Brief
Einstein Probe detects ten‑minute soft X‑ray afterglow from short GRB 250704B
The wide‑field soft X‑ray monitor captured an extended emission that previous missions missed, linking it to a compact‑object merger.
By Felo News Desk · Published
On 4 July 2025, the Einstein Probe (EP) recorded a short gamma‑ray burst, designated EP250704a/GRB 250704B, that began with a sub‑second flash and was followed by almost ten minutes of soft X‑ray emission, according to a ScienceDaily release.
What happened
The initial flash, lasting less than 0.5 seconds, was detected simultaneously in gamma rays by SVOM‑GRM and Insight‑HXMT and in X‑rays by EP‑WXT. After the onboard alert, EP‑WXT continued to monitor the source, revealing a prolonged soft X‑ray episode that persisted for roughly ten minutes. The extended emission was energetic but so soft that it would have fallen below the detection thresholds of conventional gamma‑ray instruments such as Swift’s Burst Alert Telescope.
What the reports add
Professor Bin‑Bin Zhang of Nanjing University, a co‑corresponding author, explained that earlier missions would have recorded only the brief gamma flash, missing the later X‑ray activity. Professor Eleonora Troja of the University of Rome Tor Vergata highlighted that a coordinated multi‑wavelength follow‑up—spanning X‑ray, optical and radio—identified the burst’s host galaxy, measured its redshift, ruled out an accompanying supernova, and linked the X‑ray emission to a compact‑object merger.
What was said
"The event initially appeared to be an ordinary short GRB, producing a bright flash lasting less than half a second," said An Li, a PhD student at Beijing Normal University and EP’s Transient Advocate. "However, instead of fading away, the source continued emitting episodes of soft X‑rays for nearly ten minutes," Li added. Professor Zhang noted, "Our observations show that what appears to be a typical short gamma‑ray burst can actually conceal a much longer and richer episode of activity at soft X‑ray energies." Professor Troja said, "The coordinated observations across multi‑wavelengths were essential… to identify and study the burst's host galaxy and provide strong evidence linking this extraordinary X‑ray emission to a compact object merger."
How it came about
The detection was made possible by EP’s wide‑field soft X‑ray monitoring, which operates independently of gamma‑ray alerts. The rapid alert allowed Li to begin analysis immediately, and the subsequent international campaign gathered data that confirmed the merger origin, building on earlier Einstein Probe discoveries of long‑lasting X‑ray flashes from neutron‑star mergers.
Key facts
- Einstein Probe recorded a half‑second gamma flash followed by ~10 minutes of soft X‑ray emission from GRB 250704B on 4 July 2025. (sciencedaily.com)
- The extended X‑ray emission was too soft for detection by Swift’s BAT and similar gamma‑ray instruments. (sciencedaily.com)
- Multi‑wavelength follow‑up identified the host galaxy, measured redshift, ruled out a supernova, and linked the emission to a compact‑object merger. (sciencedaily.com)
Sources
- [1] sciencedaily.com — originally reported as “Einstein Probe reveals a hidden phase of neutron star collisions”
