Discovery of the Ultrahigh-energy Gamma-Ray Source LHAASO J2108+5157

Z Cao ,M Y Qi,Liang Chen,S L He,A Masood,J S Liu,J C Wang,H Zhou,Y Chen,Q An,S H Feng,K Levochkin,Q H Chen,T Montaruli,R N Wang,Y F Zhang,X T Huang,Y D Wang,D Kuleshov,L P Wang,Yi Zhang,J Liu,X H You,P P Zhang,S J Lin,C Liu,L Q Yin,C Wang,B Liu,J T Cai,B D’Ettorre Piazzoli,H Y Li,Z G Yao,J F Chang,M Zha,F Zheng,J J Wei,X J Wang,W J Long,H G Wang,S C Hu,S B Yang,B M Chen,Y H Yu,Yu V Stenkin,J G Guo,S Z Chen,H Liu,X G Wang,L Xue,H Y Zhang,Y K Hor,S R Zhang,M M Ge,C G Zhu,D Bastieri,W Wang,Q N Sun,R X Xu,J Xia,D Liu,Y Q Qi,M J Chen,Zheng Wang,S W Cui,Yong Zhang,F R Zhu,V Stepanov,S H Chen,J H Fan,D X Xiao,Z J Jiang,Y C Nan,Lu Zhang,D Ruffolo,P Pattarakijwanich,X J Bi,X X Zhou,Long Chen,G G Xin,H C Song,Cheng Li,Axikegu Axikegu,W Mitthumsiri,Y Li,Zhuo Li,Y Y Guo,Zhe Li,H B Li,Q B Gou,M L Chen,X R Li,Dan-Zeng Dan-Zeng-Luo-Bu,H L Dai,A Sáiz,Y He,X D Sheng,Y H Yao,L S Geng,E S Chen,W Zeng,Y J Bi,B Z Dai,Y Z Li,F Li,Cong Li,H B Xiao,G M Xiang,Z G Dai,J W Zhang,K Li,Y P Wang,S P Zhao,J Zhao,X P Zhang,X L Chen,M Heller,P H T Tam,Z C Huang,Xin Li,Y Q Guo,X X Zhai,B Y Pang,V Rulev,M H Gu,Y A Han,Y Zheng,F Aharonian,Y L Zhang,J Chen,Z X Wang,D L Xu,Y M Ye,X L Ji,Zhe Cao,J Y Liu,L X Zhang,Y J Wang,Zhen Wang,Z K Zeng,J L Zhang,D Della Volpe,P F Zhang,T L Chen,Z X Liu,H C Li,W L Li,L Y Wang,B D Wang,B B Li,Y J Wei,Y Liu,C Y Wu,H Cai,J L Liu,H D Liu,J S Wang,H H He,M Y Liu,W X Wu,H Y Jia,L Shao,Z Y You,Z Y Pei,S S Zhang,K J Zhu,Y L Feng,Y N Liu,R Zhang,J He ,Jianeng Zhou ,Jiajun Qin ,Kun Fang ,Hai-Ming Zhang ,Bin Zhou ,Kai-Kai Duan ,Zhang‐Hua Sun ,Guanghua Gong ,Li Feng ,Fang Yang ,Liang Gao ,Chaowen Yang ,Chao Hou ,Yang Su ,Shao-Qiang Xi ,X Dong ,B Q ,Yi Xing ,Z Tang ,Zhao Liu ,X H ,Ping Zhou ,Lixin Bai ,Ning Cheng ,R Yang ,Bing-Qiang Qiao ,C Feng ,Yudong Cui ,Xiaolei Guo ,Yun-Feng Liang ,Siming Liu ,Chengyong Gao ,Hongkui Lv ,Bing Zhao ,Min Yang ,Jian-Huan Yang ,Jian Li ,J Mao ,D Huang ,Rui Lü ,Q Huang ,Lili Yang ,Hongbo Hu ,Na Yin ,Zhongxiang Wang ,Xinbo He ,Xiaohong Cui ,Xiang-Yu Wang ,G C Xiao ,Y Xin ,John Shi ,Fulai Guo ,Wenhao Huang ,Tian Wu ,Fang-Wu Lu ,Xiaoyuan Huang ,Yiwei Bao ,Fan Zhou ,Da-Ming Wei ,T Wen ,Wei Liu ,Ke Tang ,Xiao Zhang ,Hong Wu ,Fei Ji ,Yaodong Cheng ,Tingxuan Zeng ,L L ,Wei Gao ,Hong Guang Wang ,Bo Gao ,Houdun Zeng ,En‐Wei Liang ,Chao Jin ,Yang Wang ,Yi‐Zhong Fan ,Jun Yan ,Qi Gao ,X Hu ,O Shchegolev ,San Wu ,Wei Wang ,Rong Zhou ,Ruo-Yu Liu ,Bin-Bin Zhang ,Dahai Yan ,Y Bai ,Xue-Feng Wu ,Jun Fang ,Hao-Ning He ,Hui Zhu ,Xiao-Na Sun ,Qiang Yuan ,Xin Zuo

doi:10.3847/2041-8213/ac2579

Abstract

Abstract We report the discovery of an ultrahigh-energy (UHE) gamma-ray source, LHAASO J2108+5157, by analyzing the LHAASO-KM2A data of 308.33 live days. A significant excess of gamma ray–induced showers is observed in both energy bands of 25−100 and >100 TeV with 9.5σ and 8.5σ, respectively. This source is not significantly favored as an extended source with an angular extension smaller than the point-spread function of KM2A. The measured energy spectrum from 20 to 200 TeV can be approximately described by a power-law function with an index of −2.83 ± 0.18stat. A harder spectrum is demanded at lower energies considering the flux upper limit set by Fermi-LAT observations. The position of the gamma-ray emission is correlated with a giant molecular cloud, which favors a hadronic origin. No obvious counterparts have been found, and deeper multiwavelength observations will help to cast new light on this intriguing UHE source.

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