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Popovic L.C.,Group for Astrophysical Spectroscopy | Popovic L.C.,Isaac Newton Institute of Chile | Jovanovic P.,Group for Astrophysical Spectroscopy | Jovanovic P.,Isaac Newton Institute of Chile | And 12 more authors.
Astronomy and Astrophysics | Year: 2012

Context. We study the photocenter position variability caused by variations in the quasar inner structure. We consider the variability in the accretion disk emissivity and torus structure variability caused by the different illumination by the central source. We discuss the possible detection of these effects by Gaia. Observations of the photocenter variability in two AGNs, SDSS J121855+020002 and SDSS J162011+1724327 have been reported and discussed. Aims. For variations in the quasar inner structure, we explore how much this effect can affect the position determination and whether it can (or not) be detected with the Gaia mission. Methods. We use models of (a) a relativistic disk, including the perturbation that can increase the brightness of part of the disk, and consequently offset the photocenter position, and (b) a dusty torus that absorbs and re-emits the incoming radiation from the accretion disk (central continuum source). We estimate the value of the photocenter offset caused by these two effects. Results. We found that perturbations in the inner structure can cause a significant offset to the photocenter. This offset depends on the characteristics of both the perturbation and accretion disk and on the structure of the torus. In the case of the two considered QSOs, the observed photocenter offsets cannot be explained by variations in the accretion disk and other effects should be considered. We discuss the possibility of exploding stars very close to the AGN source, and also that there are two variable sources at the center of these two AGNs that may indicate a binary supermassive black hole system on a kpc (pc) scale. Conclusions. The Gaia mission seems to be very promising, not only for astrometry, but also for exploring the inner structure of AGNs. We conclude that variations in the quasar inner structure can affect the observed photocenter (by up to several mas). There is a chance to observe such an effect in the case of bright and low-redshift QSOs. © 2012 ESO.

Popovic L.C.,Group for Astrophysical Spectroscopy | Popovic L.C.,Isaac Newton Institute of Chile | Kovacevic J.,Group for Astrophysical Spectroscopy | Kovacevic J.,Isaac Newton Institute of Chile
Astrophysical Journal | Year: 2011

We divide a sample of 302 type-1 active galactic nuclei into two subsamples based on the narrow-line [O III]/HβNLR ratio, expecting that there will be a stronger starburst (H II region) contribution to the narrow-line emission for R= log([O III]/HβNLR) < 0.5. For both samples, we find significant differences in correlations between spectral properties of objects with R < 0.5 and R > 0.5. We find similar differences when we divide the sample based on the FWHM ratios of [O III] and broad Hβ lines (R 1 = log (FWHM [O III]/FWHM Hβbroad)> < - 0.8), i.e., similar correlations between R > 0.5 and R 1 < -0.8 subsamples from one side and R < 0.5 and R 1 > -0.8 subsamples from the other side. The most interesting difference is in the correlation between the broad Hβ FWHM and luminosity in the R < 0.5 (R 1 > -0.8) sample, which indicates a connection between the broad-line region kinematics and the photoionization source. We discuss possible effects that can cause these differences in spectral properties of two subsamples. © 2011. The American Astronomical Society. All rights reserved.

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