LHAASO-WCDA Detection of TeV Flaring Activity from the Blazar 1ES 1959+650

ATel #18072; Guangman Xiang (IHEP), Min Zha (IHEP), Zhiguo Yao (IHEP), Jianeng Zhou (SHAO) and Yi Xing (SHAO) report on behalf of the LHAASO Collaboration
on 22 Sep 2026; 15:29 UT
Credential Certification: Guangman Xiang (gmxiang@ihep.ac.cn)

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Recent observation with the SST-1M has unveiled bright gamma-ray flaring activity from the blazar 1ES 1959+650 (ATel #18065).

Corresponding very-high-energy (VHE) flaring emission from this source has been independently detected by the real-time alert system of LHAASO-WCDA. During the 32-day time window spanning 2026-08-21 to 2026-09-21, preliminary data analysis reveals a significant VHE gamma-ray excess with a test statistic (TS) of 81.5, equivalent to a statistical significance of ∼ 7.7 σ. The preliminary intrinsic energy spectrum of the flare, covering the energy range of 0.6 – 7 TeV, is well fitted by a simple power-law model. The observed photon index is Γ = 3.24 ± 0.14(statistical uncertainties only). The corresponding integral flux above 1 TeV is approximately 0.5 times the Crab Nebula flux.

Given the current high flux state of 1ES 1959+650 across the gamma-ray, VHE, and optical bands, we strongly encourage multi-wavelength follow-up observations to characterize the full flaring evolution and physical properties of the source.

LHAASO is a multi-purpose Extensive Air Shower (EAS) array designed to detect air showers induced by gamma rays and cosmic rays from sub-TeV energies to above 1 PeV.