Plate Nº 88 · recorded October 10, 2026
Space & AstronomyReported finding
Record-Breaking X-Ray Flash May Mark Birth of a Magnetar
On July 4, 2025, three space telescopes caught a flash that blazed in X-rays for nearly ten minutes — the longest such signal ever linked to two colliding neutron stars and the possible birth of a magnetar.
By James Calloway4 min read746 words
In brief
- Event EP250704a/GRB 250704B was detected on July 4, 2025, and emitted X-rays for nearly ten minutes — a record for a neutron-star merger.
- The flash's light traveled more than 6 billion years to reach Earth, based on a measured redshift of z = 0.6610.
- Follow-up VLT observations found no associated supernova, ruling out a massive-star collapse.
- The study was published in Science Bulletin, 2026, 71 (18): 4657, DOI: 10.1016/j.scib.2026.08.021.
- Einstein Probe, launched in January 2024, has detected hundreds of fast X-ray transients with unclear origins.
On July 4, 2025, three space telescopes recorded a cosmic flash that blazed in X-rays for nearly ten minutes — the longest such signal ever linked to the merger of two neutron stars, according to a study published in Science Bulletin on September 30, 2026.
Astronomers have traditionally relied on short gamma-ray bursts, lasting less than two seconds, to identify these collisions. The new event, designated EP250704a/GRB 250704B, showed a gamma-ray signal of only about half a second. Its X-ray tail, however, kept shining long after the gamma rays faded.
"This is the longest lasting prompt X-ray flash ever observed from a neutron star merger," said Niccolò Passaleva, a graduate student at the University of Rome Tor Vergata who led the follow-up observations. "It is an opportunity to have a front-row seat to the most extreme forces of the Universe and discover more of its secrets."
What is a magnetar?
A magnetar is a neutron star — the ultra-dense remnant left behind when a massive star runs out of fuel — equipped with an extraordinarily strong magnetic field. If a merger leaves behind a magnetar rather than a black hole, that newborn object could keep pumping energy into its surroundings for minutes.
"However, if the remnant of the collision is a magnetar, it could keep bursting for longer," said Prof. Eleonora Troja of the University of Rome Tor Vergata, a co-corresponding author of the paper. "Magnetars are rapidly spinning neutron stars with huge magnetic fields. When they damp their magnetic power into the surroundings, they can make any explosion brighter and longer-lasting. When I saw the X-ray data from this new event, I realized something was up."
How was the flash caught?
The Einstein Probe satellite, launched in January 2024 as part of a European collaboration Troja belongs to, first flagged the event. Troja's team, supported by a European Research Council Consolidator Grant, then scrambled multiple ground- and space-based instruments to chase the afterglow.
Passaleva responded within minutes, using the European Southern Observatory's Very Large Telescope (VLT) in Chile. "I was traveling home by train," he recalls, "and all of a sudden I was rushing against time to commandeer one of the largest telescopes in the world from my laptop."
The team also turned to the Very Large Array in New Mexico. Two other satellites — SVOM and Insight-HXMT — confirmed the initial detection.
How far away was the explosion?
The VLT's X-Shooter instrument split the flash's light into a spectrum. Distinct absorption lines yielded a redshift of z = 0.6610. That figure means the light left its source more than six billion years ago, well before our Sun and its planets formed.
What rules out other explanations?
Fast X-ray transients, or FXTs, can also come from the collapse of massive stars. The team therefore searched for the bright supernova that would normally follow such a death, using deep VLT observations with the FORS2 instrument.
No supernova appeared.
The combination of distance, missing supernova, and burst properties pointed strongly to a neutron-star merger.
What changes now?
Since Einstein Probe began operating, it has detected hundreds of bright X-ray flashes whose origins remain uncertain. Linking one of them to a neutron-star merger gives astronomers a fresh way to find these extreme collisions — and to test how often they leave behind magnetars.
"Finding more of these X-ray flashes could help reveal how often neutron star mergers create magnetars," Passaleva said. "I am really excited for the next run of gravitational wave observations, when we could finally pair one of these X-ray flashes with a burst of gravitational waves from the same source."
Caveats to keep in mind
The conclusion rests on a single event. Astronomers still need more examples to confirm that long X-ray tails reliably signal magnetar births. The next observing run of gravitational-wave detectors could supply independent confirmation by registering the underlying merger directly.
The international collaboration includes researchers from Beijing Normal University, the Chinese Academy of Sciences, the University of Rome Tor Vergata, Nanjing University, the University of Hong Kong, and many other institutions. Lead authors are An Li, Chen-Wei Wang, Niccolò Passaleva and Jie An. Corresponding authors include Binbin Zhang, Eleonora Troja, Yi-Han Iris Yin, Jing-Wei Hu and Hua-Li Li. The VLT campaign ran under the program "QUEENB: a QUEst for Elusive Neutron star and Black hole mergers."
via dx.doi.org (Original)
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