Measurement of Very-High-Energy Diffuse Gamma-Ray Emissions from the Galactic Plane with LHAASO-WCDA

The diffuse Galactic gamma-ray emission is a very important tool used to study the propagation and interaction of cosmic rays in the Milky Way. In this Letter, we report the measurements of the diffuse emission from the Galactic plane-covering Galactic longitudes from 15° to 235° and latitudes from -5° to +5°, in an energy range of 1 to 25 TeV-made with the Water Cherenkov Detector Array (WCDA) of the Large High Altitude Air Shower Observatory. After the sky regions of known sources are masked, the diffuse emission is detected with 24.6σ and 9.1σ significance in the inner Galactic plane (15°<l<125°, |b|<5°) and outer Galactic plane (125°<l<235°, |b|<5°), respectively. The WCDA spectra in both regions can be well described by a power-law function, with spectral indices of -2.67±0.05_{stat} in the inner region and -2.83±0.19_{stat} in the outer region, respectively. Combined with the Square Kilometer Array (KM2A) measurements at higher energies, a clear softening of the spectrum is found in the inner region, with change of spectral indices by ∼0.5 at a break energy around 30 TeV. The fluxes of the diffuse emission are higher by a factor of 1.5-2.7 than the model prediction assuming local cosmic ray spectra and the gas column density, which are consistent with those measured by the KM2A. Along the Galactic longitude, the spatial distribution of the diffuse emission shows deviation from that of the gas column density. The spectral shape of the diffuse emission may vary in different longitude regions. The WCDA measurements bridge the gap between the low-energy measurements by space detectors and the ultra-high-energy observations by KM2A and other experiments. These results suggest that improved modeling of the wideband diffuse emission is required.

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Journal
Physical Review Letters
Published
2025-02-28
DOI
https://doi.org/10.1103/physrevlett.134.081002
Citations
16
Primary Topic
Astrophysics and Cosmic Phenomena
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article
Field-Weighted Citation Impact
29.92

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article

Measurement of Very-High-Energy Diffuse Gamma-Ray Emissions from the Galactic Plane with LHAASO-WCDA

Cong Feng, O. Shchegolev, Y. Chen, Z. X. Wang et al.
16 citations
Physical Review Letters
Astrophysics and Cosmic Phenomena
29.92
article

Measurement of Very-High-Energy Diffuse Gamma-Ray Emissions from the Galactic Plane with LHAASO-WCDA

