Cygnus X-3: A variable petaelectronvolt gamma-ray source

The LHAASO Collaboration , Zhen Cao , F. Aharonian , Y.X. Bai , Y.W. Bao , D. Bastieri , X.J. Bi , Y.J. Bi

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W. Bian J. Blunier A.V. Bukevich C.M. Cai Y.Y. Cai W.Y. Cao Zhe Cao J. Chang J.F. Chang E.S. Chen G.H. Chen H.K. Chen L.F. 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 X.P. Chen Y. Chen N. Cheng Q.Y. Cheng Y.D. Cheng 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 A.J. Dong 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 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 K.J. Guo X.L. Guo Y.Q. Guo Y.Y. Guo R.P. Han O.A. Hannuksela M. Hasan H.H. He H.N. He J.Y. He X.Y. He Y. He S. Hern\'andez-Cadena B.W. Hou C. Hou X. Hou H.B. Hu S.C. Hu C. Huang D.H. Huang J.J. Huang X.L. Huang X.T. Huang X.Y. Huang Y. Huang Y.Y. Huang A. Inventar 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 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 Zhe Li Zhuo Li E.W. Liang Y.F. Liang S.J. Lin B. Liu C. Liu D. Liu D.B. Liu H. 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 I.O. Maliy J.R. Mao Z. Min W. Mitthumsiri Y. Mizuno G.B. Mou A. Neronov K.C.Y. Ng M.Y. Ni L. Nie L.J. Ou Z.W. Ou P. Pattarakijwanich Z.Y. Pei D.Y. Peng J.C. Qi M.Y. Qi J.J. Qin D. Qu A. Raza C.Y. Ren D. Ruffolo A. S\'aiz D. Savchenko 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 J.X. 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 D.H. 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.F. Xiao Y.L. Xin H.D. Xing Y. Xing D.R. Xiong B.N. Xu C.Y. Xu D.L. Xu R.F. Xu R.X. Xu S.S. 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 H. Zhang H.M. Zhang H.Y. Zhang J.L. Zhang J.Y. Zhang Li Zhang P.F. Zhang R. Zhang S.R. Zhang S.S. Zhang S.Y. Zhang W. 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 T.C. Zheng 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 (The LHAASO Collaboration) J.S.Wang

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keywords gammasigmabinarycygnusdetectedenergygamma-rayhigh

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We report the discovery of variable $\gamma$-rays up to petaelectronvolt from Cygnus X-3, an iconic X-ray binary. The $\gamma$-ray signal was detected with a statistical significance of approximately 10 $\sigma$ by the Large High Altitude Air Shower Observatory (LHAASO). Its intrinsic spectral energy distribution (SED), extending from 0.06 to 3.7 PeV, shows a pronounced rise toward 1 PeV after accounting for absorption by the cosmic microwave background radiation. We find variability on month-long timescales at a significance of $8.6 \sigma$, coinciding with a high state of the GeV gamma-ray flux detected by the Fermi-LAT. This,together with a 3.2$\sigma$ evidence for orbital modulation, suggests that the PeV $\gamma$-rays originate within, or in close proximity to, the binary system itself. The observed energy spectrum and temporal modulation can be naturally explained by $\gamma$-ray production through photomeson processes in the innermost region of the relativistic jet, where protons need to be accelerated to tens of PeV energies.

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