On March 15, 2024, a space-based observatory detected bursts of low-energy X-rays from deep in the ancient universe, fluctuating in brightness for more than 17 minutes before going away. About an hour later, ground-based telescopes picked up visible light from the same source, tracing it back to when the universe was only about billions of years old.
The Recently launched Einstein probe are already spotting distant explosions with the potential to take away what we know about the earliest years of the universe. Using its wide-field X-ray telescope, the spacecraft detected so-called soft, or low-energy, X-rays that lasted an unusually long time. These events are known as Fast X-Ray Transients (FXRT), and the newly spotted burst has been designated EP240315A.
After monitoring the burst at radio wavelengths over a period of three months, the team of astronomers behind the detection confirmed that the energy output was consistent with a gamma-ray burst dating back to when the universe was only 10 percent of its current age. So given the estimated age of 13.8 billion years of the universe, the explosion occurred when the universe was about 1.38 billion years old.
“These results show that a large fraction of FXRTs can be associated with [gamma-ray bursts] and that sensitive X-ray monitors, as Einstein Probe can count them in the distant universe, “Roberto Ricci, researcher at the University of Rome Tor Vergata, Italy, and one of the authors behind the new paper detailing the discovery, said in Statement. “Combining the power of X-ray and radio observations gives us a new way to investigate these ancient explosions without even detecting their gamma rays.”
EP240315A marks the first time soft X-rays have been detected from an ancient explosion that lasted this long. Subsequent observations using the Gemini North Telescope in Hawaii and the Very Large Telescope in Chile measured visible light from the same location, which confirmed that the burst came from about 12.5 billion light years away.
Gamma-ray bursts are brief flashes of high-energy light and the most powerful explosions in the universe, typically triggered by the collapse of massive stars or the merger of neutron stars. These explosions are also known to emit copious amounts of X-rays. The newly discovered soft X-rays were traced back to GRB 240315C, a gamma-ray burst first detected by the Burst Alert Telescope (BAT) on NASA’s Neil Gehrels Swift observatory, with additional data provided by the Konus instrument on the wind from NASA.
Although gamma-ray bursts are associated with X-rays, the recently discovered fast X-ray transit is an anomaly. The X-rays typically precede the gamma-rays by a few tens of seconds, but EP240315A was seen more than six minutes (372 seconds) before GRB 240315C. “Such a long delay has never been observed before,” Hui Sun, a member of the Einstein Probe Science Center at the National Astronomical Observatories, Chinese Academy of Sciences, and co-author of the new study, said in a statement.
The mystery behind the long duration of time between the X-rays and the gamma-ray burst, in addition to the long duration of the X-rays themselves, are reasons to question whether gamma-ray bursts explode as scientists believe them to.
The Einstein probe, an X-ray telescope managed by the Chinese Academy of Sciences, and built in collaboration with the European Space Agency and the Max Planck Institute for Extraterrestrial Physics, launched on the 9th In X-ray light in square tubes in a grid, which means, that it can observe 3,600 square degrees (just under one tenth of the celestial sphere) in a single shot.
“As soon as we opened the Einstein probe’s eyes to the sky, it found interesting new phenomena,” Erik Kuulkers, ESA’s Einstein Probe Project scientist, said in a statement. “That’s pretty good and must mean there are many more interesting discoveries to come.”