and found no associated supernova. The absence of a supernova points toward a merger, which is the setting in which magnetars are theorized to form. Professor Eleonora Troja’s group, supported by a European Research Council grant, coordinated the rapid follow-up across observatories.
An independent group reached a similar conclusion by a different route. A separate paper by Nissim Fraija and colleagues, titled a short gamma-ray burst powered by a magnetar, models the same event and says the remnant is most likely a long-lived magnetar, though it analyzes the X-ray emission over nearly two days rather than the first minutes.
One Einstein Probe event, one unproven magnetar
The preprint is open about the limits. It says the physical origin of similar extended emission seen earlier by the Chandra telescope remains unsettled, and the expected kilonova, the glow of radioactive debris from a merger, could not be detected at this distance. One event cannot say how often neutron star mergers leave magnetars behind, so the magnetar remains one possible explanation for the measurements rather than a proven one. Passaleva’s description of the flash as the longest of its kind is a statement about a record, not a verdict on what powered it.
The authors argue the signal is probably common: the preprint says long-lasting X-ray emission is likely a feature of merger-driven bursts, and finding more of them could show how often mergers leave magnetars and allow X-ray observations to be paired with gravitational-wave detections. That test depends on the Einstein Probe catching another burst this early and this faintly, which is the part the single July 2025 event cannot settle.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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