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LHAASO Detection of Ultra-High-Energy Gamma-Ray Emission toward the Giant Molecular Clouds

The $γ$-ray from Giant molecular clouds (GMCs) is regarded as the most ideal tool to perform in-situ measurement of cosmic ray (CR) density and spectra in our Galaxy. We report the first detection of $γ$-ray emissions in the very-high-energy (VHE) domain from the five nearby GMCs with a stacking analysis based on a 4.5-year $γ$-ray observation with the Large High Altitude Air Shower Observatory (LHAASO) experiment. The spectral energy distributions derived from the GMCs are consistent with the expected $γ$-ray flux produced via CR interacting with the ISM in the energy interval 1 - 100 $~\rm$ TeV. In addition, we investigate the presence of the CR spectral `knee' by introducing a spectral break in the $γ$-ray data. While no significant evidence for the CR knee is found, the current KM2A measurements from GMCs strongly favor a proton CR knee located above 0.9$~\rm$ PeV, which is consistent with the latest measurement of the CR spectrum by ground-based experiments.

preprint2026arXivOpen access

Zhen Cao F. Aharonian Y. X. Bai Y. W. Bao D. Bastieri X. J. Bi Y. J. Bi W. Bian A. V. Bukevich C. M. Cai W. Y. Cao Zhe Cao J. Chang J. F. Chang A. M. Chen E. S. Chen G. H. Chen H. X. Chen Liang Chen Long Chen M. J. Chen M. L. Chen Q. H. Chen S. Chen S. H. Chen S. Z. Chen T. L. Chen X. B. Chen X. J. Chen Y. Chen N. Cheng Y. D. Cheng M. C. Chu M. Y. Cui S. W. Cui X. H. Cui Y. D. Cui B. Z. 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 C. F. Feng H. Feng L. Feng S. H. Feng X. T. Feng Y. Feng Y. L. Feng S. Gabici B. Gao C. D. Gao Q. Gao W. Gao W. K. Gao M. M. Ge T. T. Ge L. S. Geng G. Giacinti G. H. Gong Q. B. Gou M. H. Gu F. L. Guo J. Guo X. L. Guo Y. Q. Guo Y. Y. Guo Y. A. Han O. A. Hannuksela M. Hasan H. H. He H. N. He J. Y. He X. Y. He Y. He S. Hernández-Cadena B. W. Hou C. Hou X. Hou H. B. Hu S. C. Hu C. Huang D. H. Huang J. J. Huang T. Q. Huang W. J. Huang X. T. Huang X. Y. Huang Y. Huang Y. Y. Huang X. L. Ji H. Y. Jia K. Jia H. B. Jiang K. Jiang X. W. Jiang Z. J. Jiang M. Jin S. Kaci M. M. Kang I. Karpikov D. Khangulyan D. Kuleshov K. Kurinov B. B. Li Cheng Li Cong Li D. Li F. Li H. B. Li H. C. Li Jian Li Jie Li K. Li L. Li R. L. Li S. D. Li T. Y. Li W. L. Li X. R. Li Xin Li Y. Li Y. Z. Li Zhe Li Zhuo Li E. W. Liang Y. F. Liang S. J. Lin B. Liu C. Liu D. Liu D. B. Liu H. Liu H. D. Liu J. Liu J. L. Liu J. R. Liu M. Y. Liu R. Y. Liu S. M. Liu W. Liu X. Liu Y. Liu Y. N. Liu Y. Q. Lou Q. Luo Y. Luo H. K. Lv B. Q. Ma L. L. Ma X. H. Ma J. R. Mao Z. Min W. Mitthumsiri G. B. Mou H. J. Mu A. Neronov K. C. Y. Ng M. Y. Ni L. Nie L. J. Ou P. Pattarakijwanich Z. Y. Pei J. C. Qi M. Y. Qi J. J. Qin A. Raza C. Y. Ren D. Ruffolo A. Sáiz D. Semikoz L. Shao O. Shchegolev Y. Z. Shen X. D. Sheng Z. D. Shi F. W. Shu H. C. Song Yu. V. Stenkin V. Stepanov Y. Su D. X. Sun H. Sun Q. N. Sun X. N. Sun Z. B. Sun N. H. Tabasam J. Takata P. H. T. Tam H. B. Tan Q. W. Tang R. Tang Z. B. Tang W. W. Tian C. N. Tong L. H. Wan C. Wang G. W. Wang H. G. Wang J. C. Wang K. Wang Kai Wang L. P. Wang L. Y. Wang R. Wang W. Wang X. G. Wang X. J. Wang X. Y. Wang Y. Wang Y. D. Wang Z. H. Wang Z. X. Wang Zheng Wang D. M. Wei J. J. Wei Y. J. Wei T. Wen S. S. Weng C. Y. Wu H. R. Wu Q. W. Wu S. Wu X. F. Wu Y. S. Wu S. Q. Xi J. Xia J. J. Xia G. M. Xiang D. X. Xiao G. Xiao Y. L. Xin Y. Xing D. R. Xiong Z. Xiong D. L. Xu R. F. Xu R. X. Xu W. L. Xu L. Xue D. H. Yan T. Yan C. W. Yang C. Y. Yang F. F. Yang L. L. Yang M. J. Yang R. Z. Yang W. X. Yang Z. H. Yang Z. G. Yao X. A. Ye L. Q. Yin N. Yin X. H. You Z. Y. You Q. Yuan H. Yue H. D. Zeng T. X. Zeng W. Zeng X. T. Zeng M. Zha B. B. Zhang B. T. Zhang C. Zhang F. Zhang H. Zhang H. M. Zhang H. Y. Zhang J. L. Zhang Li Zhang P. F. Zhang P. P. Zhang R. Zhang S. R. Zhang S. S. Zhang W. Y. Zhang X. Zhang X. P. Zhang Yi Zhang Yong Zhang Z. P. Zhang J. Zhao L. Zhao L. Z. Zhao S. P. Zhao X. H. Zhao Z. H. Zhao F. Zheng W. J. Zhong B. Zhou H. Zhou J. N. Zhou M. Zhou P. Zhou R. Zhou X. X. Zhou B. Y. Zhu C. G. Zhu F. R. Zhu H. Zhu K. J. Zhu Y. C. Zou X. Zuo Y. H. Yu

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LHAASO Detection of Ultra-High-Energy Gamma-Ray Emission toward the Giant Molecular Clouds

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