Optical monitoring of quasars – I. Variability |
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| Authors: | Aurea Garcia Laerte Sodré Jr Francisco J Jablonski Roberto J Terlevich † |
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| Institution: | Departamento de Astronomia, Instituto Astronômico e Geofúsico da USP, Av. Miguel Stefano 4200, 04301-904 São Paulo, Brazil; Departamento de AstrofísicáINPE/MCT, CP151, 12201 São Josédos Campos, Brazil; Institute of Astronomy, Madingley Road, Cambridge CB3 OHA |
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| Abstract: | We present an analysis of quasar variability from data collected during a photometric monitoring of 50 objects carried out at CNPq/Laboratório Nacional de Astrofísicá, Brazil, between 1993 March and 1996 July. A distinctive feature of this survey is its photometric accuracy, ∼0.02 V mag, achieved through differential photometry with CCD detectors, which allows the detection of faint levels of variability. We find that the relative variability, δ σ L , observed in the V band is anticorrelated with both luminosity and redshift, although we have no means of discovering the dominant relation, given the strong coupling between luminosity and redshift for the objects in our sample. We introduce a model for the dependence of quasar variability on frequency that is consistent with multiwavelength observations of the nuclear variability of the Seyfert galaxy NGC 4151. We show that correcting the observed variability for this effect slightly increases the significance of the trends of variability with luminosity and redshift. Assuming that variability depends only on the luminosity, we show that the corrected variability is anticorrelated with luminosity and is in good agreement with predictions of a simple Poissonian model. The energy derived for the hypothetical pulses, ∼1050 erg, agrees well with those obtained in other studies. We also find that the radio-loud objects in our sample tend to be more variable than the radio-quiet ones, for all luminosities and redshifts. |
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| Keywords: | methods: statistical techniques: photometric galaxies: active quasars: general |
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