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A short gamma-ray burst detected on July 4, 2025, lasted about 0.4 seconds. Then a space telescope recorded soft X-ray emission from the same event for roughly 560 seconds—about nine minutes. The X-rays were not a gamma-ray signal that kept going: they were a separate, lower-energy phase that offers clues to what happened after a compact-object merger.
What happened after the gamma-ray burst?
The event is known as GRB 250704B in gamma rays and EP250704a for its X-ray transient. An Li and collaborators report that the gamma-ray burst began at 08:16:27.10 UTC on July 4, 2025, and had a measured T90 duration of 0.37 ± 0.06 seconds. T90 is the interval in which a burst’s central 90% of measured gamma-ray emission arrives.
Starting about 0.2 seconds after the gamma-ray trigger, the Einstein Probe wide-field X-ray telescope detected a multi-episode flash in the 0.5–4 keV soft X-ray band. That emission lasted approximately 560 seconds. The study, “Minutes-long soft X-ray prompt emission from a compact object merger,” appeared in Science Bulletin in 2026 (paper record).
| Phase | What was observed | Duration |
|---|---|---|
| Short gamma-ray burst | GRB 250704B; detected by SVOM/GRM, Insight-HXMT, and Konus-Wind, among other observations reported in the study | T90 = 0.37 ± 0.06 seconds |
| Soft X-ray transient | EP250704a; detected by Einstein Probe in the 0.5–4 keV band | About 560 seconds |
“Ten minutes” is a rounded description of the X-ray phase, not the duration of the gamma-ray burst. A gamma-ray burst is the brief, powerful high-energy flash; an afterglow is lower-energy radiation that can follow it. NASA describes this distinction in its gamma-ray burst glossary. In this event, the observed soft X-ray activity was unusually long and its variability and spectrum led the authors to interpret it as a distinct phase of prompt X-ray emission, rather than simply treating it as a standard afterglow.
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Why did the X-rays last longer than the gamma rays?
The observation establishes that the emission changed in both energy and duration: the hard gamma-ray flash faded quickly, while lower-energy X-rays arrived in episodes for minutes. The measurements do not, by themselves, identify the exact engine that powered those episodes. The paper’s authors argue that the signal’s variability and spectral shape do not fit the canonical picture of a hard, accretion-powered spike followed by a standard external-shock afterglow.
Instead, they interpret the X-rays as evidence that the central engine remained active after a compact-object merger. Their multiwavelength afterglow observations and stringent limits on an associated supernova support that interpretation. It is a physical explanation of the observations, not a direct view of the merger remnant.
Could the merger have left a magnetar?
One plausible explanation is that the merger produced a magnetar: a rapidly rotating, highly magnetized neutron star that continued to inject energy and power the extended X-rays. The study’s co-corresponding author Yi-Han Iris Yin described this as “one plausible explanation.” The remnant has not been conclusively identified as a magnetar.
Why did Einstein Probe matter?
The X-ray component was detected because Einstein Probe monitored the event at soft X-ray energies with wide-field coverage. The paper says the extended component would not have been detected without this coverage. Instruments that register the brief gamma-ray flash but lack comparable soft X-ray observations could therefore miss this longer phase.
That makes the event important beyond its unusual duration: it suggests that extended soft X-ray activity may occur in merger-driven bursts more often than past observations revealed. The authors present that as an implication, not a settled measurement of how common such flashes are. A background statistic about engine-driven X-ray emission in short bursts should not be mistaken for a measured prevalence of confirmed prompt soft X-ray flashes.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Does this mean gravitational waves were detected?
No. The study links the electromagnetic observations to a compact-object merger, but it does not report a gravitational-wave detection from GRB 250704B. Events like this are promising electromagnetic counterparts for future gravitational-wave observations: coordinated signals could help researchers connect a merger seen through gravitational waves with radiation observed across the spectrum.
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What the observation tells us—and what it does not
- Measured: a gamma-ray burst with T90 of 0.37 ± 0.06 seconds, followed almost immediately by soft X-ray activity lasting about 560 seconds.
- Interpretation: the X-ray behavior supports prolonged central-engine activity after a compact-object merger.
- Not established: that a magnetar was definitively formed, or that gravitational waves were detected from this event.
- Broader implication: sensitive soft X-ray monitoring may reveal extended emission that observations focused on the initial gamma-ray flash miss.
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