Discovery Of The Ultrahigh-Energy Gamma-Ray Source Lhaaso J2108+5157

Zhen Cao,F. Aharonian,Q. An, Axikegu,L. X. Bai,Y. X. Bai,Y. W. Bao,D. Bastieri,X. J. Bi,Y. J. Bi,H. Cai,J. T. Cai,Zhe Cao,J. Chang,J. F. Chang,B. M. Chen,E. S. Chen,J. Chen,Liang Chen,Long Chen,M. J. Chen,M. L. Chen,Q. H. Chen,S. H. Chen,S. Z. Chen,T. L. Chen,X. L. Chen,Y. Chen,N. Cheng,Y. D. Cheng,S. W. Cui,X. H. Cui,Y. D. Cui, B. D. Ettore Piazzoli,B. Z. Dai,H. L. Dai,Z. G. Dai, Dan-Zeng Dan-Zeng-Luo-Bu,D. Della Volpe,X. J. Dong,K. K. Duan,J. H. Fan,Y. Z. Fan,Z. X. Fan,J. Fang,K. Fang,C. F. Feng,L. Feng,S. H. Feng,Y. L. Feng,B. Gao,C. D. Gao,L. Q. Gao,Q. Gao,W. Gao,M. M. Ge,L. S. Geng,G. H. Gong,Q. B. Gou,M. H. Gu,F. L. Guo,J. G. Guo,X. L. Guo,Y. Q. Guo,Y. Y. Guo,Y. A. Han,H. H. He,H. N. He,J. C. He,S. L. He,X. B. He,Y. He,M. Heller,Y. K. Hor,C. Hou,H. B. Hu,S. Hu,S. C. Hu,X. J. Hu,D. H. Huang,Q. L. Huang,W. H. Huang,X. T. Huang,X. Y. Huang,Z. C. Huang,F. Ji,X. L. Ji,H. Y. Jia,K. Jiang,Z. J. Jiang,C. Jin,T. Ke,D. Kuleshov,K. Levochkin,B. B. Li,Cheng Li,Cong Li,F. Li,H. B. Li,H. C. Li,H. Y. Li,J. Li,K. Li,W. L. Li,X. R. Li,Xin Li,Y. 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. S. Liu,J. Y. Liu,M. Y. Liu,R. Y. Liu,S. M. Liu,W. Liu,Y. Liu,Y. N. Liu,Z. X. Liu,W. J. Long,R. Lu,H. K. Lv,B. Q. Ma,L. L. Ma,X. H. Ma,J. R. Mao,A. Masood,Z. Min,W. Mitthumsiri,T. Montaruli,Y. C. Nan,B. Y. Pang,P. Pattarakijwanich,Z. Y. Pei,M. Y. Qi,Y. Q. Qi,B. Q. Qiao,J. J. Qin,D. Ruffolo,V Rulev,A. Saiz,L. Shao,O. Shchegolev,X. D. Sheng,J. Y. Shi,H. C. Song,Yu Stenkin,V Stepanov,Y. Su,Q. N. Sun,X. N. Sun,Z. B. Sun,P. H. T. Tam,Z. B. Tang,W. W. Tian,B. D. Wang,C. Wang,H. Wang,H. G. Wang,J. C. Wang,J. S. Wang,L. P. Wang,L. Y. Wang,R. N. Wang,W. Wang,X. G. Wang,X. J. Wang,X. Y. Wang,Y. Wang,Y. D. Wang,Y. J. Wang,Y. P. 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,W. X. Wu,X. F. Wu,S. Q. Xi,J. Xia,J. J. Xia,G. M. Xiang,D. X. Xiao,G. Xiao,H. B. Xiao,G. G. Xin,Y. L. Xin,Y. Xing,D. L. Xu,R. X. Xu,L. Xue,D. H. Yan,J. Z. Yan,C. W. Yang,F. F. 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. D. Zeng,T. X. Zeng,W. Zeng,Z. K. Zeng,M. Zha,X. X. Zhai,B. B. Zhang,H. M. Zhang,H. Y. Zhang,J. L. Zhang,J. W. Zhang,L. X. Zhang,Li Zhang,Lu Zhang,P. F. Zhang,P. P. Zhang,R. Zhang,S. R. Zhang,S. S. Zhang,X. Zhang,X. P. Zhang,Y. F. Zhang,Y. L. Zhang,Yi Zhang,Yong Zhang,B. Zhao,J. Zhao,L. Zhao,L. Z. Zhao,S. P. Zhao,F. Zheng,Y. Zheng,B. Zhou,H. Zhou,J. N. Zhou,P. Zhou,R. Zhou,X. X. Zhou,C. G. Zhu,F. R. Zhu,H. Zhu,K. J. Zhu,X. Zuo

The Astrophysical Journal Letters（2021）

Cited 26|Views8

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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 9.5 sigma and 8.5 sigma, 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 +/- 0.18(stat). 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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Key words

Gamma-ray astronomy, Gamma-ray sources, Gamma-ray observatories

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