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

Zhen Cao^{1

2

3}, F Aharonian^{4

5}, Axikegu⁶, Y X Bai^{1

3}, Y W Bao⁷, D Bastieri⁸, X J Bi^{1

2

3}, Y J Bi^{1

3}, W Bian⁹, A V Bukevich¹⁰, Q Cao¹¹, W Y Cao¹², Zhe Cao^{12

13}, J Chang¹⁴, J F Chang^{1

3

13}, A M Chen⁹, E S Chen^{1

2

3}, H X Chen¹⁵, Liang Chen¹⁶, Lin Chen⁶, Long Chen⁶, M J Chen^{1

3}, M L Chen^{1

3

13}, Q H Chen⁶, S Chen¹⁷, S H Chen^{1

2

3}, S Z Chen^{1

3}, T L Chen¹⁸, Y Chen⁷, N Cheng^{1

3}, Y D Cheng^{1

2

3}, M C Chu¹⁹, M Y Cui¹⁴, S W Cui¹¹, X H Cui²⁰, Y D Cui²¹, B Z Dai¹⁷, H L Dai^{1

3

13}, Z G Dai¹², Danzengluobu¹⁸, X Q Dong^{1

2

3}, K K Duan¹⁴, J H Fan⁸, Y Z Fan¹⁴, J Fang¹⁷, J H Fang¹⁵, K Fang^{1

3}, C F Feng²², H Feng¹, L Feng¹⁴, S H Feng^{1

3}, X T Feng²², Y Feng¹⁵, Y L Feng¹⁸, S Gabici²³, B Gao^{1

3}, C D Gao²², Q Gao¹⁸, W Gao^{1

3}, W K Gao^{1

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3}, M M Ge¹⁷, T T Ge²¹, L S Geng^{1

3}, G Giacinti⁹, G H Gong²⁴, Q B Gou^{1

3}, M H Gu^{1

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13}, F L Guo¹⁶, J Guo²⁴, X L Guo⁶, Y Q Guo^{1

3}, Y Y Guo¹⁴, Y A Han²⁵, O A Hannuksela¹⁹, M Hasan^{1

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3}, H H He^{1

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3}, H N He¹⁴, J Y He¹⁴, Y He⁶, Y K Hor²¹, B W Hou^{1

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3}, C Hou^{1

3}, X Hou²⁶, H B Hu^{1

2

3}, Q Hu^{12

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27}, C Huang⁷, D H Huang⁶, T Q Huang^{1

3}, W J Huang²¹, X T Huang²², X Y Huang¹⁴, Y Huang^{1

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3}, Y Y Huang⁷, X L Ji^{1

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13}, H Y Jia⁶, K Jia²², H B Jiang^{1

