China’s Einstein Probe satellite has captured the longest-lasting prompt X-ray flash ever seen from a neutron star merger.

The event, named EP250704a and GRB 250704B, began on July 4, 2025. A gamma-ray burst flashed for less than half a second, just 0.37 seconds.

Instead of fading, the source kept emitting soft X-rays for nearly ten minutes. The total X-ray glow lasted about 562 seconds.

The findings were published in Science Bulletin. An Li, a PhD student at Beijing Normal University and the mission’s transient advocate, was on shift when the alert arrived.

Most X-ray telescopes missed such phases in the past. They have narrow fields of view and must wait for a gamma-ray alert before turning to the target. By then, the softest X-rays had passed.

Einstein Probe watches a wide area of sky in soft X-rays. It caught the explosion as it unfolded. The discovery may help scientists understand the central engines that drive these cosmic collisions.