Speaker
Description
We report a dedicated study of the newly discovered extended ultra-high-energy (UHE) γ-ray source 1LHAASO J1839-0545u using data collected between December 2019 and July 2025. The source is significantly detected with statistical significances of 24σ, 25σ, and 16σ in the 1–25 TeV, 25–100 TeV, and >100 TeV energy bands, respectively. Its morphology is best described by a disk model with an extension of 0.41deg±0.02deg.
The position and spatial extension are highly consistent with those of FGES J1839.4−0554 detected above 10 GeV of Fermi-LAT, suggesting a common origin. Recent observations by Einstein Probe also reveal extended hard X-ray emission in the same region, characterized by an unusually hard photon index of ~1.2. In addition, analysis of MWISP 12CO data indicates the presence of associated dense molecular clouds.
A candidate supernova remnant, G26.6−0.1, lies within the region, providing a plausible site for particle acceleration. We propose that the broadband emission from X-rays to GeV–TeV γ-rays can be interpreted within a unified scenario in which high-energy particles accelerated by the SNR interact with the surrounding molecular environment.
In this framework, the γ-ray emission is naturally explained by hadronic interactions with dense gas, while the unusually hard X-ray spectrum can be attributed to nonthermal bremsstrahlung from an electron population whose low-energy spectrum is flattened by Coulomb losses in dense environments.
This scenario provides a self-consistent interpretation of the multi-wavelength morphology and spectral properties, and suggests that the source may represent an efficient cosmic-ray accelerator embedded in a dense environment.
