Since its launch in January 2024, the Einstein Probe (EP) has fundamentally transformed our view of the dynamic X-ray universe. This pioneering mission, led by the Chinese Academy of Sciences (CAS), is now delivering a steady stream of discoveries, uncovering rare and explosive cosmic events that were once too faint for other telescopes to catch.

The Einstein Probe is equipped with two complementary X-ray telescopes. Its Wide-field X-ray Telescope (WXT) utilizes novel lobster-eye optics to monitor one-tenth of the entire sky in a single shot, providing unprecedented sensitivity to faint, transient events. For detailed follow-up, the Follow-up X-ray Telescope (FXT) offers a larger effective area and superior angular resolution to pinpoint and study discoveries.

On November 24, 2025, at a press conference showcasing new findings from the Space Science Strategic Priority Program, the Einstein Probe unveiled three significant scientific discoveries.

A Cosmic Explosion in Slow-evolving

Einstein Probe discovered a new X-ray transient, EP241021a, that defies the brief, violent nature of typical cosmic outbursts. This event persisted for at least 40 days, like a slow-down cosmic firework, and was accompanied by a relativistic jet.

Such a prolonged and luminous eruption is extremely rare. Astronomers speculate it could be the signature of a star being torn apart by a rare intermediate-mass black hole or a new type of jetted explosion.

"This discovery offers new insights into the catastrophic explosion and the launching of a relativistic jet," said Professor Shu Xinwen of Anhui Normal University, the lead author of the study. "It also provides potentially valuable clues for studying the enigmatic class of intermediate-mass black holes."

Figure 1: Illustration of EP241021a (Credit: Sci Visual/EPSC)

A Faint 'Lurker' in the Milky Way

In September 2024, the probe captured an exceptionally faint X-ray burst, dubbed EP240904a, from within our own galaxy. Its observational characteristics—including its X-ray "heartbeat" and spectral evolution—identified it as a new black hole candidate. The outburst was about 100 times dimmer than typical black hole eruptions, explaining why it had remained hidden in previous observations.

"The discovery of EP240904a opens a new window for unveiling the hidden population of black holes in the Milky Way," said Dr. Cheng Huaqing, the first author from the National Astronomical Observatories of China (NAOC).

"The faintness of this source is not a weakness but a revelation," added Professor Tao Lian from the Institute of High Energy Physics, the corresponding author. "EP240904a is clear evidence of this 'hidden' population. With the Einstein Probe, we now have the key capability to uncover these 'silent' black holes systematically."

Figure 2: Illustration of EP240904a (Credit: Sci Visual/EPSC)

An exceptionally soft X-ray flash, probing the diversity of gamma-ray bursts and stellar core-collapse events.

The mission's autonomous capabilities were spotlighted with the discovery of EP240801a. The probe detected the transient and immediately triggered its FXT instrument for follow-up observations. A joint analysis with NASA's Fermi satellite revealed the event to be an extremely "soft" X-ray flash, a rare type of explosion in which low-energy X-rays dominate radiation. Its extreme properties provide new clues to the diversity of gamma-ray bursts and stellar core-collapse events.

"This event showcases Einstein Probe's core capabilities, as it completed the full process from discovery to tracking autonomously," said Dr. Xu Dong from NAOC, the corresponding author. "This performance marks it as a brilliant and efficient cosmic monitoring platform."

Figure 3: Comparison of EP240801a to Fermi GRBs. The histogram shows the distribution of the fluence ratio S(25 − 50 keV)/S(50 − 100 keV) for 1647 Fermi GRBs. The red line represents the fluence ratio of EP240801a, and the shadow is the 1σ uncertainty interval. The blue dashed lines represent the boundaries of Classical GRBs (C-GRBs), X-Ray-Rich GRBs (XRRs), and X-Ray Flashes (XRFs) described by Sakamoto et al. (2008).

Establishing a Key Role in Time-Domain Astronomy

"Although these three results focus on different types of celestial objects, they collectively highlight the powerful capability of Einstein Probe in the field of time-domain astronomy," said Professor Yuan Weimin, the mission's Principal Investigator. "The probe can capture fleeting flashes, monitor week-long processes, and detect faint signals hidden in the dark. These findings establish Einstein Probe as a key player at the forefront of international research in high-energy astrophysical observations."

The Einstein Probe (EP) is a pioneering mission dedicated to time-domain astronomy, specifically designed to monitor the sky in the soft X-ray band. The mission is spearheaded by the Chinese Academy of Sciences (CAS) with international collaboration from the European Space Agency (ESA), Max Planck Institute for Extraterrestrial Physics (MPE) in Germany, and the French National Centre for Space Studies (CNES). EP is set to operate for a nominal 3 years and can be extended to 5 years.

References

Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics

Shu et al. 2025, The Astrophysical Journal Letters, Volume 990, Issue 1, id.L29, 21 pp.

H. Q. Cheng; Q. C. Zhao; L. Tao et al. The Astrophysical Journal Letters, 991, L41 (2025)

Jiang, Shuai-Qing; Xu, Dong; et al. The Astrophysical Journal Letters, Volume 988, Issue 1, id.L34, 18 pp.

Please find the links below for the publication details:

https://iopscience.iop.org/article/10.3847/2041-8213/adf4cd

https://iopscience.iop.org/article/10.3847/2041-8213/adf104

https://iopscience.iop.org/article/10.3847/2041-8213/addebf