Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XIV. Intensive Optical Spectrophotometric Observations of NGC 7469

We present results of an intensive 2 month campaign of ground-based spectrophotometric monitoring of the Seyfert 1 galaxy NGC 7469, with a temporal resolution [approximately less than]1 day. The broad Hα and Hβ emission lines respond to ~35% ultraviolet continuum variations with an amplitude of ~10% and time delays of 5.6±1.3 days and 5.4±0.8 days, respectively. We interpret this as evidence of variable Balmer line gas ~5-6 light days from the central source in this object, widely believed to be a supermassive black hole. The virial mass of the central source implied by line widths and time delays is ~106-107 M◉ Concomitantly, we find evidence for wavelength-dependent continuum time delays : optical continuum variations lag those at 1315 Å by 1.0±0.3 days at 4865 Å to 1.5±0.7 days at 6962 Å. . This suggests a stratified continuum reprocessing region extending several light days from the central source, possibly an accretion disk

MULTIWAVELENGTH MONITORING OF THE NARROW-LINE SEYFERT 1 GALAXY ARAKELIAN 564. III. OPTICAL OBSERVATIONS AND THE OPTICAL--UV--X-RAY CONNECTION

We present the results of a 2 yr long optical monitoring program of the narrow-line Seyfert 1 galaxy Ark 564. The majority of this monitoring project was also covered by X-ray observations (RXT E), and for a period of ~50 days, we observed the galaxy in UV (HST) and X-rays (RXTE and ASCA) simultaneously with the ground-based observations. Rapid and large-amplitude variations seen in the X-ray band, on a daily and hourly timescale, were not detected at optical and UV wavelengths, which in turn exhibited much lower variability either on short (1 day) or long (several months) timescales. The only significant optical variations can be described as two 2È4 day events with ~10% flux variations. We detect no significant optical line variations and thus cannot infer a reverberation size for the broad-line region. Similarly, the large X-ray variations seem to vanish when the light curve is smoothed over a period of 30 days. The UV continuum follows the X-rays with a lag of ~0.4 days, and the optical band lags the UV band by ~2 days. No signiÐcant correlation was found between the entire X-ray data set and the optical band. Focusing on a 20 day interval around the strongest optical event we detect a significant X-ray--optical correlation with similar events seen in the UV and X-rays. Our data are consistent with reprocessing models on the grounds of the energy emitted in this single event. However, several large X-ray flares produced no corresponding optical emission

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. VII. Variability of the optical spectrum of NGC 5548 over 4 years

We report on the results of a continuation of a large monitoring program of optical spectroscopy of the Seyfert 1 galaxy NGC 5548. The new observations presented here were obtained between 1990 December and 1992 October, and extend the existing database to nearly 1400 days, dating back to 1988 December. The continuum variations are generally smooth and well-resolved, except during the third year of this 4 year project, when the variations were apparently more rapid and of lower amplitude than observed at other times. The broad Hβ emission line is found to vary in response to the continuum variations with a lag of about 18 days, but with some changes from year to year. The Hβ transfer functions for each of the 4 yr and for the entire 4 yr database are derived by using a maximum entropy method

Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XII. Ground-based Monitoring of 3C 390.3

Results of a ground-based optical monitoring campaign on 3C 390.3 in 1994-1995 are presented. The broadband fluxes (B, V , R, and I), the spectrophotometric optical continuum flux Fλ(5177 Å), integrated emission-line fluxes of Hα, Hβ, Hγ, He I λ5876, and He II λ4686 all show a nearly monotonic increase with episodes of milder short-term variations superposed. The amplitude of the continuum variations increases with decreasing wavelength (4400-9000 Å). The optical continuum variations follow the variations in the ultraviolet and X-ray with time delays, measured from the centroids of the crosscorrelation functions, typically around 5 days, but with uncertainties also typically around 5 days; zero time delay between the high-energy and low-energy continuum variations cannot be ruled out. The strong optical emission lines Hα, Hβ, Hγ, He I λ5876 respond to the high-energy continuum variations with time delays typically about 20 days, with uncertainties of about 8 days. There is some evidence that He II λ4686 responds somewhat more rapidly, with a time delay of around 10 days, but again, the uncertainties are quite large (~8 days). The mean and rms spectra of the Hα and Hβ line profiles provide indications for the existence of at least three distinct components located at ±4000 and 0 km s-1 relative to the line peak. The emission-line proÐle variations are largest near line center

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. VIII. An intensive HST, IUE, and ground-based study of NGC 5548

