Review of extragalactic sources detected by LHAASO-WCDA

This talk presents a comprehensive study of Mrk 421 using three years of observations from the LHAASO-WCDA detector, spanning from March 2021 to March 2024 in the energy range of 0.4–13 TeV. Benefiting from the detector’s continuous and unbiased monitoring capabilities, we construct a continuous light curve sampled at a daily cadence and identify 23 very-high-energy (VHE) flaring episodes using the Bayesian Blocks algorithm. The durations of these flares vary widely, ranging from sub-day timescales to several weeks, with the most intense reaching up to 3.3 Crab Unit. Spectral analysis shows that all flares can be well described by a power-law model, with the photon index exhibiting a “harder-when-brighter” trend. The flaring duty cycle is calculated to be approximately 14.6%, depending on the flux threshold. In addition, long-term averaged spectra are extracted for each year, and spectral fits with EBL absorption correction indicate significant inter-annual variability in both flux normalization and cutoff energy. These results highlight the capability of LHAASO for long-term TeV-band blazar monitoring and provide valuable insight into the high-energy emission behavior of Mrk 421.