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Abstract Continuum reverberation mapping probes the size scale of the optical continuum-emitting region in active galactic nuclei (AGN). Through 3 yr of multiwavelength photometric monitoring in the optical with robotic observatories, we perform continuum reverberation mapping on Mrk 876. All wave bands show large-amplitude variability and are well correlated. Slow variations in the light curves broaden the cross-correlation function (CCF) significantly, requiring detrending in order to robustly recover interband lags. We measure consistent interband lags using three techniques (CCF, JAVELIN, and PyROA), with a lag of around 13 days fromutoz. These lags are longer than the expected radius of 12 days for the self-gravitating radius of the disk. The lags increase with wavelength roughly followingλ^4/3, as would be expected from thin disk theory, but the lag normalization is approximately a factor of 3 longer than expected, as has also been observed in other AGN. The lag in theiband shows an excess that we attribute to variable Hαbroad-line emission. A flux–flux analysis shows a variable spectrum that followsf_ν∝λ^−1/3, as expected for a disk, and an excess in theiband that also points to strong variable Hαemission in that band. 

ABSTRACT We carried out photometric and spectroscopic observations of the well-studied broad-line radio galaxy 3C 120 with the Las Cumbres Observatory (LCO) global robotic telescope network from 2016 December to 2018 April as part of the LCO AGN Key Project on Reverberation Mapping of Accretion Flows. Here, we present both spectroscopic and photometric reverberation mapping results. We used the interpolated cross-correlation function to perform multiple-line lag measurements in 3C 120. We find the H γ, He ii λ4686, H β, and He i λ5876 lags of $$\tau _{\text{cen}} = 18.8_{-1.0}^{+1.3}$$, $$2.7_{-0.8}^{+0.7}$$, $$21.2_{-1.0}^{+1.6}$$, and $$16.9_{-1.1}^{+0.9}$$ d, respectively, relative to the V-band continuum. Using the measured lag and rms velocity width of the H β emission line, we determine the mass of the black hole for 3C 120 to be $$M=(6.3^{+0.5}_{-0.3})\times 10^7\, (f/5.5)$$ M⊙. Our black hole mass measurement is consistent with similar previous studies on 3C 120, but with small uncertainties. In addition, velocity-resolved lags in 3C 120 show a symmetric pattern across the H β line, 25 d at line centre decreasing to 17 d in the line wings at ±4000 km s−1. We also investigate the inter-band continuum lags in 3C 120 and find that they are generally consistent with τ ∝ λ4/3 as predicted from a geometrically thin, optically thick accretion disc. From the continuum lags, we measure the best-fitting value τ0 = 3.5 ± 0.2 d at $$\lambda _{\rm 0} = 5477\, \mathring{\rm A}$$. It implies a disc size a factor of 1.6 times larger than prediction from the standard disc model with L/LEdd = 0.4. This is consistent with previous studies in which larger than expected disc sizes were measured. 

Abstract In this third paper of the series reporting on the reverberation mapping campaign of active galactic nuclei with asymmetric H β emission-line profiles, we present results for 15 Palomar–Green quasars using spectra obtained between the end of 2016–2021 May. This campaign combines long time spans with relatively high cadence. For eight objects, both the time lags obtained from the entire light curves and the measurements from individual observing seasons are provided. Reverberation mapping of nine of our targets has been attempted for the first time, while the results for six others can be compared with previous campaigns. We measure the H β time lags over periods of years and estimate their black hole masses. The long duration of the campaign enables us to investigate their broad-line region (BLR) geometry and kinematics for different years by using velocity-resolved lags, which demonstrate signatures of diverse BLR geometry and kinematics. The BLR geometry and kinematics of individual objects are discussed. In this sample, the BLR kinematics of Keplerian/virialized motion and inflow is more common than that of outflow.