Discovery of a New Gamma-Ray Source, LHAASO J0341+5258, with Emission up to 200 TeV
Z. Cao, F. Aharonian, Qi An, Axikegu, Lixin Bai, Y. X. Bai, Y. W. Bao, D. Bastieri, Xiao-Jun Bi, Y. J. Bi, H. Cai, J. T. Cai, Zhe Cao, J. F. Chang, J. F. Chang, B. M. Chen, E. S. Chen, J. Chen, Liang Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Qi-Hui Chen, S. H. Chen, S. Z. Chen, T. L. Chen, X. L. Chen, Yang Chen, Ning Cheng, Yaodong Cheng, S. W. Cui, X. H. Cui, Y. D. Cui, B. D′Ettorre Piazzoli, B. Z. Dai, H. L. Dai, Zi-Gao Dai, Danzengluobu Danzengluobu, D. della Volpe, X. Dong, K. K. Duan, J. H. Fan, Y. Z. Fan, Z. X. Fan, J. Fang, Kun Fang, Chunsheng Feng, Li Feng, S. H. Feng, Y. L. Feng, B. S. Gao, C. D. Gao, L. Q. Gao, Qing Gao, W. X. Gao, M. M. Ge, Li‐Sheng Geng, G. Gong, Q. B. Gou, M. H. Gu, Fulai Guo, J. G. Guo, Xueling Guo, Yi-Qing Guo, Y. Y. Guo, Y. A. Han, H. H. He, Hao-Ning He, J. C. He, S. L. He, Xinyu He, Y. He, Matthieu Heller, Y. K. Hor, C. Hou, H. B. Hu, S. Hu, S. C. Hu, X. Hu, D. H. Huang, Q. Huang, W. H. Huang, X. T. Huang, X. Y. Huang, Zhongjie Huang, Fei Ji, X. L. Ji, H. Y. Jia, K. Jiang, Z. J. Jiang, Chichuan Jin, T. Ke, D. Kuleshov, K. Levochkin, B. B. Li, Cheng Li, Cong Li, Fenghe Li, Hao Li
Abstract
Abstract We report the discovery of a new unidentified extended γ -ray source in the Galactic plane named LHAASO J0341+5258 with a pretrial significance of 8.2 standard deviations above 25 TeV. The best-fit position is R.A. = 55.°34 ± 0.°11 and decl. = 52.°97 ± 0.°07. The angular size of LHAASO J0341+5258 is 0.°29 ± 0.°06 stat ± 0.°02 sys . The flux above 25 TeV is about 20% of the flux of the Crab Nebula. Although a power-law fit of the spectrum from 10 to 200 TeV with the photon index α = 2.98 ± 0.19 stat ± 0.02 sys is not excluded, the LHAASO data together with the flux upper limit at 10 GeV set by the Fermi-LAT observation, indicate a noticeable steepening of an initially hard power-law spectrum with a cutoff at ≈50 TeV. We briefly discuss the origin of ultra-high-energy gamma rays. The lack of an energetic pulsar and a young supernova remnant inside or in the vicinity of LHAASO J0341+5258 challenge, but do not exclude, both the leptonic and hadronic scenarios of gamma-ray production.