G. M. Stirpe

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. 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

BeppoSAX observations of Narrow-Line Seyfert 1 galaxies - II. Ionized iron features in Arakelian 564

The BeppoSAX observations of the bright Narrow-Line Seyfert 1 galaxy Ark 564 are presented along with a high quality optical spectrum taken at the 1.5m telescope at La Silla. The 0.1-10 keV X-ray spectrum is characterized by a strong soft component which is best described by blackbody-like emission with a temperature of about 160 eV. At higher energies a steep (Gamma = 2.4) power-law tail is present. There is evidence of an ionized reflector in the form of an iron line and edge. We do not find significant evidence of soft X-ray features if the spectrum is modelled with a two component continuum. The optical and X-ray spectral properties support the hypothesis of a high accretion rate onto a low mass black hole.We report on the first spectrum up to 10 keV of the bright narrow-line Seyfert 1 galaxy Ton S 180, obtained with the imaging instruments onboard BeppoSAX. This is the first observed source in a sample of a dozen narrow-line Seyfert 1 galaxies in the BeppoSAX Core Program. We also present and discuss a high quality optical spectrum taken at the 1.5 m tele- scope at La Silla two months before the BeppoSAX observation. The X-ray spectrum shows a clear hardening above about 2 keV, where a power law with 2:3 plus an iron line provide a good description of the data. This slope is significantly steeper than the typical one for classical Seyfert 1s and quasars. The best fit line energy is suggestive of highly ionized iron, which would support the idea that the high accretion rate is (one of) the fundamental parameter(s) characterizing the Narrow Line Seyfert 1 phenomenon.

The Complex X-Ray Absorbers of NGC 3516 Observed by BEPPOSAX

In this paper we present the analysis of two broadband (0.1-150 keV) BeppoSAX observations of the Seyfert 1 galaxy NGC 3516. The two observations were taken 4 months apart, on 1996 November 8 and 1997 March 12. We report a dramatic change in the degree of obscuration of the central source between the two observations and propose, as possible explanations, transient absorption by either a stationary-state cloud of cold gas crossing the line of sight or a varying-state, initially neutral and dense amount of expanding gas with decreasing density and therefore decreasing opacity. We also report the detection of a second highly ionized absorber/emitter, which causes deep Fe XVII-XXII K edges at ~7.8 keV to appear in both of the BeppoSAX spectra of NGC 3516 and possibly produces the soft X-ray continuum emission in the 1 keV blend of Fe L recombination lines detected during the epoch of heavy nuclear obscuration.

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

BeppoSAX observations of luminous IRAS galaxies

Abstract We have obtained hard X-ray spectra of four luminous IRAS galaxies, which were selected on the basis of their optical polarized broad lines. We have found prominent Fe K line emission from IRAS 20210+1121, suggesting that its observed X-ray continuum is scattered emission from a completely blocked AGN. The X-ray-[OIII]λ5007 ratios of our sources are in the range of moderately or heavily absorbed Seyfert 2s.

BeppoSAX observations of the Seyfert 1 galaxy NGC 3516

Abstract We present the results of two observations of the bright Seyfert 1 galaxy NGC 3516, obtained with BeppoSAX in 1996 November and 1997 March. Useful signal is detected between 0.2 and 60 keV, allowing for the first time the simultaneous observation of all main spectral features. The source was brighter by a factor 2 at the second epoch of observation. Both spectra present a strong Fe Kα line, and a reflection hump at high energy. An absorption edge at 0.8 keV is visible in the later spectrum, but not in the earlier one, indicating that this feature is strongly variable.