We present the results of a monitoring campaign of the AGN in NGC 3227, conducted at La Palma by the LAG european consortium. The data are long slit spectra, obtained with the 1.5m INT and 4.2m WHT, from January to June 1990. The slit width was 1.5 arcsec. The spectral resolution was about 3 A.

We discuss in this paper the various sources of uncertainty which arise in the relative scaling of spectroscopic data sets obtained on active galactic nuclei. The case is illustrated for NGC 3227, one of the targets monitored during the LAG campaign, and the errors derived have been attached to the final results discussed by Salamanca et al. (1993). We examine the effects of slit miscentering, of differences in the atmospheric seeing and finally of the line deblending procedure.

We present in this work the results of a five-month monitoring campaign of the active galactic nucleus in NGC 3227. Both the Balmer Hbeta and Halpha emission lines, as well as the optical continuum have been analysed. A deblending procedure has been applied which allows to separate the contributions to the line emission from the narrow line region (NLR) on one side and from the broad line region (BLR) on the other side. The stellar contribution to the observed continuum within a 1.5 x 4 arcsec2 slit is found to be in the range 24-40% when the AGN is in the lowest state of activity observed during this monitoring period. The largest source of uncertainty in deriving the light-curves of the BLR emission and of the AGN continuum emission comes from differences in the seeing conditions prevailing at the various observational epochs. We have applied a correction factor for this effect. The optical AGN continuum and the BLR emission in NGC 3227 appear to vary by about 40% on a timescale of 1.5 month. We have followed a burst with maximum around early March and minimum by mid-April 1990. The levels of the broad line emission and the lambda6750 continuum are well correlated, a fact consistent with the classical assumption that the BLR material is photoionized by the central continuum source. Cross-correlation analyses between the light-curves of the lambda6750 AGN continuum and the BLR Halpha emission indicate that the lag of the BLR emission with respect to the continuum variations is 17 +/- 7 d. This result suggests that the BLR clouds which are affected by changes in the flux level of the central ionizing source lie about 17 light-days away. The variable part of the Halpha line shows a flat-topped profile with FWHM approximately 2900 km s-1. Within the observed range of continuum fluctuations (approximately 40%), the broad wings of the Halpha emission line do not vary in a noticeable way. This implies either that the BLR clouds building up the wings remain fully ionized during the continuum variations or that the time sampling should be increased if one wished to measure such an effect. Introduced together with other AGN in the plane {Balmer lag, luminosity}, NGC 3227 contributes to define a relationship slightly less steep than the BLR size scaling as the square root of the absolute luminosity.

This study presents the results of a multiwavelength monitoring of the active galactic nucleus in NGC 1566. Data collected in the X-rays, ultraviolet, visible and near-infrared domains have been combined together, in order to disentangle the various components and to better understand the patterns of variability in this active nucleus. At all wavelengths covered by this study the continuous emission is found to vary. The soft X-rays vary by 40% on a time scale shorter than a month. The spectrum of the variable component, as it appears along an outburst which developed over 6 months, can be represented by a power law with index beta approximately 1.5 from the near infrared to the ultraviolet and beta < 1 at higher frequencies. This does not imply however that we are dealing here with a single physical process. The BLR appears to be in an ionization-bounded situation. Profile study of lines arising from the NLR shows that this region has complex structure and kinematics. Analysis of the near infrared variable component leads to the following conclusions: (i) from its spectral shape, we derive that the variable near infrared emission is consistent with thermal radiation from hot graphite particles approximately at their evaporation temperature T(d) approximately 1500 K; (ii) the mass of dust related to the variable near infrared emission is 7 10(-4) M.; (iii) assuming that the dust particles are heated by the central ultraviolet source, the energy balance in the close environment of the active nucleus tells us that the dust covering factor is approximately 0.6; (iv) the time lag between the near infrared and ultraviolet high-curves, along an intense outburst, is found to be of 2 +/- 1 month while the bursts themselves are of comparable width; and (v) given the ultraviolet luminosity of the active nucleus, the dust particles would be located at the evaporation radius r(e) approximately 7 light-weeks. Therefore, the emergent picture is that the BLR is associated with or just surrounded by an ensemble of graphite particles heated by the central ultraviolet source, at a radius around 2 light-months. The active nucleus of NGC 1566, interpreted in terms of the black hole model, radiates at less than one hundredth its Eddington luminosity and appears to be a scaled-down version of the other active nucleus F9 in which, similarly, a hot dust component has been detected close to the BLR.

