Discovery to unravel mystery of early universe

Scientists have revealed new insights into the distant X-ray universe, with the Einstein Probe satellite offering fresh perspectives on the distant explosions in the cosmos.

The research results of its discovery of a mysterious blast of X-rays in March — less than three months after EP was launched in January last year — was published on international academic journal Nature Astronomy on Thursday.

The discovery could require us to change the way we explain the extraordinary explosions known as gamma-ray bursts, said Liu Yuan, co-first author of the paper and a scientist from National Astronomical Observatories, Chinese Academy of Sciences.

The burst of low-energy X-rays EP's Wide-field X-ray Telescope detected in March lasted for more than 17 minutes, and fluctuated in brightness before fading away again. Such an event is known as a fast X-ray transient, or FXRT, and this particular transient was designated as EP240315a.

"EP240315a was the first time astronomers had detected soft X-rays for such a long duration from such an ancient explosion," Liu said. "It was really good to see the WXT onboard trigger algorithm working fine for this event."

About one hour after the X-rays were seen, a telescope situated in South Africa as part of the Asteroid Terrestrial-Impact Last Alert System detected visible light from the same location.

Follow-up observations from the Gemini-North telescope on Hawaii Island and the Very Large Telescope in Chile returned redshift measurements that confirmed that the burst had come from around 12.5 billion light-years away, beginning its cosmic journey to us when the universe was just 10 percent its current age.

"The detection of EP240315a demonstrates Einstein Probe's great potential for discovering transients from the early universe. The mission will play an important role in international observations and collaborations," said Wu Xuefeng, one of the paper's authors and a researcher at the Purple Mountain Observatory of the CAS in Nanjing, Jiangsu province.

In later analyses, the X-rays were found to be coincident with a gamma-ray burst.

These results show that a substantial fraction of FXRTs may be associated with gamma-ray burst, and that sensitive X-ray monitors such as EP can pinpoint them in the distant universe, said Roberto Ricci, a research fellow from University of Rome Tor Vergata in Italy.

Combining the power of X-ray and radio observations hands researchers a new way to explore these ancient explosions even without detecting their gamma rays, he said.

yandongjie@chinadaily.com.cn