Evidence for particle acceleration approaching PeV energies in the W51 complex

LHAASO Collaboration. Electronic address: fangkun@ihep.ac.cn; LHAASO Collaboration

doi:10.1016/j.scib.2024.07.017

Evidence for particle acceleration approaching PeV energies in the W51 complex

Sci Bull (Beijing). 2024 Sep 30;69(18):2833-2841. doi: 10.1016/j.scib.2024.07.017. Epub 2024 Jul 16.

Authors

LHAASO Collaboration. Electronic address: [email protected]; LHAASO Collaboration

Collaborators

Zhen Cao¹, F Aharonian², Axikegu³, Y X Bai⁴, Y W Bao⁵, D Bastieri⁶, X J Bi¹, Y J Bi⁴, W Bian⁷, A V Bukevich⁸, Q Cao⁹, W Y Cao¹⁰, Zhe Cao¹¹, J Chang¹², J F Chang¹³, A M Chen⁷, E S Chen¹, H X Chen¹⁴, Liang Chen¹⁵, Lin Chen³, Long Chen³, M J Chen⁴, M L Chen¹³, Q H Chen³, S Chen¹⁶, S H Chen¹, S Z Chen⁴, T L Chen¹⁷, Y Chen⁵, N Cheng⁴, Y D Cheng¹, M Y Cui¹², S W Cui⁹, X H Cui¹⁸, Y D Cui¹⁹, B Z Dai¹⁶, H L Dai¹³, Z G Dai¹⁰, Danzengluobu¹⁷, X Q Dong¹, K K Duan¹², J H Fan⁶, Y Z Fan¹², J Fang¹⁶, J H Fang¹⁴, K Fang²⁰, C F Feng²¹, H Feng²², L Feng¹², S H Feng⁴, X T Feng²¹, Y Feng¹⁴, Y L Feng¹⁷, S Gabici²³, B Gao⁴, C D Gao²¹, Q Gao¹⁷, W Gao⁴, W K Gao¹, M M Ge¹⁶, L S Geng⁴, G Giacinti⁷, G H Gong²⁴, Q B Gou⁴, M H Gu¹³, F L Guo¹⁵, X L Guo³, Y Q Guo⁴, Y Y Guo¹², Y A Han²⁵, M Hasan¹, H H He¹, H N He¹², J Y He¹², Y He³, Y K Hor¹⁹, B W Hou¹, C Hou⁴, X Hou²⁶, H B Hu¹, Q Hu²⁷, S C Hu²⁸, D H Huang³, T Q Huang⁴, W J Huang¹⁹, X T Huang²¹, X Y Huang¹², Y Huang¹, X L Ji¹³, H Y Jia³, K Jia²¹, K Jiang¹¹, X W Jiang⁴, Z J Jiang¹⁶, M Jin³, M M Kang²⁹, I Karpikov⁸, D Kuleshov⁸, K Kurinov⁸, B B Li⁹, C M Li⁵, Cheng Li¹¹, Cong Li⁴, D Li¹, F Li¹³, H B Li⁴, H C Li⁴, Jian Li¹⁰, Jie Li¹³, K Li⁴, S D Li³⁰, W L Li²¹, W L Li⁷, X R Li⁴, Xin Li¹¹, Y Z Li¹, Zhe Li³¹, Zhuo Li³², E W Liang³³, Y F Liang³³, S J Lin¹⁹, B Liu¹⁰, C