The reverberation mapping uses time resolution of line strengths as a proxy for spatial resolution.
https://arxiv.org/abs/2208.02966
Changing-look active galactic nucleus NGC 4151, which has attracted a lot of attention, is undergoing the
second dramatic outburst stage in its evolutionary history. To investigate the geometry and kinematics of the
broad-line region (BLR), and measure the mass of supermassive black hole in NGC 4151, we perform a seven-
month photometric and spectroscopic monitoring program in 2020–2021, using the 2.4 m telescope at Lijiang
Observatory. We successfully measure the time lags of the responses from broad Hα, Hβ, Hγ, He I, and He II
emission lines to continuum variation, which are 7.63+1.85−2.62, 6.21+1.41−1.13, 5.67+1.65−1.94,
1.59+0.86−1.11, and 0.46+1.22−1.06days, respectively, following radial stratification. The ratios of time lags
among these lines are 1.23 : 1.00 :0.91 : 0.26 : 0.07. We find that the continuum lag between the ultraviolet
and optical bands can significantly affect the lag measurements of He I and He II. Virial and infalling gas motions
coexist in this campaign, which is different from previous results, implying the evolutionary kinematics of BLR.
Based on our measurements and previous ones in the literature, we confirm that the BLR of NGC 4151 is basically
virialized. Finally, we compute the black hole mass through multiplel ines, and themeasurement from Hβ to be
3.94+0.90×107M−0.72 ⊙ which is consistent with previous results. The corresponding accretion rate is
0.02+0.01−1.11 LEdd c^−2, implying a sub-Eddington accretor.
