Evidence for particle acceleration approaching PeV energies in the W51 complex
Abstract
The -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 rays emanating from the W51 complex, with energies from 2 TeV to 200 TeV. The LHAASO measurements, for the first time, extend the -ray emission from the W51 complex beyond 100 TeV and reveal a significant spectrum bending at tens of TeV. By combining the ``-decay bump" featured data from Fermi-LAT, the broadband -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 ~TeV or a power-law break at ~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 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.
Cite
@article{arxiv.2407.00624,
title = {Evidence for particle acceleration approaching PeV energies in the W51 complex},
author = {The LHAASO Collaboration and Zhen Cao and F. Aharonian and Axikegu and Y. X. Bai and Y. W. Bao and D. Bastieri and X. J. Bi and Y. J. Bi and W. Bian and A. V. Bukevich and Q. Cao and W. Y. Cao and Zhe Cao and J. Chang and J. F. Chang and M. Chen and E. S. Chen and H. X. Chen and Liang Chen and Lin Chen and Long Chen and M. J. Chen and M. L. Chen and Q. H. Chen and S. Chen and S. H. Chen and S. Z. Chen and T. L. Chen and Y. Chen and N. Cheng and Y. D. Cheng and M. Y. Cui and S. W. Cui and X. H. Cui and Y. D. Cui and B. Z. Dai and H. L. Dai and Z. G. Dai and Danzengluobu and X. Q. Dong and K. K. Duan and J. H. Fan and Y. Z. Fan and J. Fang and J. H. Fang and K. Fang and C. F. Feng and H. Feng and L. Feng and S. H. Feng and X. T. Feng and Y. Feng and Y. L. Feng and S. Gabici and B. Gao and C. D. Gao and Q. Gao and W. Gao and W. K. Gao and M. M. Ge and L. S. Geng and G. Giacinti and G. H. Gong and Q. B. Gou and M. H. Gu and F. L. Guo and X. L. Guo and Y. Q. Guo and Y. Y. Guo and Y. A. Han and M. Hasan and H. H. He and H. N. He and J. Y. He and Y. He and Y. K. Hor and B. W. Hou and C. Hou and X. Hou and H. B. Hu and Q. Hu and S. C. Hu and D. H. Huang and T. Q. Huang and W. J. Huang and X. T. Huang and X. Y. Huang and Y. Huang and X. L. Ji and H. Y. Jia and K. Jia and K. Jiang and X. W. Jiang and Z. J. Jiang and M. Jin and M. M. Kang and I. Karpikov and D. Kuleshov and K. Kurinov and B. B. Li and C. M. Li and Cheng Li and Cong Li and D. Li and F. Li and H. B. Li and H. C. Li and Jian Li and Jie Li and K. Li and S. D. Li and W. L. Li and W. L. Li and X. R. Li and Xin Li and Y. Z. Li and Zhe Li and Zhuo Li and E. W. Liang and Y. F. Liang and S. J. Lin and B. Liu and C. Liu and D. Liu and D. B. Liu and H. Liu and H. D. Liu and J. Liu and J. L. Liu and M. Y. Liu and R. Y. Liu and S. M. Liu and W. Liu and Y. Liu and Y. N. Liu and Q. Luo and Y. Luo and H. K. Lv and B. Q. Ma and L. L. Ma and X. H. Ma and J. R. Mao and Z. Min and W. Mitthumsiri and H. J. Mu and Y. C. Nan and A. Neronov and L. J. Ou and P. Pattarakijwanich and Z. Y. Pei and J. C. Qi and M. Y. Qi and B. Q. Qiao and J. J. Qin and A. Raza and D. Ruffolo and A. Sáiz and M. Saeed and D. Semikoz and L. Shao and O. Shchegolev and X. D. Sheng and F. W. Shu and H. C. Song and Yu. V. Stenkin and V. Stepanov and Y. Su and D. X. Sun and Q. N. Sun and X. N. Sun and Z. B. Sun and J. Takata and P. H. T. Tam and Q. W. Tang and R. Tang and Z. B. Tang and W. W. Tian and C. Wang and C. B. Wang and G. W. Wang and H. G. Wang and H. H. Wang and J. C. Wang and Kai Wang and Kai Wang and L. P. Wang and L. Y. Wang and P. H. Wang and R. Wang and W. Wang and X. G. Wang and X. Y. Wang and Y. Wang and Y. D. Wang and Y. J. Wang and Z. H. Wang and Z. X. Wang and Zhen Wang and Zheng Wang and D. M. Wei and J. J. Wei and Y. J. Wei and T. Wen and C. Y. Wu and H. R. Wu and Q. W. Wu and S. Wu and X. F. Wu and Y. S. Wu and S. Q. Xi and J. Xia and G. M. Xiang and D. X. Xiao and G. Xiao and Y. L. Xin and Y. Xing and D. R. Xiong and Z. Xiong and D. L. Xu and R. F. Xu and R. X. Xu and W. L. Xu and L. Xue and D. H. Yan and J. Z. Yan and T. Yan and C. W. Yang and C. Y. Yang and F. Yang and F. F. Yang and L. L. Yang and M. J. Yang and R. Z. Yang and W. X. Yang and Y. H. Yao and Z. G. Yao and L. Q. Yin and N. Yin and X. H. You and Z. Y. You and Y. H. Yu and Q. Yuan and H. Yue and H. D. Zeng and T. X. Zeng and W. Zeng and M. Zha and B. B. Zhang and F. Zhang and H. Zhang and H. M. Zhang and H. Y. Zhang and J. L. Zhang and Li Zhang and P. F. Zhang and P. P. Zhang and R. Zhang and S. B. Zhang and S. R. Zhang and S. S. Zhang and X. Zhang and X. P. Zhang and Y. F. Zhang and Yi Zhang and Yong Zhang and B. Zhao and J. Zhao and L. Zhao and L. Z. Zhao and S. P. Zhao and X. H. Zhao and F. Zheng and W. J. Zhong and B. Zhou and H. Zhou and J. N. Zhou and M. Zhou and P. Zhou and R. Zhou and X. X. Zhou and X. X. Zhou and B. Y. Zhu and C. G. Zhu and F. R. Zhu and H. Zhu and K. J. Zhu and Y. C. Zou and X. Zuo and S. Celli},
journal= {arXiv preprint arXiv:2407.00624},
year = {2026}
}