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ABSTRACT We have measured the wavelength-dependent lags between the X-ray, ultraviolet, and optical bands in the high-accretion rate ($$L/L_{\rm Edd}\approx 40{{\ \rm per\ cent}}$$) active galactic nucleus (AGN) Mrk 110 during two intensive monitoring campaigns in February and September 2019. After including the 2017 data published by Vincentelli et al., we divided the observations into three intervals with different X-ray luminosities. The first interval has the lowest X-ray luminosity and did not exhibit the U-band excess positive lag, or the X-ray excess negative lag that is seen in most AGNs. However, these excess lags are seen in the two subsequent intervals of higher X-ray luminosity. Although the data are limited, the excess lags appear to scale with X-ray luminosity. Our modelling shows that lags expected from reprocessing of X-rays by the accretion disc vary hardly at all with increasing luminosity. Therefore, as the U-band excess almost certainly arises from Balmer-continuum emission from the broad-line region (BLR), we attribute these lag changes to changes in the contribution from the BLR. The change is easily explained by the usual increase in the inner radius of the BLR with increasing ionizing luminosity. 

ABSTRACT Using a month-long X-ray light curve from RXTE/PCA and 1.5 month-long UV continuum light curves from IUE spectra in 1220–1970 Å, we performed a detailed time-lag study of the Seyfert 1 galaxy NGC 7469. Our cross-correlation analysis confirms previous results showing that the X-rays are delayed relative to the UV continuum at 1315 Å by 3.49 ± 0.22 d, which is possibly caused by either propagating fluctuation or variable Comptonization. However, if variations slower than 5 d are removed from the X-ray light curve, the UV variations then lag behind the X-ray variations by 0.37 ± 0.14 d, consistent with reprocessing of the X-rays by a surrounding accretion disc. A very similar reverberation delay is observed between Swift/XRT X-ray and Swift/UVOT UVW2, U light curves. Continuum light curves extracted from the Swift/GRISM spectra show delays with respect to X-rays consistent with reverberation. Separating the UV continuum variations faster and slower than 5 d, the slow variations at 1825 Å lag those at 1315 Å by 0.29 ± 0.06 d, while the fast variations are coincident (0.04 ± 0.12 d). The UV/optical continuum reverberation lag from IUE, Swift, and other optical telescopes at different wavelengths are consistent with the relationship: τ ∝ λ4/3, predicted for the standard accretion disc theory while the best-fitting X-ray delay from RXTE and Swift/XRT shows a negative X-ray offset of ∼0.38 d from the standard disc delay prediction. 

ABSTRACT We broadly explore the effects of systematic errors on reverberation mapping lag uncertainty estimates from javelin and the interpolated cross-correlation function (ICCF) method. We focus on simulated light curves from random realizations of the light curves of five intensively monitored AGNs. Both methods generally work well even in the presence of systematic errors, although javelin generally provides better error estimates. Poorly estimated light-curve uncertainties have less effect on the ICCF method because, unlike javelin , it does not explicitly assume Gaussian statistics. Neither method is sensitive to changes in the stochastic process driving the continuum or the transfer function relating the line light curve to the continuum. The only systematic error we considered that causes significant problems is if the line light curve is not a smoothed and shifted version of the continuum light curve but instead contains some additional sources of variability. 

ABSTRACT We present the first intensive continuum reverberation mapping study of the high accretion-rate Seyfert galaxy Mrk 110. The source was monitored almost daily for more than 200 d with the Swift X-ray and ultraviolet (UV)/optical telescopes, supported by ground-based observations from Las Cumbres Observatory, the Liverpool Telescope, and the Zowada Observatory, thus extending the wavelength coverage to 9100 Å. Mrk 110 was found to be significantly variable at all wavebands. Analysis of the intraband lags reveals two different behaviours, depending on the time-scale. On time-scales shorter than 10 d the lags, relative to the shortest UV waveband (∼1928 Å), increase with increasing wavelength up to a maximum of ∼2 d lag for the longest waveband (∼9100 Å), consistent with the expectation from disc reverberation. On longer time-scales, however, the g-band lags the Swift BAT hard X-rays by ∼10 d, with the z-band lagging the g-band by a similar amount, which cannot be explained in terms of simple reprocessing from the accretion disc. We interpret this result as an interplay between the emission from the accretion disc and diffuse continuum radiation from the broad-line region.