We present the data and initial results from a combined HST/IUE/ground-based spectroscopic monitoring campaign on the Seyfert I galaxy NGC 5548 that was undertaken in order to address questions that require both higher temporal resolution and higher signal-to-noise ratios than were obtained in our previous multiwavelength monitoring of this galaxy in 1988-1989. IUE spectra were obtained once every 2 days for a period of 74 days beginning on 1993 March 14. During the last 39 days of this campaign, spectroscopic observations were also made with the HST Faint Object Spectrograph (FOS) on a daily basis. Ground-based observations, consisting of 165 optical spectra and 77 photometric observations (both eco imaging and aperture photometry), are reported for the period 1992 October-1993 September, although many of the data are concentrated around the time of the satellite-based program. These data constitute a fifth year of intensive optical monitoring of this galaxy. In this contribution we describe the acquisition and reduction of ali of the satellite and ground-based data obtained in this program. We describe in detail various photometric problems with the FOS and explain how we identified and corrected for various anomalies. During the HST portion of the monitoring campaign, the 1350 Å continuum flux is found to have varied by nearly a factor of 2. In other wave bands, the continuum shows nearly identical behavior, except that the amplitude of variability is larger at shorter wavelengths, and the continuum light curves appear to show more short­ timescale variability at shorter wavelengths. The broad emission lines also vary in flux, with amplitudes that are slightly smaller than the UV continuum variations and with a small time delay relative to the UV continuum. On the basis of simple time-series analysis of the UV and optical continuum and emission-line light curves, we find (1) that the ultraviolet and optical continuum variations are virtually simultaneous, with any lag between the 1350 Å continuum and the 5100 Å continuum amounting to less than about 1 day; (2) that the variations in the highest ionization lines observed, He II λ1640 and N v λ1240, lag behind the continuum variations by somewhat less than 2 days; and (3) that the velocity field of the C IV-emitting region is not dominated by radial motion. The results on the C IV velocity field are pretiminary and quite uncertain, but there are some weak indications that the emission-line wings (|Δv|≥ 3000 km s-ˡ) respond to continuum variations slightly more rapidly than does the core. The optical observations show that the variations in the broad Hβ line flux follow the continuum variations with time lag of around 2 weeks, about twice the lag for Lyα and C IV, as in our previous monitoring campaign on this same galaxy. However, the lags measured for Lyα, C IV, and Hβ are each slightly smaller than previous determmations. We confirm two trends reported eartier, namely, (1) that the UV /optical continuum becomes "harder" as it gets brighter and (2) that the highest ionization emission lines have the shortest lags, thus indicating radial ionization stratification of a broad-line region that spans over an order of magnitude range in radius

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. VIII. An intensive HST, IUE, and ground-based study of NGC 5548

We present the data and initial results from a combined HST/IUE/ground-based spectroscopic monitoring campaign on the Seyfert I galaxy NGC 5548 that was undertaken in order to address questions that require both higher temporal resolution and higher signal-to-noise ratios than were obtained in our previous multiwavelength monitoring of this galaxy in 1988-1989. IUE spectra were obtained once every 2 days for a period of 74 days beginning on 1993 March 14. During the last 39 days of this campaign, spectroscopic observations were also made with the HST Faint Object Spectrograph (FOS) on a daily basis. Ground-based observations, consisting of 165 optical spectra and 77 photometric observations (both eco imaging and aperture photometry), are reported for the period 1992 October-1993 September, although many of the data are concentrated around the time of the satellite-based program. These data constitute a fifth year of intensive optical monitoring of this galaxy. In this contribution we describe the acquisition and reduction of ali of the satellite and ground-based data obtained in this program. We describe in detail various photometric problems with the FOS and explain how we identified and corrected for various anomalies. During the HST portion of the monitoring campaign, the 1350 Å continuum flux is found to have varied by nearly a factor of 2. In other wave bands, the continuum shows nearly identical behavior, except that the amplitude of variability is larger at shorter wavelengths, and the continuum light curves appear to show more short­ timescale variability at shorter wavelengths. The broad emission lines also vary in flux, with amplitudes that are slightly smaller than the UV continuum variations and with a small time delay relative to the UV continuum. On the basis of simple time-series analysis of the UV and optical continuum and emission-line light curves, we find (1) that the ultraviolet and optical continuum variations are virtually simultaneous, with any lag between the 1350 Å continuum and the 5100 Å continuum amounting to less than about 1 day; (2) that the variations in the highest ionization lines observed, He II λ1640 and N v λ1240, lag behind the continuum variations by somewhat less than 2 days; and (3) that the velocity field of the C IV-emitting region is not dominated by radial motion. The results on the C IV velocity field are pretiminary and quite uncertain, but there are some weak indications that the emission-line wings (|Δv|≥ 3000 km s-ˡ) respond to continuum variations slightly more rapidly than does the core. The optical observations show that the variations in the broad Hβ line flux follow the continuum variations with time lag of around 2 weeks, about twice the lag for Lyα and C IV, as in our previous monitoring campaign on this same galaxy. However, the lags measured for Lyα, C IV, and Hβ are each slightly smaller than previous determmations. We confirm two trends reported eartier, namely, (1) that the UV /optical continuum becomes "harder" as it gets brighter and (2) that the highest ionization emission lines have the shortest lags, thus indicating radial ionization stratification of a broad-line region that spans over an order of magnitude range in radius