Researchers identified a 10-minute soft X-ray emission following a short gamma-ray burst, revealing a previously hidden phase of activity in compact object mergers.

An international team of astronomers has discovered a prolonged phase of high-energy activity after a compact star merger. The event, designated EP250704a in X-rays and GRB 250704B in gamma rays, was captured by the Einstein Probe, the Space Variable Objects Monitor, and the Insight-Hard X-ray Modulation Telescope. While the initial gamma-ray burst lasted only 0.4 seconds, the source continued to emit soft X-rays for nearly 10 minutes.

New Insights from Einstein Probe

The Einstein Probe's ability to continuously monitor a wide area of the sky at soft X-ray energies allowed researchers to observe activity that traditional gamma-ray detectors typically miss. Because most X-ray telescopes require a gamma-ray trigger to begin observations, they often arrive too late to capture the earliest stages of such events. The findings, published in Science Bulletin, suggest that this prolonged soft X-ray emission may be more common in compact-object mergers than previously understood.

Potential Magnetar Remnant

The observed X-ray activity, characterized by rapid variability and a changing spectrum, suggests that the central engine created by the merger continued to release energy long after the initial flash. Researchers propose that the remnant could be a magnetar—a rapidly rotating, highly magnetized neutron star—which would account for the sustained emission. This discovery provides a new method for studying gravitational-wave sources.