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We present the characterization and initial results from the QUEST–La Silla active galactic nucleus AGNvariability survey. This is an effort to obtain well-sampled optical light curves in extragalactic fields with uniquemultiwavelength observations. We present photometry obtained from 2010 to 2012 in the XMM-COSMOS field,which was observed over 150 nights using the QUEST camera on the European Southern ObservatoryESO Schmidt telescope. The survey uses a broadband filter, the Q band, similar to the union of the g and the rfilters, achieving an intrinsic photometric dispersion of 0.05 mag and a systematic error of 0.05 mag in thezero point. Since some detectors of the camera show significant nonlinearity, we use a linear correlation to fit thezero points as a function of the instrumental magnitudes, thus obtaining a good correction to the nonlinear behaviorof these detectors. We obtain good photometry to an equivalent limiting magnitude of r ~ 20.5. The astrometryhas an internal precision of ~ 0. 1 and an overall accuracy of 0. 2 when compared to the Sloan Digital Sky Survey.Studying the optical variability of X-ray-detected sources in the XMM-COSMOS field, we find that the survey is∼75%–80% complete to magnitudes r ~ 20, and ∼67% complete to a magnitude r ~ 21. Additionally, broad-lineBL AGNs have larger variation amplitude than non-broad-line NL AGNs, with ∼80% of the BL AGNsclassified as variable, while only ∼21% of the NL AGNs are classified as variable. We also find that ∼22% ofobjects classified as galaxies GALs are also variable. The determination and parameterization of the structurefunction SFnorm t t = A g of the variable sources show that most BL AGNs are characterized by A > 0.1 andg > 0.025. It is further shown that NL AGNs and GAL sources occupying the same parameter space in A and γ arevery likely to correspond to obscured or low-luminosity AGNs. Our samples are, however, small, and we expect torevisit these results using larger samples with longer light curves obtained as part of our ongoing surveyNota general

Artículo de publicación ISI

Author: Cartier Ugarte, Regis; - Lira Teillery, Paulina; - Coppi, Paolo; - Sánchez, Paula; - Arévalo, Patricia; - Bauer, Franz; - Rabin



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