Does or Did the Supernova Remnant Cassiopeia A Operate as a PeVatron?

Zhen Cao,F Aharonian,Q An,Axikegu Axikegu,Y X Bai,Y W Bao,D Bastieri,X J Bi,Y J Bi,J T Cai,Q Cao,W Y Cao,Zhe Cao,J Chang,J F Chang,A M Chen,E S Chen,Liang Chen,Lin Chen,Long Chen,M J Chen,M L Chen,Q H Chen,S H Chen,S Z Chen,T L Chen,Y Chen,N 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 Danzengluobu,D Della Volpe,X Q Dong,K K Duan,J H Fan,Y Z Fan,J Fang,K Fang,C F Feng,L Feng,S H Feng,X T Feng,Y L Feng,S Gabici,B Gao,C D Gao,L Q Gao,Q Gao,W Gao,W K Gao,M M Ge,L S Geng,G Giacinti,G H Gong,Q B Gou,M H Gu,F L Guo,X L Guo,Y Q Guo,Y Y Guo,Y A Han,H H He,H N He,J Y He,X B He,Y He,M Heller,Y K Hor,B W Hou,C Hou,X Hou,H B Hu,Q Hu,S C Hu,D H Huang,T Q Huang,W J Huang,X T Huang,X Y Huang,Y Huang,Z C Huang,X L Ji,H Y Jia,K Jia,K Jiang,X W Jiang,Z J Jiang,M Jin,M M Kang,T Ke,D Kuleshov,K Kurinov,B B Li,Cheng Li,Cong Li,D Li,F Li,H B Li,H C Li,H Y Li,J Li,Jian Li,Jie Li,K Li,W L Li,X R Li,Xin Li,Y Z Li,Zhe Li,Zhuo Li,E W Liang,Y F Liang,S J Lin,B Liu,C Liu,D Liu,H Liu,H D Liu,J Liu,J L Liu,J Y Liu,M Y Liu,R Y Liu,S M Liu,W Liu,Y Liu,Y N Liu,R Lu,Q Luo,H K Lv,B Q Ma,L L Ma,X H Ma,J R Mao,Z Min,W Mitthumsiri,H J Mu,Y C Nan,A Neronov,Z W Ou,B Y Pang,P Pattarakijwanich,Z Y Pei,M Y Qi,Y Q Qi,B Q Qiao,J J Qin,D Ruffolo,A Sáiz,D Semikoz,C Y Shao,L Shao,O Shchegolev,X D Sheng,F W Shu,H C Song,Yu V Stenkin,V Stepanov,Y Su,Q N Sun,X N Sun,Z B Sun,P H T Tam,Q W Tang,Z B Tang,W W Tian,C Wang,C B Wang,G W Wang,H G Wang,H H Wang,J C Wang,K Wang,L P Wang,L Y Wang,P H Wang,R Wang,W Wang,X G Wang,X Y Wang,Y Wang,Y D Wang,Y J Wang,Z H Wang,Z X Wang,Zhen Wang,Zheng Wang,D M Wei,J J Wei,Y J Wei,T Wen,C Y Wu,H R 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,G G Xin,Y L Xin,Y Xing,Z Xiong,D L Xu,R F Xu,R X Xu,W L Xu,L Xue,D H Yan,J Z Yan,T Yan,C W Yang,F Yang,F F Yang,H W Yang,J Y Yang,L L Yang,M J Yang,R Z Yang,S B Yang,Y H Yao,Z G Yao,Y M Ye,L Q Yin,N Yin,X H You,Z Y You,Y H Yu,Q Yuan,H Yue,H D Zeng,T X Zeng,W Zeng,M Zha,B B Zhang,F Zhang,H M Zhang,H Y Zhang,J L Zhang,L X Zhang,Li Zhang,P F Zhang,P P Zhang,R Zhang,S B Zhang,S R Zhang,S S Zhang,X Zhang,X P Zhang,Y F Zhang,Yi Zhang,Yong Zhang,B Zhao,J Zhao,L Zhao,L Z Zhao,S P Zhao,F Zheng,B Zhou,H Zhou,J N Zhou,M Zhou,P Zhou,R Zhou,X X Zhou,C G Zhu,F R Zhu,H Zhu,K J Zhu,X Zuo

doi:10.3847/2041-8213/ad1d62

Abstract

For decades, supernova remnants (SNRs) have been considered the prime sources of Galactic cosmic rays (CRs). But whether SNRs can accelerate CR protons to PeV energies and thus dominate CR flux up to the knee is currently under intensive theoretical and phenomenological debate. The direct test of the ability of SNRs to operate as CR PeVatrons can be provided by ultrahigh-energy (UHE; E γ ≥ 100 TeV) γ-rays. In this context, the historical SNR Cassiopeia A (Cas A) is considered one of the most promising targets for UHE observations. This paper presents the observation of Cas A and its vicinity by the LHAASO KM2A detector. The exceptional sensitivity of LHAASO KM2A in the UHE band, combined with the young age of Cas A, enabled us to derive stringent model-independent limits on the energy budget of UHE protons and nuclei accelerated by Cas A at any epoch after the explosion. The results challenge the prevailing paradigm that Cas A–type SNRs are major suppliers of PeV CRs in the Milky Way.

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