Plate Nº 52 · recorded October 10, 2026
Space & AstronomyReported finding
Einstein Probe catches 10-minute X-ray tail of neutron star merger
Einstein Probe detected nearly 10 minutes of soft X-ray emission following a 0.4-second gamma-ray burst likely caused by a neutron star merger, revealing a previously hidden phase of high-energy activity.
By Nathan Brooks4 min read892 words
In brief
- Gamma-ray burst GRB 250704B lasted about 0.4 seconds; soft X-ray emission from EP250704a continued for nearly 10 minutes.
- Einstein Probe, SVOM and Insight-HXMT jointly detected the event on or around July 4, 2025.
- A possible explanation for the lingering X-rays is a newborn magnetar, a rapidly spinning, highly magnetized neutron star.
- The study appears as a cover article in Science Bulletin in 2026 (DOI: 10.1016/j.scib.2026.08.021).
- HKU Ph.D. student Yi-Han Iris Yin served as co-corresponding author alongside researchers from Beijing Normal University and Nanjing University.
The Einstein Probe captured nearly 10 minutes of soft X-ray emission following a gamma-ray burst that lasted only about 0.4 seconds, revealing a previously hidden phase of high-energy activity after what astronomers believe was the merger of two compact stars. The event, catalogued as EP250704a in X-rays and GRB 250704B in gamma rays, appears on the cover of Science Bulletin. An international team led by An Li of Beijing Normal University and Bin-Bin Zhang of Nanjing University reports the result.
What did the telescopes actually see?
Three space missions caught the burst from different angles. China's Einstein Probe (EP) spotted the event from the start with its wide-field X-ray telescope. The France-China mission SVOM and China's Insight-HXMT simultaneously recorded the gamma-ray flash.
The gamma-ray signal died after roughly 0.4 seconds. But EP kept watching. It logged several episodes of soft X-ray emission that stretched to almost 10 minutes. That extended tail would not have shown up in any gamma-ray detector's record.
Why had this phase been hidden until now?
Short gamma-ray bursts usually mark collisions between compact objects, two neutron stars, or a neutron star paired with a black hole. Most X-ray telescopes only swing into action after a gamma-ray detector alerts them. By the time they begin recording, the earliest X-rays have often faded.
Einstein Probe works differently. It continuously sweeps a wide area of sky at soft X-ray energies, so it caught EP250704a from the very first moments and stayed on target. Yi-Han Iris Yin, a Ph.D. student at the University of Hong Kong (HKU) and co-corresponding author of the study, led the analysis of the high-energy prompt emission.
Her analysis highlighted four key points:
- The X-ray source stayed active for nearly 10 minutes after the gamma-ray flash ended.
- The X-rays' rapid flicker and shifting energy signature indicate a still-spinning central engine.
- One likely explanation is a magnetar, a neutron star that spins rapidly and carries an extraordinarily strong magnetic field.
- Similar soft X-ray tails may exist in older short gamma-ray bursts but went unseen because the signals were too soft and faint for gamma-ray instruments to register.
What is a magnetar, and could it power the glow?
A magnetar is a rare and extreme type of neutron star, a stellar remnant that spins rapidly and carries a magnetic field so strong it can warp the surrounding space. After a neutron-star merger, a newborn magnetar could keep feeding energy into the surrounding debris, producing the soft X-rays EP detected.
The data do not yet confirm the magnetar scenario outright. The rapid variability and evolving spectrum are consistent with continued central-engine activity, but other explanations remain possible. The team calls the result preliminary and notes that more events are needed to settle the question.
What could this change for future detections?
If prolonged soft X-ray tails are common after compact-object mergers, they could give astronomers a second channel for spotting events that current gamma-ray satellites miss. They could also complement gravitational-wave detectors by offering a longer, more detailed light signal from the same mergers.
The authors also suggest that similar emissions may have been hiding in archival short gamma-ray bursts, masked by instruments tuned to harder energies.
Who is behind the work, and why does it matter?
The study brought together HKU, Nanjing University, the University of Rome "Tor Vergata," the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), the Institute of High Energy Physics of the Chinese Academy of Sciences, and several other institutions. Co-first authors include BNU's Li and researchers from the Institute of High Energy Physics, the University of Rome "Sapienza," and the University of Chinese Academy of Sciences. Corresponding authors include NJU's Bin-Bin Zhang, Eleonora Troja from Tor Vergata, and HKU's Yin.
Bing Zhang, founding director of HKU's Hong Kong Institute for Astronomy and Astrophysics (HKIAA), co-authored the paper. He has long argued that binary neutron star mergers could produce fast X-ray transients visible to missions such as Einstein Probe. He used the occasion to spotlight his student's role.
"One of our goals at HKIAA is to create an environment where talented young researchers can take on scientific leadership and work at the forefront of international astronomy," Zhang said. "It is particularly encouraging to see our Ph.D. student Yin taking a leading role as one of the corresponding authors in this international collaboration."
Yin framed the broader scientific message.
"Einstein Probe is allowing us to uncover a part of compact star mergers that was hidden from previous gamma-ray observations," Yin said. "The short gamma-ray flash may represent only the beginning of the high-energy activity. By observing the universe at soft X-ray energies, we can now follow these systems for much longer and obtain a more complete view of what happens during and after the merger."
The paper, "Minutes-long soft X-ray prompt emission from a compact object merger" (DOI: 10.1016/j.scib.2026.08.021), adds weight to a long-running bet that X-ray surveys could reshape how astronomers track the universe's most violent collisions.
via Phys.org Space & Astronomy (Source)
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