long-term observation of the blazars Mrk 421by LHAASO

Key extra-galactic sources of VHE gamma rays include blazars, gamma-ray bursts (GRBs), and other interesting transients phenomena. The studies on these targets provides critical insights into astrophysical phenomena, including black hole accretion, particle acceleration, and explosion dynamics. The Large High Altitude Air Shower Observatory (LHAASO), located in China, is a multi-purpose facility designed to detect cosmic rays and gamma rays in the energy range from a few hundred GeV to a few hundred PeV. As one of three sub-arrays comprising LHAASO, the Water Cherenkov Detector Array (WCDA), with its wide field of view, high duty cycle, and high sensitivity, provides an ideal platform for capturing these flaring phenomena, contributing to a deeper understanding of such astrophysical phenomena. In this talk, we will review the extragalactic sources detected by LHAASO-WCDA, along with a preliminary catalog of these sources. Additionally, we will discuss transient event analysis, including the monitoring framework, analysis pipeline, and preliminary results