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The Einstein Probe telescope captured for the first time a long X-ray 'echo' after an instant gamma-ray burst — like thunder after lightning.
Abstract
The short gamma-ray burst GRB 250704B, lasting only 0.4 seconds, came with an unexpectedly long soft X-ray afterglow: the Einstein Probe telescope caught it for roughly 560 seconds. This is a direct detection of an extended X-ray component in an event that otherwise looked like a typical short GRB. Until now, astronomers only suspected these 'tails' existed but never saw them directly. The discovery suggests that prolonged X-ray emission is a common feature of neutron star mergers and will become a promising electromagnetic marker for catching gravitational waves.
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The Einstein Probe space telescope detected a celestial storm: after a short (0.4-second) gamma-ray burst — a cosmic lightning bolt — came a long roll of X-ray thunder. It lasted nearly 10 minutes. This is the first direct proof that such explosions leave a lingering X-ray afterglow.
These events are caused by collisions of neutron stars or black holes. The impact produces an instantaneous gamma-ray flash, and then the crash site continues to emit soft X-rays for a long time. This tail not only tells us about the merger details — it helps locate the source, even after the gravitational waves, the tremors of space, have subsided.
But the biggest surprise is the power. In those same 10 minutes, this X-ray echo releases as much energy as hundreds of billions of Suns shining at once.
🎯 In 10 minutes, this X-ray signal releases energy equivalent to the luminosity of hundreds of billions of Suns.
