Detection of two TeV gamma-ray outbursts from NGC 1275 by LHAASO
Authors: Cao Zhen , Aharonian F , Axikegu  , Bai Y X , Bao Y W , Bastieri D , Bi X J , Bi Y J , Bian W , Bukevich A V , Cao Q , Cao W Y , Cao Zhe , Chang J , Chang J F , Chen A M , Chen E S , Chen H X , Chen Liang , Chen Lin , Chen Long , Chen M J , Chen M L , Chen Q H , Chen S , Chen S H , Chen S Z , Chen T L , Chen Y , Cheng N , Cheng Y D , Chu M C , Cui M Y , Cui S W , Cui X H , Cui Y D , Dai B Z , Dai H L , Dai Z G , Danzengluobu  , Dong X Q , Duan K K , Fan J H , Fan Y Z , Fang J , Fang J H , Fang K , Feng C F , Feng H , Feng L , Feng S H , Feng X T , Feng Y , Feng Y L , Gabici S , Gao B , Gao C D , Gao Q , Gao W , Gao W K , Ge M M , Ge T T , Geng L S , Giacinti G , Gong G H , Gou Q B , Gu M H , Guo F L , Guo J , Guo X L , Guo Y Q , Guo Y Y , Han Y A , Hannuksela O A , Hasan M , He H H , He H N , He J Y , He Y , Hor Y K , Hou B W , Hou C , Hu H B , Hu Q , Hu S C , Huang C , Huang D H , Huang T Q , Huang W J , Huang X T , Huang X Y , Huang Y , Huang Y Y , Ji X L , Jia H Y , Jia K , Jiang H B , Jiang K , Jiang X W , Jiang Z J , Jin M , Kang M M , Karpikov I , Khangulyan D , Kuleshov D , Kurinov K , Li B B , Li C M , Li Cheng , Li Cong , Li D , Li F , Li H B , Li H C , Li Jian , Li Jie , Li K , Li S D , Li W L , Li W L , Li X R , Li Xin , Li Y Z , Li Zhe , Li Zhuo , Liang E W , Liang Y F , Lin S J , Liu B , Liu C , Liu D , Liu D B , Liu H , Liu H D , Liu J , Liu J L , Liu M Y , Liu R Y , Liu S M , Liu W , Liu Y , Liu Y N , Luo Q , Luo Y , Lv H K , Ma B Q , Ma L L , Ma X H , Mao J R , Min Z , Mitthumsiri W , Mu H J , Nan Y C , Neronov A , Ng K C Y , Ou L J , Pattarakijwanich P , Pei Z Y , Qi J C , Qi M Y , Qiao B Q , Qin J J , Raza A , Ruffolo D , Sáiz A , Saeed M , Semikoz D , Shao L , Shchegolev O , Sheng X D , Shu F W , Song H C , Stenkin Yu V , Stepanov V , Su Y , Sun D X , Sun Q N , Sun X N , Sun Z B , Takata J , Tam P H T , Tang Q W , Tang R , Tang Z B , Tian W W , Wan L H , Wang C , Wang C B , Wang G W , Wang H G , Wang H H , Wang J C , Wang Kai , Wang Kai , 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 , Wei D M , Wei J J , Wei Y J , Wen T , Wu C Y , Wu H R , Wu Q W , Wu S , Wu X F , Wu Y S , Xi S Q , Xia J , Xiang G M , Xiao D X , Xiao G , Xin Y L , Xing Y , Xiong D R , Xiong Z , Xu D L , Xu R F , Xu R X , Xu W L , Xue L , Yan D H , Yan J Z , Yan T , Yang C W , Yang C Y , Yang F , Yang F F , Yang L L , Yang M J , Yang R Z , Yang W X , Yao Y H , Yao Z G , Yin L Q , Yin N , You X H , You Z Y , Yu Y H , Yuan Q , Yue H , Zeng H D , Zeng T X , Zeng W , Zha M , Zhang B B , Zhang F , Zhang H , Zhang H M , Zhang H Y , Zhang J L , 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 , Zhao B , Zhao J , Zhao L , Zhao L Z , Zhao S P , Zhao X H , Zheng F , Zhong W J , Zhou B , Zhou H , Zhou J N , Zhou M , Zhou P , Zhou R , Zhou X X , Zhou X X , Zhu B Y , Zhu C G , Zhu F R , Zhu H , Zhu K J , Zou Y C , Zuo X 
Published: November 2024

The Water Cherenkov Detector Array (WCDA) is one of the components of Large High Altitude Air Shower Observatory (LHAASO) and can monitor any sources over two-thirds of the sky for up to 7 hours per day with &gt;98% duty cycle. In this work, we report the detection of two outbursts of the Fanaroff-Riley I radio galaxy NGC 1275 that were detected by LHAASO-WCDA between November 2022 and January 2023 with statistical significance of 5.2 σ and 8.3 σ. The observed spectral energy distribution in the range from 500 GeV to 3 TeV is fitted by a power-law with a best-fit spectral index of α = −3.37 ± 0.52 and −3.35 ± 0.29, respectively. The outburst flux above 0.5 TeV was ($4.55\pm 4.21)\times ~10^{-11}~\rm cm^{-2}~s^{-1}$ and ($3.45\pm 1.78)\times ~10^{-11}~\rm cm^{-2}~s^{-1}$, corresponding to 60%, 45% of Crab Nebula flux. Variation analysis reveals the variability time-scale of days at the TeV energy band. A simple test by one-zone synchrotron self-Compton model reproduces the data in the gamma-ray band well.