2025ApJ...995..157X

We present the results of the 2023 spectroscopic reverberation mapping campaign for active galactic nuclei (AGNs) of NGC 5548, continuing our long-term monitoring program. Using the Lijiang 2.4 m telescope, we obtained 74 spectra with a median cadence of 1.9 days. Through detailed spectral decomposition, we measured the light curves of the optical continuum at 5100 Å and the broad He II, He I, Hγ, and Hβ emission lines. The time lags of these lines relative to the continuum are measured as $1.{3}_{-0.6}^{+1.6}$, $2.{3}_{-2.1}^{+1.5}$, $10.{0}_{-1.8}^{+2.0}$, and $15.{6}_{-2.9}^{+2.6}$ days (rest frame), respectively. Velocity-resolved lag profiles for Hγ and Hβ were constructed. Combined with data from previous seasons (2015-2021), we found the following: the radial ionization stratification of the broad-line region (BLR) is stable; the average virial mass of the supermassive black hole in NGC 5548 is (2.6 ± 1.1) × 10⁸M_⊙, consistent with the M_BH-σ_* relation; broad He II line exhibits the largest responsivity, followed by broad He I (or Hγ) and Hβ lines; and the BLR kinematics show significant temporal evolution, transitioning from virialized motions to signatures of inflow and outflow. Furthermore, an analysis of 35 yr of historical data confirms a 3.5 yr time lag between variations in the optical luminosity and the BLR radius, potentially implicating the role of radiation pressure or dynamical structure changes in the inner accretion disk. Long-term campaign demonstrates that the BLR in NGC 5548 is a robust yet dynamically evolving entity, providing crucial insights into AGN structure and accretion physics.