Einstein Probe Detects Early Universe Explosion, Opening New Window for Studying Young Cosmos

China's Einstein Probe Detects Soft X-ray Signals from Early Universe Explosion

China's Einstein Probe (EP) astronomical satellite has made a groundbreaking discovery, detecting soft X-ray signals from an explosion in the early universe for the first time. This opens a new window for studying the young cosmos.

The findings were published in the journal Nature Astronomy. The Wide-field X-ray Telescope onboard the EP satellite observed a faint pulse signal from a burst event in the soft X-ray band on March 15, 2024. This burst, designated as EP240315a, exhibited rapid brightness fluctuations and persisted for over 17 minutes before fading away.

Subsequent observations by telescopes from other countries confirmed that this burst originated from the distant early universe. At the time of this burst, the universe was only 10 percent of its current age, and its signal took 12.5 billion years to reach Earth.

soft X-rays have lower energy, while hard X-rays have higher energy.

Yuan Weimin, principal investigator of the EP mission and a researcher at the National Astronomical Observatories of the Chinese Academy of Sciences (CAS), said this is just the beginning and the discovery showcases the remarkable potential of EP in detecting cosmic explosions from the early universe.

The discovery of EP240315a also facilitated a collaboration between the EP team and Dr. Roberto Ricci from the University of Rome Tor Vergata in Italy. He initiated long-term radio band monitoring of this gamma-ray burst (GRB). Using the Australia Telescope Compact Array, his three-month radio observations confirmed that EP240315a's energy output aligns with the characteristics of a GRB.

GRBs are among the most powerful explosive phenomena known in the universe, typically originating from the explosion of massive stars. Subsequent analysis revealed that EP240315a is associated with a GRB designated as GRB240315C.

"These results show that a substantial fraction of FXRTs (fast X-ray transients) may be associated with GRBs and that sensitive X-ray monitors, such as the EP, can pinpoint them in the distant universe, and combining the power of X-ray and radio observations hands us a new way to explore these ancient explosions even without detecting their gamma rays," said Dr. Roberto Ricci.

However, the mystery remains, as the GRB discovered by EP is particularly unique. Under normal circumstances, X-rays appear tens of seconds earlier than gamma rays, but in the case of EP240315a, the X-rays arrived more than six minutes earlier.

"Such a long delay has never been observed before," said Sun Hui, an associate researcher at the National Astronomical Observatories of CAS and one of the study's co-first authors.

Gao He, a co-corresponding author from Beijing Normal University, noted that this discovery offers a fresh perspective and could lead to a re-evaluation of existing GRB models.