Soft X-rays kept flowing for about 560 seconds, or 9.3 minutes, after a gamma-ray burst that itself lasted well under a second. Einstein Probe, the X-ray observatory led by the Chinese Academy of Sciences, caught the signal on July 4, 2025, and a paper published in Science Bulletin in 2026 argues that such a long afterglow points to a newly formed, rapidly spinning magnetar.
The authors, led by An Li of Beijing Normal University, describe the event as an extended X-ray flash that follows the merger of two compact objects, most likely neutron stars. The magnetar is a hypothesis the data favor, not a confirmed discovery.
EP250704a and the burst that preceded it
The paper, titled “Minutes-long soft X-ray prompt emission from a compact object merger,” is on arXiv and carries the journal DOI 10.1016/j.scib.2026.08.021. It describes a “minutes-long (~560 s) flash of soft (0.5-4 keV) X-rays” immediately following GRB 250704B, a gamma-ray burst of about 0.4 seconds. The X-ray counterpart is named EP250704a.
The burst triggered at 08:16:27 UTC on July 4, 2025, according to the paper’s detailed preprint text, and was independently found by SVOM/GRM, Insight-HXMT and Konus-Wind. Einstein Probe’s Wide-field X-ray Telescope first saw X-rays a quarter of a second after the trigger, then triggered itself about 25 seconds in and slewed its Follow-up X-ray Telescope, which located a fading afterglow starting about 227 seconds after the burst.
Optical and radio follow-up put the burst at redshift 0.66102, based in part on a VLT X-shooter spectrum, and deep optical limits ruled out a bright supernova. Those two results place it among merger-driven bursts rather than the collapse of a massive star. The distance matters for the energy budget: at that redshift, the quoted soft X-ray luminosity of about 2.6 times 10 to the 47th ergs per second is a remarkable output to sustain for minutes, and it is the number any proposed engine has to supply.
Counting the 560 seconds
The length of the glow needs careful reading. The paper’s measured total in the 0.5 to 4 keV band is 561.91 seconds, with uncertainties of plus 67 and minus 100 seconds, which is about 9.3 minutes. The phrase “nearly ten minutes” comes from the Science China Press summary of the work, and it rounds that figure up; the paper itself uses the 560-second number.
The signal had three parts. An initial spike lasted about 0.35 seconds, a seconds-long tail followed, and then came an extended bump of roughly 540 seconds that began about 20 seconds after the trigger. The soft X-ray extended emission carried an isotropic energy of about 1.9 times 10 to the 50th ergs, against about 3.8 times 10 to the 51st ergs for the gamma-ray burst itself.
Earlier engine-driven models of such emission had discussed durations of about 100 seconds, so the roughly 560-second flash is several times longer than that benchmark. The authors argue that long-lasting soft X-ray emission may be common in merger-driven bursts and could serve as a counterpart to gravitational-wave sources.
Magnetar or black hole as the central engine
The central engine is the open question.
Yi-Han Iris Yin of the University of Hong Kong, one of the paper’s co-corresponding authors, said “One plausible explanation is that the merger produced a rapidly rotating, highly magnetized neutron star — known as a magnetar — that powered the extended X-ray emission and continued energy injection.” The other co-corresponding authors are Bin-Bin Zhang of Nanjing University and Eleonora Troja of the University of Rome Tor Vergata, and Bing Zhang is the last author.
The preprint attributes the extended bump to long-lasting, engine-powered emission and favors a long-lived magnetar, pointing to the sustained energy injection needed to explain the afterglow. It cites a shallow X-ray decay from about 690 seconds to 72,000 seconds and a slow optical rise between roughly 2,000 and 65,000 seconds. The abstract itself frames the central engine as either an accreting black hole or a neutron star.
The wording in the release is accordingly hedged: the long emission “could have been powered by a newly formed magnetar.” Einstein Probe, launched January 9, 2024 as a Chinese Academy of Sciences mission with ESA and the Max Planck Institute for Extraterrestrial Physics, carries lobster-eye optics that watch about 3,600 square degrees at once, which is how a faint, long X-ray glow like this one gets noticed at all. The satellite is built to catch X-ray emission from merging neutron stars and black holes, among other transients, according to the ESA factsheet, and EP250704a is a case of the telescope doing exactly that.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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