A. I. Shapovalova

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 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 A by 1.0 ± 0.3 days at 4865 A to 1.5 ± 0.7 days at 6962 A. This suggests a stratified continuum reprocessing region extending several light days from the central source, possibly an accretion disk.

Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XVI. A 13 Year Study of Spectral Variability in NGC 5548

We present the final installment of an intensive 13 year study of variations of the optical continuum and broad Hemission line in the Seyfert 1 galaxy NGC 5548. The database consists of 1530 optical continuum measurements and 1248 Hmeasurements. The Hvariations follow the continuum variations closely, with a typical time delay of about 20 days. However, a year-by-year analysis shows that the magnitude of emission-line time delay is correlated with the mean continuum flux. We argue that the data are consistent with the simple model prediction between the size of the broad-line region and the ionizing luminosity, r / L 1=2 ion . Moreover, the apparently linear nature of the correlation between the Hresponse time and the nonstellar optical continuum Fopt arises as a consequence of the changing shape of the continuum as it varies, specifically Fopt / F 0:56 UV . Subject headings: galaxies: active — galaxies: individual (NGC 5548) — galaxies: nuclei — galaxies: Seyfert

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. XI. Intensive monitoring of the ultraviolet spectrum of NGC 7469

From 1996 June 10 to July 29, the International Ultraviolet Explorer monitored the Seyfert 1 galaxy NGC 7469 continuously in an attempt to measure time delays between the continuum and emission-line fluxes. From the time delays, one can estimate the size of the region dominating the production of the UV emission lines in this source. We find the strong UV emission lines to respond to continuum variations with time delays of about 23-31 for Lyα, 27 for C IV λ1549, 19-24 for N V λ1240, 17-18 for Si IV λ1400, and 07-10 for He II λ1640. The most remarkable result, however, is the detection of apparent time delays between the different UV continuum bands. With respect to the UV continuum flux at 1315 A, the flux at 1485 A, 1740 A, and 1825 A lags with time delays of 021, 035, and 028, respectively. Determination of the significance of this detection is somewhat problematic since it depends on accurate estimation of the uncertainties in the lag measurements, which are difficult to assess. We attempt to estimate the uncertainties in the time delays through Monte Carlo simulations, and these yield estimates of ~007 for the 1 σ uncertainties in the interband continuum time delays. Possible explanations for the delays include the existence of a continuum-flux reprocessing region close to the central source and/or a contamination of the continuum flux with a very broad time-delayed emission feature such as the Balmer continuum or merged Fe II multiplets.

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 A), and the 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 A). The optical continuum variations follow the variations in the ultraviolet and X-ray with time delays, measured from the centroids of the cross-correlation 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, and 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 profile variations are largest near line center.

Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XV. Long-Term Optical Monitoring of NGC 5548

We present the results of 3 yr of ground-based observations of the Seyfert 1 galaxy NGC 5548, which, combined with previously reported data, yield optical continuum and broad-line Hβ light curves for a total of 8 yr. The light curves consist of over 800 points, with a typical spacing of a few days between observations. During this 8 yr period, the nuclear continuum has varied by more than a factor of 7, and the Hβ emission line has varied by a factor of nearly 6. The Hβ emission line responds to continuum variations with a time delay or lag of ~10-20 days, the precise value varying somewhat from year to year. We find some indications that the lag varies with continuum flux in the sense that the lag is larger when the source is brighter.

Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XIII. Ultraviolet Observations of the Broad-Line Radio Galaxy 3C 390.3

As part of an extensive multiwavelength monitoring campaign, the International Ultraviolet Explorer satellite was used to observe the broad-line radio galaxy 3C 390.3 during the period 1994 December 31E1996 March 5. Spectra were obtained every 6E10 days. The UV continuum varied by a factor of 7 through the campaign, while the broad emission lines varied by factors of 2E5. Unlike previously moni- tored Seyfert 1 galaxies, in which the X-ray continuum generally varies with a larger amplitude than the UV, in 3C 390.3 the UV continuum light curve is similar in both amplitude and shape to the X-ray light curve observed by ROSAT . The UV broad emission-line variability lags that of the UV continuum by 35E70 days for Lya and C IV, values larger than those found for Seyfert 1 galaxies of comparable UV luminosity. These lags are also larger than those found for the Balmer lines in 3C 390.3 over the same period. The red and blue wings of C IV and Lya vary in phase, suggesting that radial motion does not dominate the kinematics of the UV line-emitting gas. Comparison with archival data provides evidence for velocity-dependent changes in the Lya and C IV line pro-les, indicating evolution in the detailed properties and/or distribution of the broad-line emitting gas. Subject headings: galaxies: active E galaxies: individual (3C 390.3) E ultraviolet: galaxies