Liu³⁴, D Liu²¹, D B Liu⁷, H Liu³, H D Liu²⁵, J Liu⁴, J L Liu⁴, M Y Liu¹⁷, R Y Liu⁵, S M Liu³, W Liu⁴, Y Liu⁶, Y N Liu²⁴, Q Luo¹⁹, Y Luo⁷, H K Lv⁴, B Q Ma³², L L Ma⁴, X H Ma⁴, J R Mao²⁶, Z Min⁴, W Mitthumsiri³⁵, H J Mu²⁵, Y C Nan⁴, A Neronov²³, L J Ou⁶, P Pattarakijwanich³⁵, Z Y Pei⁶, J C Qi¹, M Y Qi⁴, B Q Qiao⁴, J J Qin¹⁰, A Raza¹, D Ruffolo³⁵, A Sáiz³⁵, M Saeed¹, D Semikoz²³, L Shao⁹, O Shchegolev³⁶, X D Sheng⁴, F W Shu³⁷, H C Song³², Yu V Stenkin³⁶, V Stepanov⁸, Y Su¹², D X Sun²⁷, Q N Sun³, X N Sun³³, Z B Sun³⁸, J Takata³⁹, P H T Tam¹⁹, Q W Tang³⁷, R Tang⁷, Z B Tang¹¹, W W Tian⁴⁰, C Wang³⁸, C B Wang³, G W Wang¹⁰, H G Wang⁶, H H Wang¹⁹, J C Wang²⁶, Kai Wang⁵, Kai Wang³⁹, L P Wang¹, L Y Wang⁴, P H Wang³, R Wang²¹, W Wang¹⁹, X G Wang³³, X Y Wang⁵, Y Wang³, Y D Wang⁴, Y J Wang⁴, Z H Wang²⁹, Z X Wang¹⁶, Zhen Wang⁷, Zheng Wang¹³, D M Wei¹², J J Wei¹², Y J Wei¹, T Wen¹⁶, C Y Wu⁴, H R Wu⁴, Q W Wu³⁹, S Wu⁴, X F Wu¹², Y S Wu¹⁰, S Q Xi⁴, J Xia²⁷, G M Xiang³⁰, D X Xiao⁹, G Xiao⁴, Y L Xin³, Y Xing¹⁵, D R Xiong²⁶, Z Xiong¹, D L Xu⁷, R F Xu¹, R X Xu³², W L Xu²⁹, L Xue²¹, D H Yan¹⁶, J Z Yan¹², T Yan⁴, C W Yang²⁹, C Y Yang²⁶, F Yang⁹, F F Yang¹³, L L Yang¹⁹, M J Yang⁴, R Z Yang¹⁰, W X Yang⁶, Y H Yao⁴, Z G Yao⁴, L Q Yin⁴, N Yin²¹, X H You⁴, Z Y You⁴, Y H Yu¹⁰, Q Yuan¹², H Yue¹, H D Zeng¹², T X Zeng¹³, W Zeng¹⁶, M Zha⁴, B B Zhang⁵, F Zhang³, H Zhang⁷, H M Zhang⁵, H Y Zhang⁴, J L Zhang¹⁸, Li Zhang¹⁶, P F Zhang¹⁶, P P Zhang²⁷, R Zhang²⁷, S B Zhang⁴⁰, S R Zhang⁹, S S Zhang⁴, X Zhang⁵, X P Zhang⁴, Y F Zhang³, Yi Zhang⁴¹, Yong Zhang⁴, B Zhao³, J Zhao⁴, L Zhao¹¹, L Z Zhao⁹, S P Zhao¹², X H Zhao²⁶, F Zheng³⁸, W J Zhong⁵, B Zhou⁴, H Zhou⁷, J N Zhou¹⁵, M Zhou³⁷, P Zhou⁵, R Zhou²⁹, X X Zhou¹, X X Zhou³, B Y Zhu²⁷, C G Zhu²¹, F R Zhu³, H Zhu¹⁸, K J Zhu⁴², Y C Zou³⁹, X Zuo⁴, S Celli⁴³

