We present the final installment of an intensive 13-year study of variations of the optical continuum and broad Hβ emission line in the Seyfert 1 galaxy NGC 5548. The data base consists of 1530 optical continuum measurements and 1248 Hβ measurements. The Hβ variations 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 Hβ response time and the nonstellar optical continuum F opt arises as a consequence of the changing shape of the continuum as it varies, specifically F opt ∝ F 0.56 UV .

Abstract. Between 1996 and 2002, we have carried out a spectral monitoring program for the Seyfert galaxy NGC 5548 with the 6 m and 1 m telescopes of SAO (Russia) and with the 2.1 m telescope of Guillermo Haro Observatory (GHO) at Cananea, Mexico. High quality spectra with S /N > 50 in the continuum near Hα and Hβ were obtained, covering the spectral range ∼(4000-7500) Å with a (4.5 to 15) Å-resolution. We found that both the flux in the lines and the continuum gradually decreased, reaching minimum values during May-June 2002. In the minimum state, the wings of Hβ and Hα became extremely weak, corresponding to a Sy1.8 type, not to a Sy1, as observed previously when the nucleus was brighter. The line profiles were decomposed into variable and constant components. The variable broad component is well correlated with the continuum variation. It consists of a double peaked structure with radial velocities ∼±1000 km s −1 relative to the narrow component. A constant component, whose presence is independent of the continuum flux variations, shows only narrow emission lines.The mean, rms, and the averaged over years, observed and difference line profiles of Hβ and Hα reveal the same double peaked structure. The relative intensity of these peaks changes with time. During 1996, the red peak was the brightest, while in 1998-2002, the blue peak became the brighter one. Their radial velocities vary in the ∼(500-1200) km s −1 range. In 2000-2002 a distinct third peak appeared in the red wing of Hα and Hβ line profiles. The radial velocity of this feature decreased between 2000 and 2002: from the observed profiles, from ∼+(2500-2600) km s −1 to ∼+2000 km s −1 and is clearly seen on the difference profiles. The fluxes of the various parts of the line profiles are well correlated with each other and also with the continuum flux. The blue and red parts of the line profiles at the same radial velocities vary in an almost identical manner. Shape changes of the different parts of the broad line are not correlated with continuum variations and, apparently, are not related to reverberation effects. Changes of the integral Balmer decrement are, on average, anticorrelated with the continuum flux variations. This is probably due to an increasing role of collisional excitation as the ionizing flux decreases. The behavior of the Balmer decrement of the various parts of the line profiles was different in 1996-2000 as compared with the 2001 behavior. Our results favor the formation of the broad Balmer lines in a turbulent accretion disc with large and moving "optically thick" inhomogeneities, capable of reprocessing the central source continuum.Key words. galaxies: active -galaxies: Seyfert -galaxies: individual: NGC 5548 -line: profiles Appendices A and B are only available in elctronic form at http://www.edpsciences.org Tables 2 and 5 are only available in electronic form at the CDS via anonyous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via

Aims. We present the results of a long-term monitoring (11 years, between 1996 and 2006) of Hα and Hβ line variations of the active galactic nucleus of NGC 4151. Methods. High quality spectra (S /N > 50 and R ≈ 8 Å) of Hα and Hβ were investigated. During monitoring period, we analyzed line profile variations. Comparing the line profiles of Hα and Hβ, we studied different details (bumps, absorbtion features) in the line profiles. The variations in the different Hα and Hβ line profile segments were investigated. We also analyzed the Balmer decrement for entire lines and for line segments. Results. We found that the line profiles varied strongly during the monitoring period, and exhibited blue and red asymmetries. This is indicative of a complex BLR geometry inside NGC 4151 with, at least, three kinematically distinct regions: one that contributes to the blue line wing, one to the line core and one to the red line wing. The variation may be caused by an accelerating outflow originating very close to the black hole, where the red part may come from a region closer to the black hole than the blue part, which originates in the region with the highest outflow velocities. Conclusions. Taking into account that the BLR of NGC 4151 has a complex geometry (probably affected by an outflow) and that a portion of the broad line emission does not seem to be produced entirely by photoionization, one may ask whether the study of the BLR using reverberation mapping would be worthwhile for this galaxy.

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 Hb 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 Hb emission line has varied by a factor of nearly 6. The Hb emission line responds to continuum variations with a time delay or lag of D10È20 days, the precise value varying somewhat from year to year. We Ðnd some indications that the lag varies with continuum Ñux in the sense that the lag is larger when the source is brighter.