During the campaign, LHAASO recorded pronounced flares in ultra-high-energy gamma rays, with strong timing links to signals detected in the GeV band. This energy gap—spanning roughly one million times—provides a stringent test of emission models and particle acceleration mechanisms near compact objects. Notably, LHAASO saw no comparable signal during quiescent periods, underscoring that the extreme output is episodic.

The flare intervals included simultaneous detections by both LHAASO and the Fermi satellite. The dual-instrument agreement strengthens the case that the same astrophysical event produces radiation across widely separated energies. Such coordinated behavior is essential for interpreting variability patterns in high-energy astrophysics.

A key outcome is the detection of a 4.8-hour periodicity in the gamma-ray signal. This period matches the orbital modulation of the binary system, indicating that the emission region and/or interaction geometry changes systematically over the orbit. By exploiting this timing signature, researchers achieved exceptionally precise localization.

The accelerator’s position is constrained to a region about three times the Sun’s diameter. For an ultra-high-energy particle source, this represents the highest-precision localization reported, enabling more targeted physical interpretations of where and how acceleration occurs. It also improves the prospects for follow-up observations across wavelengths.

Confirming Cygnus X-3 as the first ultra-high-energy gamma-ray source showing clear temporal variability adds momentum to ultra-high-energy time-domain astronomy. It also offers a new observational route for probing extreme environments near black holes and other compact remnants. Because cosmic rays carry information about their acceleration sites, the results have implications beyond gamma rays.

The findings were produced through collaboration among scientists from the Institute of High Energy Physics (Chinese Academy of Sciences), the Tsung-Dao Lee Institute at Shanghai Jiao Tong University, the Shanghai Astronomical Observatory (Chinese Academy of Sciences), and additional institutions. The work was published in 2026 in National Science Review under the title “Cygnus X-3: A variable petaelectronvolt γ-ray source,” with authors including Zhen Cao, Cong Li, Jieshuang Wang, Jianeng Zhou, and Felix Aharonian.

Since appearing in the scientific discussion, the study has generated major interest worldwide. Within six months of being posted on a preprint server, it reportedly garnered nearly 20 citations—fueling its status as a viral, must-read development in astrophysics and high-energy research.

Keywords

Cygnus X-3; LHAASO; petaelectronvolt gamma rays; cosmic rays; orbital modulation; time-domain astronomy
Subject of Research: Ultra-high-energy gamma-ray emission and cosmic-ray acceleration in the Cygnus X-3 binary system
Article Title: Cygnus X-3: A variable petaelectronvolt γ-ray source
News Publication Date: 2026
Web References: http://dx.doi.org/10.1093/nsr/nwag435
References: 10.1093/nsr/nwag435
Image Credits: Not provided