Affiliations

¹ Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; University of Chinese Academy of Sciences, Beijing 100049, China; TIANFU Cosmic Ray Research Center, Chengdu, China.
² Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, 2 Dublin, Ireland; Max-Planck-Institut for Nuclear Physics, P.O. Box 103980, Heidelberg 69029, Germany.
³ School of Physical Science and Technology & School of Information Science and Technology, Southwest Jiaotong University, Chengdu 610031, China.
⁴ Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; TIANFU Cosmic Ray Research Center, Chengdu, China.
⁵ School of Astronomy and Space Science, Nanjing University, Nanjing 210023, China.
⁶ Center for Astrophysics, Guangzhou University, Guangzhou 510006, China.
⁷ Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China.
⁸ Institute for Nuclear Research of Russian Academy of Sciences, Moscow 117312, Russia.
⁹ Hebei Normal University, Shijiazhuang 050024, China.
¹⁰ University of Science and Technology of China, Hefei 230026, China.
¹¹ State Key Laboratory of Particle Detection and Electronics, China; University of Science and Technology of China, Hefei 230026, China.
¹² Key Laboratory of Dark Matter and Space Astronomy & Key Laboratory of Radio Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China.
¹³ Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; TIANFU Cosmic Ray Research Center, Chengdu, China; State Key Laboratory of Particle Detection and Electronics, China.
¹⁴ Research Center for Astronomical Computing, Zhejiang Laboratory, Hangzhou 311121, China.
¹⁵ Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China.
¹⁶ School of Physics and Astronomy, Yunnan University, Kunming 650091, China.
¹⁷ Key Laboratory of Cosmic Rays (Tibet University), Ministry of Education, Lhasa 850000, China.
¹⁸ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China.
¹⁹ School of Physics and Astronomy (Zhuhai) & School of Physics (Guangzhou) & Sino-French Institute of Nuclear Engineering and Technology (Zhuhai), Sun Yat-sen University, Zhuhai 519000 & Guangzhou 510275, Guangdong, China.
²⁰ Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; TIANFU Cosmic Ray Research Center, Chengdu, China. Electronic address: [email protected].
²¹ Institute of Frontier and Interdisciplinary Science, Shandong University, Qingdao 266237, China.
²² Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
²³ APC, Université Paris Cité, CNRS/IN2P3, CEA/IRFU, Observatoire de Paris, Paris 119 75205, France.
²⁴ Department of Engineering Physics, Tsinghua University, Beijing 100084, China.
²⁵ School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450001, China.
²⁶ Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, China.
²⁷ University of Science and Technology of China, Hefei 230026, China; Key Laboratory of Dark Matter and Space Astronomy & Key Laboratory of Radio Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China.
²⁸ Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; TIANFU Cosmic Ray Research Center, Chengdu, China; China Center of Advanced Science and Technology, Beijing 100190, China.
²⁹ College of Physics, Sichuan University, Chengdu 610065, China.
³⁰ Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China; University of Chinese Academy of Sciences, Beijing 100049, China.
³¹ Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; TIANFU Cosmic Ray Research Center, Chengdu, China. Electronic address: [email protected].
³² School of Physics, Peking University, Beijing 100871, China.
³³ Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University, Nanning 530004, China.
³⁴ Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; TIANFU Cosmic Ray Research Center, Chengdu, China. Electronic address: [email protected].
³⁵ Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.
³⁶ Institute for Nuclear Research of Russian Academy of Sciences, Moscow 117312, Russia; Moscow Institute of Physics and Technology, Moscow 141700, Russia.
³⁷ Center for Relativistic Astrophysics and High Energy Physics, School of Physics and Materials Science & Institute of Space Science and Technology, Nanchang University, Nanchang 330031, China.
³⁸ National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China.
³⁹ School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China.
⁴⁰ University of Chinese Academy of Sciences, Beijing 100049, China; National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China.
⁴¹ Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; Key Laboratory of Dark Matter and Space Astronomy & Key Laboratory of Radio Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China.
⁴² Key Laboratory of Particle Astrophysics & Experimental Physics Division & Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; University of Chinese Academy of Sciences, Beijing 100049, China; TIANFU Cosmic Ray Research Center, Chengdu, China; State Key Laboratory of Particle Detection and Electronics, China.
⁴³ Department of Physics, Sapienza University of Rome, Piazzale Aldo Moro 2, Rome 00185, Italy. Electronic address: [email protected].

PMID: 39153903
DOI: 10.1016/j.scib.2024.07.017

Abstract

The γ-ray emission from the W51 complex is widely acknowledged to be attributed to the interaction between the cosmic rays (CRs) accelerated by the shock of supernova remnant (SNR) W51C and the dense molecular clouds in the adjacent star-forming region, W51B. However, the maximum acceleration capability of W51C for CRs remains elusive. Based on observations conducted with the Large High Altitude Air Shower Observatory (LHAASO), we report a significant detection of γ rays emanating from the W51 complex, with energies from 2 to 200 TeV. The LHAASO measurements, for the first time, extend the γ-ray emission from the W51 complex beyond 100 TeV and reveal a significant spectrum bending at tens of TeV. By combining the "π⁰-decay bump" featured data from Fermi-LAT, the broadband γ-ray spectrum of the W51 region can be well-characterized by a simple pp-collision model. The observed spectral bending feature suggests an exponential cutoff at ∼400 TeV or a power-law break at ∼200 TeV in the CR proton spectrum, most likely providing the first evidence of SNRs serving as CR accelerators approaching the PeV regime. Additionally, two young star clusters within W51B could also be theoretically viable to produce the most energetic γ rays observed by LHAASO. Our findings strongly support the presence of extreme CR accelerators within the W51 complex and provide new insights into the origin of Galactic CRs.

Keywords: Cosmic rays; SNR W51C; Star clusters; UHE -ray.