LHAASO-WCDA observed a ∼ 5 days TeV-delayed flaring event in blazar 1ES 1959+650

@misc{cao2026lhaasowcda,
  title = {{LHAASO-WCDA observed a $\sim$ 5 days TeV-delayed flaring event in blazar 1ES 1959+650}},
  author = {Zhen Cao and F Aharonian and Y.X Bai and Y.W Bao and D Bastieri and X.J Bi and Y.J Bi and W Bian and J Blunier and A.V Bukevich and C.M Cai and W.Y Cao and Zhe Cao and J Chang and J.F Chang and E.S Chen and G.H Chen and H.K Chen and L.F Chen and Liang Chen and Long Chen and M.J Chen and M.L Chen and Q.H Chen and S Chen and S.H Chen and S.Z Chen and T.L Chen and X.B Chen and X.J Chen and X.P Chen and Y Chen and N Cheng and Q.Y Cheng and Y.D Cheng and M.Y Cui and S.W Cui and X.H Cui and Y.D Cui and B.Z Dai and H.L Dai and L.X Dai and Z.G Dai and M Danzengluobu and Y.X Diao and A.J Dong and X.D Duan and J.H Fan and Y.Z Fan and J Fang and J.H Fang and K Fang and C.F Feng and H Feng and L Feng and S.H Feng and X.T Feng and Y Feng and Y.L Feng and S Gabici},
  howpublished = {HAL},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.02853},
  eprint = {2609.02853},
  archivePrefix = {arXiv},
  url = {https://hal.science/hal-05759195v1},
}

TY  - UNPB
TI  - LHAASO-WCDA observed a ∼ 5 days TeV-delayed flaring event in blazar 1ES 1959+650
AU  - Zhen Cao
AU  - F Aharonian
AU  - Y.X Bai
AU  - Y.W Bao
AU  - D Bastieri
AU  - X.J Bi
AU  - Y.J Bi
AU  - W Bian
AU  - J Blunier
AU  - A.V Bukevich
AU  - C.M Cai
AU  - W.Y Cao
AU  - Zhe Cao
AU  - J Chang
AU  - J.F Chang
AU  - E.S Chen
AU  - G.H Chen
AU  - H.K Chen
AU  - L.F Chen
AU  - Liang Chen
AU  - Long Chen
AU  - M.J Chen
AU  - M.L Chen
AU  - Q.H Chen
AU  - S Chen
AU  - S.H Chen
AU  - S.Z Chen
AU  - T.L Chen
AU  - X.B Chen
AU  - X.J Chen
AU  - X.P Chen
AU  - Y Chen
AU  - N Cheng
AU  - Q.Y Cheng
AU  - Y.D Cheng
AU  - M.Y Cui
AU  - S.W Cui
AU  - X.H Cui
AU  - Y.D Cui
AU  - B.Z Dai
AU  - H.L Dai
AU  - L.X Dai
AU  - Z.G Dai
AU  - M Danzengluobu
AU  - Y.X Diao
AU  - A.J Dong
AU  - X.D Duan
AU  - J.H Fan
AU  - Y.Z Fan
AU  - J Fang
AU  - J.H Fang
AU  - K Fang
AU  - C.F Feng
AU  - H Feng
AU  - L Feng
AU  - S.H Feng
AU  - X.T Feng
AU  - Y Feng
AU  - Y.L Feng
AU  - S Gabici
PY  - 2026
DA  - 2026/09/02
PB  - HAL
DO  - 10.48550/arxiv.2609.02853
UR  - https://hal.science/hal-05759195v1
AB  - We report a day-scale hard lag between GeV and TeV γ-ray emission from the HBL 1ES~1959+650 in early 2024. Since the LHAASO-WCDA real-time monitoring system began operation in late 2023, multiple TeV flares from this source have been triggered, including the 1st trigger flare on 2024 February 9. A Bayesian-block analysis of the WCDA light curve identifies three TeV flares in 2024. For the second triggered flare, a discrete cross-correlation analysis reveals a >3 σ correlation (relative to uncorrelated red-noise simulations) at a time delay of Δt = 5.0_−2.1^+2.1 days, with the TeV emission lagging the GeV. Time-resolved spectroscopy shows that this flare has the softest TeV spectrum among these flares (intrinsic spectral index Γ=3.16±0.18), while the 1st trigger flare is harder (Γ=2.48±0.21). The observed five-day hard lag is difficult to reconcile with a purely cooling-driven temporal ordering and is consistent with scenarios in which particle energization and/or transport may contribute to the evolution. However, the current data do not uniquely identify the underlying mechanism.
ER  -