Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. 6: Variability of NGC 3783 from ground-based data

Abstract

The Seyfert 1 galaxy NGC 3783 was intensely monitored in several bands between 1991 December and 1992 August. This paper presents the results from the ground-based observations in the optical and near-IR bands, which complement the data-set formed by the International Ultraviolet Explorer (IUE) spectra, discussed elsewhere. Spectroscopic and photometric data from several observatories were combined in order to obtain well sampled light curves of the continuum and of Hβ. During the campaign the source underwent significant variability. The light curves of the optical continuum and of Hβ display strong similarities with those obtained with the IUE. The near-IR flux did not vary significantly except for a slight increase at the end of the campaign.The cross correlation analysis shows that the variations of the optical continuum have a lag of 1 day or less with respect to those of the UV continuum, with an uncertainty of ≤ 4 days. The integrated flux of Hβ varies with a delay of about 8 days. These results confirm that (a) the continuum variations occur simultaneously or with a very small lag across the entire UV-optical range, as in the Seyfert galaxy NGC 5548; and (b) the emission lines of NGC 3783 respond to ionizing continuum variations with less delay than those of NGC 5548. As observed in NGC 5548, the lag of Hβ with respect to the continuum is greater than those of the high ionization lines.

The Mass of the Central Black Hole in the Seyfert Galaxy NGC 3783

“…The results of that work have been published by Reichert et al (1994), Stirpe et al (1994), and Alloin et al (1995). Compared to the consortium's earlier study of another Seyfert galaxy, NGC 5548 (see Clavel et al 1991;Peterson et al 1991;Dietrich et al 1993), the emission-line time lags were relatively uncertain, too poorly constrained in fact to reveal any possible virial relationship between line width and time lag.…”

“…The optical data analyzed here were retrieved from the AGN Watch Web site, 2 and details of the observations are described by Stirpe et al (1994). We have limited our investigation to the data gathered at the Cerro Tololo Inter-American Observatory (CTIO) 1.0 m telescope to ensure the most homogeneous data set possible for the cross-correlation analysis and for the construction of the mean and rms spectra.…”

A Test of the Formation Mechanism of the Broad Line Region in Active Galactic Nuclei

“…We use the time delay measurements of Hβ emission line summarized in Du et al (2015Du et al ( , 2016, which are compiled from the reverberation campaigns performed by different groups (Barth et al 2013, 2009b, 2014, Collier et al 1998, Dietrich et al 1993, 2015, Kaspi et al 2000, Pei et al 2014, Peterson et al 1991, 1992, 2002, 2014, Santos-Lleó et al 1997, 2001, Stirpe et al 1994, Wang et al 2014. The time delays represent the emissivity-weighted radii of the BLR in those RM objects.…”

Space Telescope and Optical Reverberation Mapping Project. V. Optical Spectroscopic Campaign and Emission-line Analysis for NGC 5548

“…This can significantly affect the measured broadline lag if the BLR has a characteristic radius on the order of light-days. The variable optical continuum has also been shown to have smoother features and smaller amplitudes than its UV counterpart (e.g., Peterson et al 1991;Dietrich et al 1993Dietrich et al , 1998Stirpe et al 1994;Santos-Lleó et al 1997;Shappee et al 2014;Fausnaugh et al 2016). These differences between the UV and optical continua suggest that the optical continuum is not fully interchangeable with the ionizing source for determining reverberation lags.…”