Showing papers by "Maria Santos-Lleo published in 1997"
Goddard Space Flight Center1, University of St Andrews2, Johns Hopkins University3, University of California, Los Angeles4, Tel Aviv University5, University of Leicester6, Ohio State University7, California Institute of Technology8, University of Michigan9, University of California, Berkeley10, University of Florida11, University of Geneva12, York University13, Universidade Federal do Rio Grande do Sul14, University of Iowa15, University of Nebraska–Lincoln16, Harvard University17, National Research Council18, Space Telescope Science Institute19, University of Kentucky20, Technion – Israel Institute of Technology21, University of Toronto22, Bowling Green State University23, University of Oviedo24, Spanish National Research Council25, University of Edinburgh26, National Institute of Standards and Technology27, University of Wisconsin-Madison28, National Central University29
TL;DR: In this article, an 8-month monitoring campaign on the Seyfert 1 galaxy Fairall 9 has been conducted with the International Ultraviolet Explorer in an attempt to obtain reliable estimates of continuum-continuum and continuum-emission-line delays for a high-luminosity active galactic nucleus (AGN).
Abstract: An 8 month monitoring campaign on the Seyfert 1 galaxy Fairall 9 has been conducted with the International Ultraviolet Explorer in an attempt to obtain reliable estimates of continuum-continuum and continuum-emission-line delays for a high-luminosity active galactic nucleus (AGN). While the results of this campaign are more ambiguous than those of previous monitoring campaigns on lower luminosity sources, we find general agreement with the earlier results: (1) there is no measurable lag between ultraviolet continuum bands, and (2) the measured emission-line time lags are very short. It is especially notable that the Ly? + N V emission-line lag is about 1 order of magnitude smaller than determined from a previous campaign by Clavel, Wamsteker, & Glass (1989) when Fairall 9 was in a more luminous state. In other well-monitored sources, specifically NGC 5548 and NGC 3783, the highest ionization lines are found to respond to continuum variations more rapidly than the lower ionization lines, which suggests a radially ionization-stratified broad-line region. In this case, the results are less certain, since none of the emission-line lags are very well determined. The best-determined emission line lag is Ly? + N V, for which we find that the centroid of the continuum-emission-line cross-correlation function is ?cent ? 14-20 days. We measure a lag ?cent 4 days for He II ?1640; this result is consistent with the ionization-stratification pattern seen in lower luminosity sources, but the relatively large uncertainties in the emission-line lags measured here cannot rule out similar lags for Ly? + N V and He II ?1640 at a high level of significance. We are unable to determine a reliable lag for C IV ?1550, but we note that the profiles of the variable parts of Ly? and C IV ?1550 are not the same, which does not support the hypothesis that the strongest variations in these two lines arise in the same region.
210 citations
Ohio State University1, University of St Andrews2, University of Colorado Boulder3, European Space Agency4, Goddard Space Flight Center5, Johns Hopkins University6, University of California, Los Angeles7, Tel Aviv University8, University of Leicester9, Max Planck Society10, New Mexico State University11, National Autonomous University of Mexico12, Sternberg Astronomical Institute13, Russian Academy of Sciences14, University of California, Berkeley15, University of Nebraska–Lincoln16, Universities Space Research Association17, Space Telescope Science Institute18, Harvard University19, University of Kentucky20, Technion – Israel Institute of Technology21, University of Michigan22, Dominion Astrophysical Observatory23, Bowling Green State University24, Spanish National Research Council25, National Institute of Standards and Technology26, University of Wisconsin-Madison27, National Central University28, European Southern Observatory29, University of Texas at Austin30, Chinese Academy of Sciences31
TL;DR: In this article, 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.
Abstract: 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.
172 citations
01 Jan 1997
TL;DR: In this paper, 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.
Abstract: 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.
120 citations
Posted Content•
TL;DR: In this paper, the authors analyzed new and archival IUE observations of narrow-line Seyfert 1 galaxies (NLS1) in order to revise the ultraviolet (UV) properties of this sub-group of Active Galactic Nuclei (AGN).
Abstract: We have analyzed new and archival IUE observations of narrow-line Seyfert 1 galaxies (NLS1) in order to revise the ultraviolet (UV) properties of this sub-group of Active Galactic Nuclei (AGN). We have found broad wings in the strongest UV emission lines, ruling out the hypothesis that there is no broad line emission region in this type of objects. Since the similarities in spectral energy distributions from the far-infrared (FIR) to the soft X rays in both narrow-line and broad-line Seyfert 1 galaxies do not suggest that the nuclei of NLS1 are hidden from a direct view, we discuss the possibility that the line emitting material in NLS1 is optically thin.
2 citations
Journal Article•
TL;DR: In this article, the authors have analyzed new and archived IUE observations of narrow-line Seyfert 1 galaxies (NLS1) in order to revise the ultraviolet (UV) properties of this sub-group of Active Galactic Nuclei (AGN).
Abstract: WehaveanalyzednewandarchivalIUEobservations of narrow-line Seyfert 1 galaxies (NLS1) in order to revise the ultraviolet (UV) properties of this sub-group of Active Galactic Nuclei (AGN). We have found broad wings in the strongest UV emission lines, ruling out the hypothesis that there is no broad lineemissionregioninthistypeofobjects.Sincethesimilarities inspectralenergydistributionsfromthefar-infrared(FIR)tothe softXraysinbothnarrow-lineandbroad-lineSeyfert 1galaxies do not suggest that the nuclei of NLS1 are hidden from a direct view, we discuss the possibility that the line emitting material in NLS1 is optically thin.
2 citations