view Abstract Citations (502) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. I. an 8 Month Campaign of Monitoring NGC 5548 with IUE Clavel, J. ; Reichert, G. A. ; Alloin, D. ; Crenshaw, D. M. ; Kriss, G. ; Krolik, J. H. ; Malkan, M. A. ; Netzer, H. ; Peterson, B. M. ; Wamsteker, W. ; Altamore, A. ; Baribaud, T. ; Barr, P. ; Beck, S. ; Binette, L. ; Bromage, G. E. ; Brosch, N. ; Diaz, A. I. ; Filippenko, A. V. ; Fricke, K. ; Gaskell, C. M. ; Giommi, P. ; Glass, I. S. ; Gondhalekar, P. ; Hackney, R. L. ; Halpern, J. P. ; Hutter, D. J. ; Joersaeter, S. ; Kinney, A. L. ; Kollatschny, W. ; Koratkar, A. ; Korista, K. T. ; Laor, A. ; Lasota, J. -P. ; Leibowitz, E. ; Maoz, D. ; Martin, P. G. ; Mazeh, T. ; Meurs, E. J. A. ; Nair, A. D. ; O'Brien, P. ; Pelat, D. ; Perez, E. ; Perola, G. C. ; Ptak, R. L. ; Rodriguez-Pascual, P. ; Rosenblatt, E. I. ; Sadun, A. C. ; Santos-Lleo, M. ; Shaw, R. A. and 7 more Abstract We present emission-line and ultraviolet continuum observations of a type I Seyfert galaxy in which the time resolution is adequate for describing the character of variability. Using the IUE satellite, the nucleus of NGC 5548 was observed every 4 days for a period of 8 months. Its mean properties-continuum shape, line ratios-are not unusual for type I Seyfert galaxies, but it was found to be strongly variable. The ultraviolet continuum flux and broad emission line fluxes varied significantly, going through three large maxima and three deep minima. The ratio of maximum to minimum flux was ~ 4.5 for the continuum at 1350 A, and the continuum was significantly bluer when it was brighter. The high ionization emission lines showed the strongest variations, with N V λ1240 and He II λ1640 exhibiting maximum-to-minimum flux ratios as high as those of the continuum. Intermediate-ionization lines, including Lyα λ1216, C IV λ1549, and C II] λ1909, had maximum- to-minimum amplitudes of ~ 2, and Mg II λ2798, the lowest ionization line, exhibited the smallest amplitude fluctuations, ~ 1.3. The great majority of all variations were well resolved in time. Apart from Mg II λ2798, the emission-line variations correlate extremely well with those of the 1350 A continuum if allowance is made for a systematic delay, lending qualitative support to the view that photoionization by the nuclear continuum is responsible for driving the emission lines. The delay of a given line seems to depend on the degree of ionization of its species. The He II λ1640 and N V λ1240 features exhibit the shortest delay. {DELTA}t ~ 4-10 days, while the Lyα λ1216 and C IV λ1549 lines yield 8-16 days. The Si IV + O IV] λ1402 feature and the C III] λ1909 line exhibit significantly larger delays, between 12 and 34 days. In the case of Mg II λ2798, the cross-correlation is broad and shallow, so that the delay is not only loosely constrained. {DELTA}t ~ 34-72 days. Publication: The Astrophysical Journal Pub Date: January 1991 DOI: 10.1086/169540 Bibcode: 1991ApJ...366...64C Keywords: Active Galactic Nuclei; Astronomical Spectroscopy; Galactic Structure; Iue; Seyfert Galaxies; Emission Spectra; Time Series Analysis; Ultraviolet Spectra; Variability; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 5548; GALAXIES: NUCLEI; GALAXIES: SEYFERT; ULTRAVIOLET: SPECTRA full text sources ADS | data products SIMBAD (1) NED (1) MAST (1) INES (1) Related Materials (14) Part 2: 1991ApJ...368..119P Part 3: 1992ApJ...392..470P Part 4: 1993ApJ...408..416D Part 5: 1994ApJ...425..582R Part 6: 1994ApJ...425..609S Part 7: 1994ApJ...425..622P Part 8: 1995ApJS...97..285K Part 9: 1997ApJS..110....9R Part 10: 1997ApJS..112..271S Part 11: 1997ApJS..113...69W Part 12: 1998ApJS..115..185D Part 13: 1998ApJ...509..163O Part 14: 1998ApJ...500..162C Part 15: 1999ApJ...510..659P

Le degre de confiance attache a la methode d'echelle qui utilise les raies d'emission [O III] de la region a raie etroite des noyaux galactiques actifs (AGN) pour determiner le niveau de continuum visible est teste a partir d'une serie de simulations spectrales de la galaxie Akn 120 dont l'AGN presente une forte emission variable des raies Fe II.

From continuum and line intensity light-curves in the ultraviolet range, we find that the CIV peak-emission lies at about 2 ± 0.5 light-month from the centre. Line profile variations in the Ha and CIV emission suggest that the BLR is made of two regions with distinct kinematical properties: •a spherically distributed set of clouds, responsible for the broad HIL emission and responding to ionizing flux variations with a time-lag of 2 light-months at most•a disc-like structure from which most of the LIL emission arises, with a slow response to ionizing flux changes: hence larger is size.