First Detection of Ultrahigh Energy Emission from Gamma-Ray Binary LS I + 61 ° 303

Physical Review Letters 2026 Open access

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Authors: Z D Cao, F. Aharonian, Y. X. Bai, Yiwang Bao, D. Bastieri, Xiao-Jun Bi, Y.J Bi, W Bian, A. V. Bukevich, C. M. Cai, W. Y. Cao, Z D Cao
+88 more J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, G. H. Chen, H. X. Chen, Liang Chen, Long Chen, Liang Chen, Long Chen, Q. H. Chen, S. Z. Chen, Shengyong Chen, S K Chen, Shengyong Chen, X. B. Chen, Y.D Cheng, Y. Chen, N. Cheng, Y. D. Cheng, M. C. Chu, Maxwell Cui, S. W. Cui, X. H. Cui, Y M Cui, Bowei Dai, H. L. Dai, Z. G. Dai, Danzengluobu, Y. X. Diao, X Q Dong, K. K. Duan, J. H. Fan, Y. Z. Fan, J. Fang, J. H. Fang, K. Fang, Y. L. Feng, H. Feng, L. Feng, Kai Fang, X H Feng, H Feng, Li Feng, S. Gabici, B. Gao, C. D. Gao, Q. Gao, Wei Gao, Bin Gao, M. M. Ge, T. T. Ge, L. S. Geng, Gwenael Giacinti, G. Gong, Q. B. Gou, M. H. Gu, F.L. 福来 Guo 郭, Jing Guo, Xu Guo, Yi Guo, Jing Guo, Y.A Han, O. A. Hannuksela, M. Hasan, H. He, H. He, H. B. Hu, Xing‐Xiang He, Y. He, S. Hernández-Cadena, Bowen Hou, C. Hou, X. Hou, H. B. Hu, S. C. Hu, Chun-Hao P. Huang, D.H Huang, Jian‐Jang Huang, Ting Huang, Chun-Hao P. Huang, XJ Huang, X. Y. Huang, Y. Huang, Yu Huang, X. L. Ji, H. Y. Jia, K. Jia
DOI: 10.1103/7xhp-tff7
Cited by: 2
References: 51

Abstract

We report the first detection of gamma-ray emission up to ultrahigh-energy (UHE; >100 TeV) emission from the prototypical gamma-ray binary system LS I +61° 303 using data from the Large High Altitude Air Shower Observatory. It is detected with significances of 9.2σ in the Water Cherenkov Detector Array (WCDA, 1.4-30.5 TeV) and 6.2σ in the Kilometer Square Array (KM2A, 25-267 TeV); in KM2A alone we identify 16 photonlike events above 100 TeV against an estimated 5.1 background events, corresponding to a 3.8σ detection. These results provide compelling evidence of extreme particle acceleration in LS I +61° 303. Furthermore, we observe orbital modulation at 3.9σ confidence level, between 25 and 100 TeV, with a hint that the orbital modulation is energy dependent. These features can be understood in a composite scenario in which leptonic and hadronic processes jointly contribute.

Fields of Study & Subjects

Astrophysics and Cosmic Phenomena Astrophysical Phenomena and Observations Gamma-ray bursts and supernovae

Publication details

Journal / source
Physical Review Letters
Publisher
American Physical Society (APS)
Volume
136
Issue
18
Pages
181001–181001
Publication date
9 March 2026
Language
EN