Einstein Probe Revealed a 9-Minute X-Ray Phase After GRB 250704B

A brief gamma-ray flash can make an event look over almost as soon as it begins. On July 4, 2025, Einstein Probe detected a different story from EP250704a, also known as GRB 250704B: after a gamma-ray burst lasting about 0.4 seconds, the source produced soft X-rays for roughly 560 seconds. That extended signal suggests a distinct phase of activity that could be missed without soft X-ray observations. 12

The finding adds a new way to look for activity following compact-object mergers. It also raises a question about what powered the emission: one interpretation fits a long-lived, rapidly spinning magnetar, but the observations do not confirm the remnant’s identity. 211

A short burst, followed by minutes of soft X-rays

GRB 250704B was classified as a short gamma-ray burst, with a total duration of about 0.4 seconds. Einstein Probe’s Wide-field X-ray Telescope detected a much longer signal in the soft X-ray band, at 0.5–4 keV: about 560 seconds of emission following the burst. 12

The distinction matters. The reported variability and spectrum do not fit a simple picture in which a hard gamma-ray spike is followed only by a standard external-shock afterglow. The study instead describes the soft X-rays as a separate, prolonged phase of prompt emission—one that observations focused on harder energies could miss. 2

Follow-up observations reveal a more complex event

Observations beyond the initial flash help show why the event drew interest. A multiwavelength analysis reported prolonged X-ray emission and an unusual optical and infrared plateau lasting about a day, followed by a rapid decline. Its analysis covered radio through gamma-ray wavelengths and tracked the event over nearly two days.

That broader dataset supports a model in which a millisecond magnetar—an extremely magnetized, rapidly rotating neutron star—continues to power activity after the burst. In that interpretation, the X-rays are linked to energy released as the magnetar spins down, while the optical and infrared emission is explained as afterglow radiation receiving continued energy input. These are model-based explanations of the observations, not direct confirmation of a magnetar. 11

What the event could mean for neutron-star mergers

If the magnetar interpretation is correct, the remnant remained active long enough to power emission after the short gamma-ray burst. That makes the event relevant to questions about what happens when compact objects merge and whether a neutron-star remnant can survive rather than collapse promptly. The soft X-ray signal also offers a potential electromagnetic clue to seek alongside gravitational-wave observations in future merger events. 211

The neutron-star equation of state describes how ultra-dense matter behaves, including how much mass a neutron star can support. In principle, reliable measurements of a merger’s mass and its remnant’s fate could help test competing descriptions of that matter. But EP250704a does not, on its own, establish the remnant’s nature or provide a direct measurement of the equation of state. Its value is that it reveals a potentially useful signal to investigate in future events. 211

The takeaway

Einstein Probe showed that a burst lasting less than half a second can be followed by nearly ten minutes of soft X-ray activity. Together with the optical, infrared and radio follow-up, that signal supports a more extended and complicated picture of the event than the gamma-ray flash alone would suggest. A magnetar-powered remnant is a plausible explanation—and a promising lead for studying merger aftermaths—but remains an interpretation rather than a settled result. 1211