Astrophysical: Quasars

  • Publication
    On the Reliability of Microvariability Tests in Quasars
    Microvariations probe the physics and internal structure of quasars. Unpredictability and small flux variations make this phenomenon elusive and difficult to...
  • Publication
    On the use of photometric redshifts for X-ray selected AGNs
    In this paper we present photometric redshift estimates for a sample of X-ray selected sources detected in the wide-field ( 2 deg^2), bright [ f_X(0.5{-}8 keV)...
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    Optical and Near-Infrared Calibration of AGN Field Stars: An All-Sky Network of Faint Stars Calibrated on the Landolt System
    We present a total of 12,436 photometric measures of 371 field stars of 26 quasars in the visible (UBVRI) and 22,276 photometric measures of 122 field stars of...
  • Publication
    Optical and near-infrared imaging of faint Gigahertz Peaked Spectrum sources
    A sample of 47 faint Gigahertz Peaked Spectrum (GPS) radio sources selected from the Westerbork Northern Sky Survey (WENSS) has been imaged in the optical and...
  • Publication
    Optical and X-ray properties of the RIXOS AGN - II. Emission lines
    We present the optical and UV emission-line properties of 160 X-ray-selected active galactic nuclei (AGN) taken from the RIXOS survey (including Hα, Hβ, [Oiii]...
  • Publication
    Optical Counterparts of Ultraluminous X-Ray Sources
    We present the optical identification and characterization of counterparts of four objects previously cataloged as ultraluminous X-ray (ULX) sources. The...
  • Publication
    Optical Microvariability in Quasars: Spectral Variability
    We present a method that we developed to discern where the optical microvariability (OM) in quasars originates: in the accretion disk (related to thermal...
  • Publication
    Optical microvariability of bright type 2 quasars
    We present results from a project focused on searching optical microvariabilty (also known as ``intra-night'' variability) in type 2 - obscured - quasars...
  • Publication
    Optical Photometry of Quasar 0957+561A, B
    Observations of the gravitational lens system 0957+561A, B in the R band are presented in this Letter. The observations, taken with the 82 cm IAC-80 telescope...