Science1 publisher2 min readPublished
Einstein Probe tracked soft X-rays for nearly 10 minutes after a 0.4-second gamma-ray burst
Einstein Probe saw a likely neutron star merger shine in soft X-rays for nearly 10 minutes after a 0.4-second gamma-ray burst. Its team argues gamma-ray detectors alone may have missed this phase in earlier mergers, a case that so far rests on one event.
The Scientist · Science desk
Drafted by a language model from the sources cited here and checked against its claim ledger before publication. How we use AISend a correction
What happened
- The event is catalogued as EP250704a in X-rays and GRB 250704B in gamma rays, and was recorded jointly by Einstein Probe, SVOM and the Insight-HXMT telescope.
- Einstein Probe's wide-field telescope had the source in view from its onset and logged several separate episodes of soft X-ray emission after the gamma rays faded.
- Most X-ray telescopes turn to a burst only after a gamma-ray detector has located it, so the earliest X-ray light can be over before they begin observing.
- According to the team, rapid variability and a changing spectrum in the X-rays indicate that the engine formed in the merger kept releasing energy.
- The findings were published as a cover article in the journal Science Bulletin.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- decision Planners of merger follow-up now have a measured case for continuous wide-field X-ray monitoring, since any telescope that slews after a gamma-ray trigger starts late by design.
- constraint Burst durations and energy totals compiled from gamma-ray triggers may cover only the opening of each event, so population studies built on them need X-ray coverage before treating them as complete.
- capability If later events show the same minutes-long tail, gravitational-wave searches would gain a longer electromagnetic window in which to locate and study a merger.
Ten minutes is 600 seconds. Against a burst of about 0.4 seconds, the X-ray activity lasted roughly 1,500 times longer than the flash that would normally define the event [4][1]. Einstein Probe saw it because the mission watches a wide area of sky continuously at soft X-ray energies [7]. According to the release, conventional gamma-ray observations would likely have missed the phase [1].
What powered those minutes is less settled. The team says one possible explanation is a magnetar, a rapidly rotating, highly magnetized neutron star that kept powering the X-ray emission [9]. Bing Zhang is a co-author and the founding director of the Hong Kong Institute for Astronomy and Astrophysics. He has long proposed that binary neutron star mergers could produce fast X-ray transients that missions such as Einstein Probe could detect [13]. In my view, a prediction confirmed inside its proponent's own collaboration makes an independent analysis of the next such event more valuable than usual.
The team, led by An Li of Beijing Normal University and Bin-Bin Zhang of Nanjing University, argues that similar soft emission may have been present in earlier short bursts. On their account it went unseen because it was too soft and faint for gamma-ray instruments [10]. The selection-effect argument is reasonable but so far rests on one detection. The release does not say how many earlier bursts were re-examined, or whether a gravitational-wave signal was recorded. Short gamma-ray bursts are commonly associated with colliding compact objects such as neutron stars [14], and phys.org calls this one a likely neutron star merger [15].
Yi-Han Iris Yin, a PhD student at the University of Hong Kong, led the analysis of the high-energy prompt emission and is a co-corresponding author [16]. "Einstein Probe is allowing us to uncover a part of compact star mergers that was hidden from previous gamma-ray observations," Yin said [12]. "The short gamma-ray flash may represent only the beginning of the high-energy activity." [12]
What to watch
- An archival search of earlier short gamma-ray bursts for faint soft X-ray tails, to test whether EP250704a is typical.
- A short burst that coincides with both a gravitational-wave detection and an Einstein Probe X-ray tail, pinning the source as a neutron star merger.
- Further Einstein Probe detections of minutes-long X-ray activity, and whether their light curves fit a magnetar-powered engine.