3}, K Jiang^{12

13}, X W Jiang^{1

3}, Z J Jiang¹⁷, M Jin⁶, M M Kang²⁸, I Karpikov¹⁰, D Khangulyan^{1

3}, D Kuleshov¹⁰, K Kurinov¹⁰, B B Li¹¹, C M Li⁷, Cheng Li^{12

13}, Cong Li^{1

3}, D Li^{1

2

3}, F Li^{1

3

13}, H B Li^{1

3}, H C Li^{1

3}, Jian Li¹², Jie Li^{1

3

13}, K Li^{1

3}, S D Li^{2

16}, W L Li²², W L Li⁹, X R Li^{1

3}, Xin Li^{12

13}, Y Z Li^{1

2

3}, Zhe Li^{1

3}, Zhuo Li²⁹, E W Liang³⁰, Y F Liang³⁰, S J Lin²¹, B Liu¹², C Liu^{1

3}, D Liu²², D B Liu⁹, H Liu⁶, H D Liu²⁵, J Liu^{1

3}, J L Liu^{1

3}, M Y Liu¹⁸, R Y Liu⁷, S M Liu⁶, W Liu^{1

3}, Y Liu⁸, Y N Liu²⁴, Q Luo²¹, Y Luo⁹, H K Lv^{1

3}, B Q Ma²⁹, L L Ma^{1

3}, X H Ma^{1

3}, J R Mao²⁶, Z Min^{1

3}, W Mitthumsiri³¹, H J Mu²⁵, Y C Nan^{1

3}, A Neronov²³, K C Y Ng¹⁹, L J Ou⁸, P Pattarakijwanich³¹, Z Y Pei⁸, J C Qi^{1

2

3}, M Y Qi^{1

3}, B Q Qiao^{1

3}, J J Qin¹², A Raza^{1

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3}, D Ruffolo³¹, A Sáiz³¹, M Saeed^{1

2

3}, D Semikoz²³, L Shao¹¹, O Shchegolev^{10

32}, X D Sheng^{1

3}, F W Shu³³, H C Song²⁹, Yu V Stenkin^{10

32}, V Stepanov¹⁰, Y Su¹⁴, D X Sun^{12

14}, Q N Sun⁶, X N Sun³⁰, Z B Sun³⁴, J Takata³⁵, P H T Tam²¹, Q W Tang³³, R Tang⁹, Z B Tang^{12

13}, W W Tian^{2

20}, L H Wan²¹, C Wang³⁴, C B Wang⁶, G W Wang¹², H G Wang⁸, H H Wang²¹, J C Wang²⁶, Kai Wang⁷, Kai Wang³⁵, L P Wang^{1

2

3}, L Y Wang^{1

3}, P H Wang⁶, R Wang²², W Wang²¹, X G Wang³⁰, X Y Wang⁷, Y Wang⁶, Y D Wang^{1

3}, Y J Wang^{1

3}, Z H Wang²⁸, Z X Wang¹⁷, Zhen Wang⁹, Zheng Wang^{1

3

13}, D M Wei¹⁴, J J Wei¹⁴, Y J Wei^{1

2

3}, T Wen¹⁷, C Y Wu^{1

3}, H R Wu^{1

3}, Q W Wu³⁵, S Wu^{1

3}, X F Wu¹⁴, Y S Wu¹², S Q Xi^{1

3}, J Xia^{12

14}, G M Xiang^{2

16}, D X Xiao¹¹, G Xiao^{1

3}, Y L Xin⁶, Y Xing¹⁶, D R Xiong²⁶, Z Xiong^{1

2

3}, D L Xu⁹, R F Xu^{1

2

3}, R X Xu²⁹, W L Xu²⁸, L Xue²², D H Yan¹⁷, J Z Yan¹⁴, T Yan^{1

3}, C W Yang²⁸, C Y Yang²⁶, F Yang¹¹, F F Yang^{1

3

13}, L L Yang²¹, M J Yang^{1

3}, R Z Yang¹², W X Yang⁸, Y H Yao^{1

3}, Z G Yao^{1

3}, L Q Yin^{1

3}, N Yin²², X H You^{1

3}, Z Y You^{1

3}, Y H Yu¹², Q Yuan¹⁴, H Yue^{1

2

3}, H D Zeng¹⁴, T X Zeng^{1

3

13}, W Zeng¹⁷, M Zha^{1

3}, B B Zhang⁷, F Zhang⁶, H Zhang⁹, H M Zhang⁷, H Y Zhang¹⁷, J L Zhang²⁰, Li Zhang¹⁷, P F Zhang¹⁷, P P Zhang^{12