Cong Feng, O. Shchegolev, Y. Chen, Z. X. Wang, J. H. Fan, T.T Ge, W.L Li, B. Q., E. S. Chen, Bowen Zhao, Zhihao Sun, Hongwei Zhang, Z. G. Yao, H. K. Lv, M. Zha, Hui-Jun Mu, J. Y. Guo, P. P. Zhang, Yuze Li, Ke Jia, W. Zeng, Y. D. Cheng, Kenny C. Y. Ng, K. Li, H. D. Liu, Dezhi Huang, X. R. Li, P. F. Zhang, Wei Gao, Y. Y. Huang, Ali Raza, B. B. Zhang, Y. J. Wang, R. Zhang, J. R. Mao, Y. W. Bao, M. M. Ge, Axikegu, H. C. Song, M. M. Kang, H. H. Wang, D. Kuleshov, Chaoran Yang, H. Liu, Li‐Sheng Geng, M. Zha, G. M. Xiang, Rujun Tang, Bing-Qiang Qiao, Yun‐Lin Liu, S. B. Zhang, Yuan Qian, D. Khangulyan, Weiwei Cao, F Aharonian, M. Qi, Z. B. Tang, C. M. Li, Hong-Cai “Joe” Zhou, Maxwell Cui, J. L. Liu, D. Semikoz, D. X. Xiao, Guomin Wang, M. J. Chen, M. L. Chen, J. L. Zhang, J. C. Wang, Hengying Zhang, Cong Li, Z. Cao, X. G. Wang, X. H. Cui, Q. B. Gou, Lijing Shao, Weixin Bian, Y. L. Xin, Manfei Liu, Qin Cao, Shangrong Lin, Chuyuan Yang, S. Z. Chen, X. Zhang, Z. G. Dai, S. Wu, D. Bastieri, Yichen Fan, J. Takata, D. Liu, W. Liu, Z. H. Wang, Fulai Guo, Q. N. Sun, Q. Luo, Yun-Feng Liang, D. Ruffolo, P. H. T. Tam, Fan Yang, Longjun Wang, Xuzhong Zuo, Wei Wang, X. Y. Huang, S. R. Zhang, Z. Wang, F. Shi, H.Y Jia, Fa‐Kun Zheng, A. M. Chen, Jun‐Qing Xia, Dingrong Xiong, Chun-Hao P. Huang, C. Hou, Y. D. Wang, M. C. Chu, H. B. Jiang, D. B. Liu, Fengchun Shu, Lili Yang, Fang Yang, Lijun Ou, J.C Qi, Y. A. Han, Jun-Jie Wei, G. Xiao, L. H. Wan, Qing-Wen Tang, W. Xu, J. F. Chang, Xu Zhang, J. J. Qin, Jiawei He, W. X. Yang, T. L. Chen, Gwenael Giacinti, H. G. Wang, W. J. Huang, Yang Su, H. M. Zhang, P. H. Wang, R. F. Xu, M. H. Gu, S. M. Liu, M. Zahid Hasan, Y. Q. Guo, J. N. Zhou, X. N. Sun, Yuan-Chuan Zou, Shaoquan Li, Xiong Zhang, X. D. Sheng, Y. F. Zhang, Xiao-Jun Bi, P. Zhou, Bin Zhou, Xianglin Hou, H. B. Hu, K. Kurinov, Jing‐Zhi Yan, H. X. Chen, O. A. Hannuksela, Xin Li, X. Y. Wang, S. Chen, J. F. Chang, A. Sáiz, B. B. Li, Kwok Lung Fan, L. L., Hui Yue, Xue-Feng Wu, Yuhua Yao, Meng Zhou, C. Wang, Huicai Li, V. Stepanov, Liang Chen, A.V Bukevich, Xinhua Ma, Long Chen, Zhe Li, Lu Zhang, Fan Zhang, Zhen Wang, Jie Li, Zhuo Li, Rui Liu, Qiang Hu, Jifeng Liu, Yang Yu, Yong‐Wei Zhang, Min Yang, R. Zhou, Y. Bai, Li Fei, Kai Wang, Jie Zhao, Lina Yin, Baohua Zhu, Qi Gao, Xiaoguang Guo, Bo Gao, Hui‐Yi Zeng, Tao Wen, Lin Chen, Y. L. Feng, Rong Wang, Y. Y. Guo, Ming Jin, Yangping Luo, Qi-Hui Chen, Z. J. Jiang, J. Fang, Danfeng Sun, Ning Cheng, Haoran Feng, Linlin Zhao, Xiaohong Zhao, En-Wei Liang, Chuxuan Wang, M. A. Saeed, Weiyun Xu, Zhichao Pei, Rui Yang, S. P. Zhao, S. C. Hu, R. X. Xu, Xuyang Zhou, T Yan, Jian Li, D.L Xu, Zhe Cao, W. K. Gao, X. W. Jiang, H. R. Wu, Dan Li, S. Gabici, Yi Zhang, K. J. Zhu, F. R. Zhu, I. Karpikov, C. G. Zhu, Q. W. Wu, H. L. Dai, Y. K. Hor, L. Feng, W. Mitthumsiri, Y. He, Lei Zhao, S.S Zhang, Cheng Li, C. Liu, Haifeng Zhu, Y. J. Bi, G. H. Gong, K. Jiang, Yu. V. Stenkin, S. H. Chen, Danzengluobu, A. Neronov, B. Z. Dai, T. Q. Huang, H.H He, D. H. Yan, H. B. Li, B. W. Hou, Chuyue Gao, P. Pattarakijwanich, Y. J. Wei, X. Q. Dong, K. K. Duan, W. J. Zhong, X. H. You, X. T. Feng, Y.H. Yu, L. Y. Wang, S. Q. Xi, T. X. Zeng, Y. C. Nan, X. T. Huang, S. W. Cui, Yongde Cui, N. Yin, H. N. He, J. Fang, X. L. Ji, Y. Xing, Beige Liu, L.J Ou, Z. Y. You, D. M. Wei, W. W. Tian, C. Y. Wu, Yuliang Feng, Kai Wang, Y. S. Wu
article en
16 citations