Variations of the ultraviolet Fe II and Balmer continuum emission in the Seyfert galaxy NGC 5548

We present measurements of the Balmer continuum/Fe II emission blend between 2160 and 4130 A in the Seyfert galaxy NGC 5548. The measurements are from spectra obtained as part of the combined space-based and ground-based monitoring program of this object in 1988-1989. An iterative scheme is used to determine and subtract the continuum emission underlying the emission blend so as to obtain a light curve sampled once every four days. The small blue bump is an important component of the emission-line cooling, constituting about one third of the line flux in this object. Its flux varies with an amplitude of approximately +/- 20 percent about the mean, similar to the amplitude of the Balmer line variations during the same period. Its light curve resembles that of Ly-alpha, with a lag of about 10 days behind the continuum variations. The bump variation amplitude is independent of the wavelength interval where it is measured, which indicates that both the Balmer continuum and Fe II emission have comparable variation amplitudes. These results suggest that the Fe II UV multiplets and the Balmer continuum are emitted in the same parts of the broad-line region as most other broad emission lines in this object.

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. IV - Intensity variations of the optical emission lines of NGC 5548

Measurements of optical emission-line flux variations based on spectra of the Seyfert galaxy NGC 5548 obtained between December 1988 and October 1989 are reported. All of the measured optical emission lines, H-alpha, H-beta, H-gamma, He I 5876, and He II 4686, exhibit the same qualitative behavior as the UV and optical continua, but with short time delays, or lags, which are different for the various lines. Cross-correlation analysis is applied to measure the lags between the various lines and the continuum. Similar lags are found with respect to the UV continuum for H-alpha and H-beta, 17 and 19 d, respectively. The lag for H-gamma is shorter (13 d), only somewhat larger than the lag measured for Ly-alpha (about 10 d). The helium lines respond to continuum variations more rapidly than the hydrogen lines, with lags of about 7 d for He II 4686 and 11 d for He I 5876.

Intermediate resolution Hβ spectroscopy and photometric monitoring of 3C 390.3 I. Further evidence of a nuclear accretion disk

We have monitored the AGN 3C 390.3 between 1995 and 2000. A historical B-band light curve dating back to 1966 shows a large increase in brightness during 1970{1971, followed by a gradual decrease down to a minimum in 1982. During the 1995{2000 lapse the broad H emission and the continuum flux varied by a factor of 3. Two large amplitude outbursts, of dierent duration, in continuum and H light were observed i.e.: in October 1994 a brighter flare that lasted1000 days and in July 1997 another one that lasted700 days were detected. The response time lag of the emission lines relative to flux changes of the continuum has been found to vary with time i.e. during 1995{1997 a lag of about 100 days is evident, while during 1998{1999 a double valued lag of100 days and35 days is present in our data. The flux in the H wings and line core vary simultaneously, a behavior indicative of predominantly circular motions in the BLR. Important changes of the H emission proles were detected: at times, we found proles with prominent asymmetric wings, like those normaly seen in Sy1s, while at other times, we observe proles with weak, almost symmetrical wings, similar to those of Sy1.8s. We further dismiss the hypothesis that the double peaked H proles in this object originate in a massive binary BH. Instead, we found that the radial velocity dierence between the red and blue bumps is anticorrelated with the light curves of H and continuum radiation. This implies that the zone that contributes most of the energy to the emitted line changes in radius within the disk. The velocity dierence increases, corresponding to smaller radii, as the continuum flux decreases. When the continuum flux increases the hump velocity dierence decreases. These transient phenomena are expected to result from the variable accretion rate close to the central source. The optical continuum and the H flux variations might be related to changes in X-ray emission modulated by a variable accretion rate, changing the surface temperature of the disk, as a result of a variable X-ray irradiation (Ulrich 2000). Theoretical H proles were computed for an accretion disk, the observed proles are best reproduced by an inclined disk (25) whose region of maximum emission is located roughly at 200 Rg .T he mass of the black hole in 3C 390.3, estimated from the reverberation analysis is Mrev 2:1 10 9 M, 5 times larger than previous

Steps toward determination of the size and structure of the broad-line region in active nuclei. 7: Variability of the optical spectrum of NGC 5548 over 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 H(beta) 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 H(beta) transfer functions for each of the 4 yr and for the entire 4 yr database are derived by using a maximum entropy method.