Detection of Very High-energy Gamma-Ray Emission from the Radio Galaxy M87 with LHAASO

/ Authors

Z. Cao, F. Aharonian, Axikegu, Y. Bai, Y. Bao, D. Bastieri, X. Bi, Y. Bi, W. Bian, A. V. Bukevich

and 285 more authors

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

/ Abstract

The nearby radio galaxy M87 is a very high-energy (VHE) gamma-ray emitter established by observations with ground-based gamma-ray detectors. Here we report the long-term monitoring of M87 from 2021 to 2024 with the Large High Altitude Air Shower Observatory (LHAASO). M87 has been detected by LHAASO with a statistical significance ∼ 9σ. The observed energy spectrum extends to 20 TeV, with a possible hardening at ∼20 TeV and then a clear softening at higher energies. Assuming that the intrinsic spectrum is described by a single power law up to 20 TeV, a tight upper bound on the extragalactic background light intensity is obtained. A strong VHE flare lasting 8 days, with a rise time of τrrise=1.05±0.49 days and decay time of τddecay=2.17±0.58 days, was found in early 2022. A possible GeV flare is seen also in Fermi Large Area Telescope data during the VHE flare period. The variability time as short as 1 day seen in the LHAASO data suggests a compact emission region with a size of ∼3 × 1015 δ cm (δ being the Doppler factor of the emitting region), corresponding to a few Schwarzschild radii of the central supermassive black hole in M87. The continuous monitoring of the source reveals a duty cycle of ∼1% for VHE flares with a flux above 10−11 erg cm−2 s−1.

Journal: The Astrophysical Journal Letters

DOI: 10.3847/2041-8213/ad8921