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arXiv · 2410.15353

Detection of very high-energy gamma-ray emission from the radio galaxy M87 with LHAASO

Zhen Cao·F. Aharonian·Axikegu·Y. X. Bai·Y. W. Bao·D. Bastieri·X. J. Bi·Y. J. Bi·W. Bian·A. V. Bukevich·Q. Cao·W. Y. Cao·Zhe Cao·J. Chang·J. F. Chang·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. Chen·N. Cheng·Y. D. Cheng·M. C. Chu·M. Y. Cui·S. W. Cui·X. H. Cui·Y. D. Cui·B. Z. Dai·H. L. Dai·Z. G. Dai·Danzengluobu·X. Q. Dong·K. K. Duan·J. H. Fan·Y. Z. Fan·J. Fang·J. H. Fang·K. Fang·C. F. Feng·H. Feng·L. Feng·S. H. Feng·X. T. Feng·Y. Feng·Y. L. Feng·S. Gabici·B. Gao·C. D. Gao·Q. Gao·W. Gao·W. K. Gao·M. M. Ge·T. T. Ge·L. S. Geng·G. Giacinti·G. H. Gong·Q. B. Gou·M. H. Gu·F. L. Guo·J. Guo·X. L. Guo·Y. Q. Guo·Y. Y. Guo·Y. A. Han·O. A. Hannuksela·M. Hasan·H. H. He·H. N. He·J. Y. He·Y. He·Y. K. Hor·B. W. Hou·C. Hou·X. Hou·H. B. Hu·Q. Hu·S. C. Hu·C. Huang·D. H. Huang·T. Q. Huang·W. J. Huang·X. T. Huang·X. Y. Huang·Y. Huang·Y. Y. Huang·X. L. Ji·H. Y. Jia·K. Jia·H. B. Jiang·K. Jiang·X. W. Jiang
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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 Large High Altitude Air Shower Observatory (LHAASO). M87 has been detected by LHAASO with a statistical significance $\sim 9σ$. The observed energy spectrum extends to 20 TeV, with a possible hardening at $\sim 20$ 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 (EBL) intensity is obtained. A strong VHE flare lasting eight days, with the rise time of $τ_{r}^{\rm rise} = 1.05\pm0.49$~days and decay time of $τ_{d}^{\rm decay} = 2.17\pm0.58$~days, was found in early 2022. A possible GeV flare is seen also in the Fermi-LAT data during the VHE flare period. The variability time as short as one day seen in the LHAASO data suggests a compact emission region with a size of $\sim 3\times 10^{15}δ\, {\rm cm}$ ($δ$ 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 $\sim 1\%$ for VHE flares with a flux above $ 10^{-11}{\rm~erg~cm^{-2}~s^{-1}}$.

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Zhen Cao, F. Aharonian, Axikegu, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, Q. Cao, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, 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. Chen, N. Cheng, Y. D. Cheng, M. C. Chu, M. Y. Cui, S. W. Cui, X. H. Cui, Y. D. Cui, B. Z. Dai, H. L. Dai, Z. G. Dai, Danzengluobu, X. Q. Dong, K. K. Duan, J. H. Fan, Y. Z. Fan, J. Fang, J. H. Fang, K. Fang, C. F. Feng, H. Feng, L. Feng, S. H. Feng, X. T. Feng, Y. Feng, Y. L. Feng, S. Gabici, B. Gao, C. D. Gao, Q. Gao, W. Gao, W. K. Gao, M. M. Ge, T. T. Ge, L. S. Geng, G. Giacinti, G. H. Gong, Q. B. Gou, M. H. Gu, F. L. Guo, J. Guo, X. L. Guo, Y. Q. Guo, Y. Y. Guo, Y. A. Han, O. A. Hannuksela, M. Hasan, H. H. He, H. N. He, J. Y. He, Y. He, Y. K. Hor, B. W. Hou, C. Hou, X. Hou, H. B. Hu, Q. Hu, S. C. Hu, C. Huang, D. H. Huang, T. Q. Huang, W. J. Huang, X. T. Huang, X. Y. Huang, Y. Huang, Y. Y. Huang, X. L. Ji, H. Y. Jia, K. Jia, H. B. Jiang, K. Jiang, X. W. Jiang. 2025-12-26. Detection of very high-energy gamma-ray emission from the radio galaxy M87 with LHAASO. https://doi.org/10.3847/2041-8213%2Fad8921

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