14}, R Zhang¹⁴, S B Zhang^{2

20}, S R Zhang¹¹, S S Zhang^{1

3}, X Zhang⁷, X P Zhang^{1

3}, Y F Zhang⁶, Yi Zhang^{1

14}, Yong Zhang^{1

3}, B Zhao⁶, J Zhao^{1

3}, L Zhao^{12

13}, L Z Zhao¹¹, S P Zhao¹⁴, X H Zhao²⁶, F Zheng³⁴, W J Zhong⁷, B Zhou^{1

3}, H Zhou⁹, J N Zhou¹⁶, M Zhou³³, P Zhou⁷, R Zhou²⁸, X X Zhou^{1

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3}, X X Zhou⁶, B Y Zhu^{12

14}, C G Zhu²², F R Zhu⁶, H Zhu²⁰, K J Zhu^{1

2

3

13}, Y C Zou³⁵, X Zuo^{1

3}; LHAASO Collaboration

Affiliations

¹ Institute of High Energy Physics, Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Chinese Academy of Sciences, 100049 Beijing, China.
² University of Chinese Academy of Sciences, 100049 Beijing, China.
³ TIANFU Cosmic Ray Research Center, Chengdu, Sichuan, China.
⁴ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, 2 Dublin, Ireland.
⁵ Max-Planck-Institut for Nuclear Physics, P.O. Box 103980, 69029 Heidelberg, Germany.
⁶ School of Physical Science and Technology & School of Information Science and Technology, Southwest Jiaotong University, 610031 Chengdu, Sichuan, China.
⁷ School of Astronomy and Space Science, Nanjing University, 210023 Nanjing, Jiangsu, China.
⁸ Center for Astrophysics, Guangzhou University, 510006 Guangzhou, Guangdong, China.
⁹ Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University, 200240 Shanghai, China.
¹⁰ Institute for Nuclear Research of Russian Academy of Sciences, 117312 Moscow, Russia.
¹¹ Hebei Normal University, 050024 Shijiazhuang, Hebei, China.
¹² University of Science and Technology of China, 230026 Hefei, Anhui, China.
¹³ State Key Laboratory of Particle Detection and Electronics, China.
¹⁴ Key Laboratory of Dark Matter and Space Astronomy & Key Laboratory of Radio Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, 210023 Nanjing, Jiangsu, China.
¹⁵ Research Center for Astronomical Computing, Zhejiang Laboratory, 311121 Hangzhou, Zhejiang, China.
¹⁶ Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 200030 Shanghai, China.
¹⁷ School of Physics and Astronomy, Yunnan University, 650091 Kunming, Yunnan, China.
¹⁸ Key Laboratory of Cosmic Rays (Tibet University), Ministry of Education, 850000 Lhasa, Tibet, China.
¹⁹ Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
²⁰ Key Laboratory of Radio Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, 100101 Beijing, China.
²¹ School of Physics and Astronomy (Zhuhai) & School of Physics (Guangzhou) & Sino-French Institute of Nuclear Engineering and Technology (Zhuhai), Sun Yat-sen University, 519000 Zhuhai & 510275 Guangzhou, Guangdong, China.
²² Institute of Frontier and Interdisciplinary Science, Shandong University, 266237 Qingdao, Shandong, China.
²³ APC, Université Paris Cité, CNRS/IN2P3, CEA/IRFU, Observatoire de Paris, 119 75205 Paris, France.
²⁴ Department of Engineering Physics & Department of Astronomy, Tsinghua University, 100084 Beijing, China.
²⁵ School of Physics and Microelectronics, Zhengzhou University, 450001 Zhengzhou, Henan, China.
²⁶ Yunnan Observatories, Chinese Academy of Sciences, 650216 Kunming, Yunnan, China.
²⁷ China Center of Advanced Science and Technology, Beijing 100190, China.
²⁸ College of Physics, Sichuan University, 610065 Chengdu, Sichuan, China.
²⁹ School of Physics, Peking University, 100871 Beijing, China.
³⁰ Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University, 530004 Nanning, Guangxi, China.
³¹ Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.
³² Moscow Institute of Physics and Technology, 141700 Moscow, Russia.
³³ Center for Relativistic Astrophysics and High Energy Physics, School of Physics and Materials Science and Institute of Space Science and Technology, Nanchang University, 330031 Nanchang, Jiangxi, China.
³⁴ National Space Science Center, Chinese Academy of Sciences, 100190 Beijing, China.
³⁵ School of Physics, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China.

