Astronomers may have witnessed the birth of a magnetar after two neutron stars collided, following the detection of an unusually long-lasting X-ray flash.
The event, designated EP250704a/GRB 250704B, was detected on July 4, 2025, by the SVOM, Insight-HXMT and Einstein Probe satellites. While its gamma-ray burst lasted only about half a second, Einstein Probe detected bright X-ray emission for nearly 10 minutes.
A study published in Science Bulletin found evidence supporting a neutron star merger as the source of the event. Astronomers have traditionally used short gamma-ray bursts, which can disappear in less than two seconds, to identify such collisions.
Researchers from Professor Eleonora Troja’s group quickly followed the event using several instruments, including the European Southern Observatory’s Very Large Telescope (VLT) and the Very Large Array. With the VLT’s X-Shooter instrument, they measured a redshift of 0.6610, indicating that the event occurred billions of years ago, long before the formation of the Sun and its planets. Its light took more than six billion years to reach Earth.
The team also searched for a supernova, which would be expected if the X-ray flash had instead resulted from the collapse of a massive star. No supernova was detected.
The researchers say the event’s distance, lack of a supernova and unusually long X-ray emission strongly support a neutron star merger and possible magnetar formation. Further events could help determine how often such mergers produce magnetars.
