Astronomers tie record-long X-ray flash to a neutron star merger forming a magnetar

By the Everything Space news desk · 30 Sep 2026 · written from the sources below

Image: Phys.org

The finding could help reveal how often colliding neutron stars produce magnetars and may one day be matched with gravitational wave detections.

Astronomers have found evidence that a long-lasting X-ray flash detected in July 2025 came from the merger of two neutron stars, which appears to have created a magnetar rather than fading quickly like typical short gamma-ray bursts associated with such collisions.

The event, cataloged as EP250704a/GRB 250704B, was spotted by the SVOM, Insight-HXMT and Einstein Probe satellites. While its gamma-ray burst lasted only about half a second, the Einstein Probe recorded bright X-ray emission continuing for nearly ten minutes, making it the longest prompt X-ray flash yet linked to a neutron star merger.

Researchers led by professor Eleonora Troja quickly organized follow-up observations with the Very Large Telescope and the Very Large Array to study the aftermath. They suspect the merger produced a magnetar, an extremely magnetized, fast-spinning neutron star, whose energy release could explain the unusually long and bright X-ray signal.

Using the VLT's X-Shooter instrument, the team measured the burst's redshift at 0.6610, showing the light took more than six billion years to reach Earth, well before the solar system formed. Deep imaging with the VLT's FORS2 instrument found no accompanying supernova, ruling out the collapse of a massive star as the cause and strengthening the case for a neutron star merger.

The discovery suggests some unexplained fast X-ray transients detected since the Einstein Probe's 2024 launch may actually be signatures of neutron star mergers rather than dying massive stars. Researchers hope that identifying more such events could clarify how often these mergers create magnetars, and eventually allow scientists to match an X-ray flash with gravitational waves from the same collision.

Written in Everything Space’s own words by our news-desk model from the sources above, and checked against them in code: every number in this report appears in its sources, and no sentence is copied from them.