An international team of astronomers has linked a nearly ten-minute X-ray flash to a gamma-ray burst that lasted about 0.4 seconds, offering evidence that some collisions involving compact stars remain active much longer than their initial burst suggests. The finding appeared in Science Bulletin on September 30, according to the University of Hong Kong, whose researchers contributed to the analysis.
The event was detected on July 4, 2025, and is known as EP250704a in X-rays and GRB 250704B in gamma rays. Short gamma-ray bursts are commonly associated with mergers of compact objects, including neutron stars. Such bursts have usually been studied through their brief gamma-ray emission, while telescopes pointed at them later could miss the earliest, softer X-rays.
The China-led Einstein Probe monitored the source in soft X-rays from its onset. The Space Variable Objects Monitor and Insight-HXMT detected the gamma-ray burst. Researchers also used follow-up observations from ground-based facilities, including the European Southern Observatory's Very Large Telescope, to investigate the source and its distance.
The team's analysis found that the X-ray signal continued for about 560 seconds after the brief gamma-ray flash. Its changing spectrum and rapid variations did not fit a simple account in which a burst is followed only by a conventional afterglow. The authors instead interpret the long X-ray phase as continued energy release from the central engine of a compact-object merger.
The researchers say a rapidly spinning, strongly magnetized neutron star, or magnetar, is one possible source of that continued power. They have not established that this was the remnant in this event. The observations also do not show that every short gamma-ray burst has the same prolonged X-ray phase; other examples will be needed to test how often it occurs.
The study suggests that wide-field soft X-ray monitoring could reveal mergers missed or incompletely described by gamma-ray instruments. That would give astronomers another signal to compare with future gravitational-wave detections and help them investigate what happens immediately after compact stars collide. The team expects further observations to test the proposed link.
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