Reverberation Mapping of Changing-look Active Galactic Nucleus NGC 3516

Abstract

The changes of broad emission lines should be a crucial issue to understanding the physical properties of changing-look active galactic nucleus (CL-AGN). Here, we present the results of an intensive and homogeneous 6-month long reverberation mapping (RM) monitoring campaign during a low-activity state of the CL-AGN Seyfert galaxy NGC 3516. Photometric and spectroscopic monitoring was carried out during 2018--2019 with the Lijiang 2.4 m telescope. The sampling is 2 days in most nights, and the average sampling is $\sim$3 days. The rest frame time lags of H$\alpha$ and H$\beta$ are ${\tau }_{\mathrm{H}\alpha }=7.56_{-2.10}^{+4.42}$ days and ${\tau }_{\mathrm{H}\beta }=7.50_{-0.77}^{+2.05}$ days, respectively. From a RMS H$\beta$ line dispersion of ${\sigma }_{\mathrm{line}}=1713.3\pm 46.7$ $\mathrm{km}$ ${\mathrm{s}}^{-1}$ and a virial factor of $f_{\sigma }$ = 5.5, the central black hole mass of NGC 3516 is estimated to be $M_{\mathrm{BH}}=2.4_{-0.3}^{+0.7}\times 10^7{M}_{\odot }$, which is in agreement with previous estimates. The velocity-resolved delays show that the time lags increase towards negative velocity for both H$\alpha$ and H$\beta$. The velocity-resolved RM of H$\alpha$ is done for the first time. These RM results are consistent with other observations before the spectral type change, indicating a basically constant BLR structure during the changing-look process. The CL model of changes of accretion rate seems to be favored by long-term H$\beta$ variability and RM observations of NGC 3516.

25 pages, 6 figures, Accepted for publication in ApJ

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• Reverberation Mapping Measurements of Black Hole Masses and Broad-Line Region Kinematics in Mrk 817 and NGC 7469
• Reverberation Mapping of Two Luminous Quasars: the Broad-line Region Structure and Black Hole Mass