Einstein Probe Detects Mysterious Blast of X-Rays from the Early Universe

On March 15, 2024, a space-based observatory detected bursts of low-energy X-rays from deep within the ancient universe, fluctuating in brightness for more than 17 minutes before fading. About an hour later, ground-based telescopes picked up visible light from the same source, tracing it back to when the universe was only a billion years old.

U newly launched Einstein Probe is already spotting distant explosions with the potential to shake up what we know about the early years of the universe. Using its wide-field X-ray telescope, the spacecraft detected so-called, or low-energy, X-rays that lasted for an unusually long period of time. These events are known as fast X-ray transients (FXRTs), and the newly spotted burst has been designated EP240315a.

After monitoring the burst at radio wavelengths for a period of three months, the team of astronomers behind the detection confirmed that the energy output was consistent with a gamma-ray burst dated when the universe was only 10 percent of its current age. Therefore, given the estimated age of the universe at 13.8 billion years, the explosion occurred when the universe was about 1.38 billion years old.

“These results show that a substantial fraction of FXRT can be associated with (gamma-ray bursts) and that sensitive X-ray monitors, such as Einstein Probe, can identify them in the distant Universe,” Roberto Ricci, researcher at the Università di Rome Tor Vergata, Italy, and one of the authors behind the new paper detailing the discovery, said in a declaration. “Combining the power of X-ray and radio observations gives us a new way to explore these ancient explosions even without detecting their gamma rays.”

EP240315a marks the first time X-rays have been detected from an ancient explosion that lasted for such a long time. Follow-up 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 explosion had come from about 12.5 billion light years away.

Gamma-ray bursts are short bursts of high-energy light and the most powerful explosions in the universe, typically triggered by the collapse of massive stars or the fusion of neutron stars. Those bursts are also known to emit copious amounts of X-rays. The newly discovered soft X-rays were traced to GRB 240315C, a gamma-ray burst first detected by the Burst Alert Telescope (BAT) at the Swift Observatory in NASA’s Neil Gehrels, with additional data provided by the Konus instrument aboard NASA’s Wind spacecraft.

Although gamma rays are associated with X-rays, the recently discovered fast X-ray transient is an anomaly. X-rays typically precede 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 team member at the Einstein Probe Science Center at the National Astronomical Observatories, Chinese Academy of Sciences, and co-author of the new study, said. said in a statement.

The mystery behind the long time between X-rays and gamma-ray bursts, in addition to the long duration of the X-rays themselves, are reasons to wonder if gamma-ray bursts explode the way the scientists believe them.

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 January 9, 2024. Its Wide-field X-ray telescope takes in X-ray light in square tubes in a grid, which means it can observe 3,600 square degrees (under less than a tenth of the celestial sphere) in a single stroke.

“As soon as we opened Einstein Probe’s eyes to the sky, it found new interesting phenomena,” said Erik Kuulkers, ESA’s Einstein Probe project scientist, in a statement. “That’s pretty good and should mean there are many more interesting discoveries to come.”