Abstract

The diffuse Galactic gamma-ray emission is a very important tool used to study the propagation and interaction of cosmic rays in the Milky Way. In this Letter, we report the measurements of the diffuse emission from the Galactic plane-covering Galactic longitudes from 15° to 235° and latitudes from -5° to +5°, in an energy range of 1 to 25 TeV-made with the Water Cherenkov Detector Array (WCDA) of the Large High Altitude Air Shower Observatory. After the sky regions of known sources are masked, the diffuse emission is detected with 24.6σ and 9.1σ significance in the inner Galactic plane (15°<l<125°, |b|<5°) and outer Galactic plane (125°<l<235°, |b|<5°), respectively. The WCDA spectra in both regions can be well described by a power-law function, with spectral indices of -2.67±0.05_{stat} in the inner region and -2.83±0.19_{stat} in the outer region, respectively. Combined with the Square Kilometer Array (KM2A) measurements at higher energies, a clear softening of the spectrum is found in the inner region, with change of spectral indices by ∼0.5 at a break energy around 30 TeV. The fluxes of the diffuse emission are higher by a factor of 1.5-2.7 than the model prediction assuming local cosmic ray spectra and the gas column density, which are consistent with those measured by the KM2A. Along the Galactic longitude, the spatial distribution of the diffuse emission shows deviation from that of the gas column density. The spectral shape of the diffuse emission may vary in different longitude regions. The WCDA measurements bridge the gap between the low-energy measurements by space detectors and the ultra-high-energy observations by KM2A and other experiments. These results suggest that improved modeling of the wideband diffuse emission is required.

Physical Review LettersVol. 134(8)
University of Science and Technology of China (CN), Dublin Institute For Advanced Studies (IE), Tibet University (CN), Nanchang University (CN), Guangxi University (CN), Moscow Institute of Physics and Technology (RU), Shandong University (CN), Sun Yat-sen University (CN), Chinese University of Hong Kong (HK), Shanghai Jiao Tong University (CN), Yunnan University (CN), Chinese Academy of Sciences (CN), Peking University (CN), Université Paris Cité (FR), Sichuan University (CN), Mahidol University (TH), Shanghai Astronomical Observatory (CN), Yunnan Observatories (CN), Purple Mountain Observatory (CN), Guangzhou University (CN), Zhengzhou University (CN), Institute for Nuclear Research (RU), National Space Science Center (CN), Zhejiang Lab (CN), Institute of High Energy Physics (CN), Max Planck Institute for Nuclear Physics (DE), National Astronomical Observatories (CN), University of Chinese Academy of Sciences (CN), Huazhong University of Science and Technology (CN), Southwest Jiaotong University (CN), China Center of Advanced Science and Technology (CN), Nanjing University (CN), Hebei Normal University (CN), Tsinghua University (CN)
National Natural Science Foundation of China, Chinese Academy of Sciences, National Science and Technology Development Agency, National Research Council of Thailand, Department of Science and Technology of Sichuan Province, National Key Research and Development Program of China, High Energy Physics
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