PMID: 40085904
DOI: 10.1103/PhysRevLett.134.081002

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

Zhen Cao et al. Phys Rev Lett. 2025.

. 2025 Feb 28;134(8):081002.

doi: 10.1103/PhysRevLett.134.081002.

Authors

Affiliations

¹ Institute of High Energy Physics, Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Chinese Academy of Sciences, 100049 Beijing, China.
² University of Chinese Academy of Sciences, 100049 Beijing, China.
³ TIANFU Cosmic Ray Research Center, Chengdu, Sichuan, China.
⁴ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, 2 Dublin, Ireland.
⁵ Max-Planck-Institut for Nuclear Physics, P.O. Box 103980, 69029 Heidelberg, Germany.
⁶ School of Physical Science and Technology & School of Information Science and Technology, Southwest Jiaotong University, 610031 Chengdu, Sichuan, China.
⁷ School of Astronomy and Space Science, Nanjing University, 210023 Nanjing, Jiangsu, China.
⁸ Center for Astrophysics, Guangzhou University, 510006 Guangzhou, Guangdong, China.
⁹ Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University, 200240 Shanghai, China.
¹⁰ Institute for Nuclear Research of Russian Academy of Sciences, 117312 Moscow, Russia.
¹¹ Hebei Normal University, 050024 Shijiazhuang, Hebei, China.
¹² University of Science and Technology of China, 230026 Hefei, Anhui, China.
¹³ State Key Laboratory of Particle Detection and Electronics, China.
¹⁴ Key Laboratory of Dark Matter and Space Astronomy & Key Laboratory of Radio Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, 210023 Nanjing, Jiangsu, China.
¹⁵ Research Center for Astronomical Computing, Zhejiang Laboratory, 311121 Hangzhou, Zhejiang, China.
¹⁶ Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 200030 Shanghai, China.
¹⁷ School of Physics and Astronomy, Yunnan University, 650091 Kunming, Yunnan, China.
¹⁸ Key Laboratory of Cosmic Rays (Tibet University), Ministry of Education, 850000 Lhasa, Tibet, China.
¹⁹ Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
²⁰ Key Laboratory of Radio Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, 100101 Beijing, China.
²¹ School of Physics and Astronomy (Zhuhai) & School of Physics (Guangzhou) & Sino-French Institute of Nuclear Engineering and Technology (Zhuhai), Sun Yat-sen University, 519000 Zhuhai & 510275 Guangzhou, Guangdong, China.
²² Institute of Frontier and Interdisciplinary Science, Shandong University, 266237 Qingdao, Shandong, China.
²³ APC, Université Paris Cité, CNRS/IN2P3, CEA/IRFU, Observatoire de Paris, 119 75205 Paris, France.
²⁴ Department of Engineering Physics & Department of Astronomy, Tsinghua University, 100084 Beijing, China.
²⁵ School of Physics and Microelectronics, Zhengzhou University, 450001 Zhengzhou, Henan, China.
²⁶ Yunnan Observatories, Chinese Academy of Sciences, 650216 Kunming, Yunnan, China.
²⁷ China Center of Advanced Science and Technology, Beijing 100190, China.
²⁸ College of Physics, Sichuan University, 610065 Chengdu, Sichuan, China.
²⁹ School of Physics, Peking University, 100871 Beijing, China.
³⁰ Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University, 530004 Nanning, Guangxi, China.
³¹ Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.
³² Moscow Institute of Physics and Technology, 141700 Moscow, Russia.
³³ Center for Relativistic Astrophysics and High Energy Physics, School of Physics and Materials Science and Institute of Space Science and Technology, Nanchang University, 330031 Nanchang, Jiangxi, China.
³⁴ National Space Science Center, Chinese Academy of Sciences, 100190 Beijing, China.
³⁵ School of Physics, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China.

PMID: 40085904
DOI: 10.1103/PhysRevLett.134.081002

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.

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

Affiliations

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

Authors

Affiliations

Abstract

LinkOut - more resources

Full Text Sources

Miscellaneous