Examinando por Autor "Vagnetti, F."
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Ítem A structure function analysis of VST-COSMOS AGN(EDP Sciences, 2022-08) De Cicco, D.; Bauer, F.E.; Paolillo, M.; Sánchez-Sáez, P.; Brandt, W.N.; Vagnetti, F.; Pignata, G.; Radovich, M.; Vaccari, M.Context. We present our sixth work in a series dedicated to variability studies of active galactic nuclei (AGN), based on the survey of the COSMOS field by the VLT Survey Telescope (VST). Its 54 r-band visits over 3.3 yr and single-visit depth of 24.6 r-band mag make this dataset a valuable scaled-down version that can help forecast the performance of the Rubin Observatory Legacy Survey of Space and Time (LSST). Aims. This work is centered on the analysis of the structure function (SF) of VST-COSMOS AGN, investigating possible differences in its shape and slope related to how the AGN were selected, and explores possible connections between the AGN ensemble variability and the black-hole mass, accretion rate, bolometric luminosity, redshift, and obscuration of the source. Given its features, our dataset opens up the exploration of samples ∼2 mag fainter than most literature to date. Methods. We identified several samples of AGN "677 in total "obtained through a variety of selection techniques partly overlapping. Our analysis compares the results for the various samples. We split each sample in two based on the median of the physical property of interest, and analyzed the differences in the SF shape and slope, and their possible causes. Results. While the SF shape does not change with depth, it is highly affected by the type of AGN (unobscured or obscured) included in the sample. Where a linear region can be identified, we find that the variability amplitude is anticorrelated to the accretion rate and bolometric luminosity, consistent with previous literature on the topic, while no dependence on black-hole mass emerges from this study. With its longer baseline and denser and more regular sampling, the LSST will allow for an improved characterization of the SF and its dependencies on the mentioned physical properties over much larger AGN samples. ©Ítem Extending the variability selection of active galactic nuclei in the W-CDF-S and SERVS/SWIRE region(EDP Sciences, 2020-02) Poulain, M.; Paolillo, M.; De Cicco, D.; Brandt, W.N; Bauer, , F. E.; Falocco, S.; Vagnetti, F.; Grado, A.; Ragosta, F.; Botticella, M. T.; Cappellaro, E.; Pignata, G.; Vaccar, M.; Schipani, P.; Covone, G.; Longo, G.; Napolitano, N. R.Context. Variability has proven to be a powerful tool to detect active galactic nuclei (AGN) in multi-epoch surveys. The new-generation facilities expected to become operational in the next few years will mark a new era in time-domain astronomy and their wide-field multi-epoch campaigns will favor extensive variability studies. Aims. We present our analysis of AGN variability in the second half of the VST survey of the Wide Chandra Deep Field South, performed in the r band and covering a 2 sq. deg area. The analysis complements a previous work, in which the first half of the area was investigated. We provide a reliable catalog of variable AGN candidates, which will be critical targets in future variability studies. Methods. We selected a sample of optically variable sources and made use of infrared data from the Spitzer mission to validate their nature by means of color-based diagnostics. Results. We obtain a sample of 782 AGN candidates among which 12 are classified as supernovae, 54 as stars, and 232 as AGN. We estimate a contamination 20% and a completeness ∼38% with respect to mid-infrared selected samples. © ESO 2020.Ítem SUDARE-VOICE variability-selection of active galaxies in the Chandra Deep Field South and the SERVS/SWIRE region(EDP Sciences, 2015-07) Falocco, S.; Paolillo, M.; Covone, G.; De Cicco, D.; Longo, G.; Grado, A.; Limatola, L.; Vaccari, M.; Botticella, M.T.; Pignata, G.; Cappellaro, E.; Trevese, D.; Vagnetti, F.; Salvato, M.; Radovich, M.; Hsu, L.; Capaccioli, M.; Napolitano, N.; Brandt, W.N.; Baruffolo, A.; Cascone, E.; Schipani, P.One of the most peculiar characteristics of active galactic nuclei (AGNs) is their variability over all wavelengths. This property has been used in the past to select AGN samples and is foreseen to be one of the detection techniques applied in future multi-epoch surveys, complementing photometric and spectroscopic methods. Aims. In this paper, we aim to construct and characterise an AGN sample using a multi-epoch dataset in the r band from the SUDARE-VOICE survey. Methods. Our work makes use of the VST monitoring programme of an area surrounding the Chandra Deep Field South to select variable sources. We use data spanning a six-month period over an area of 2 square degrees, to identify AGN based on their photometric variability. Results. The selected sample includes 175 AGN candidates with magnitude r< 23 mag. We distinguish different classes of variable sources through their lightcurves, as well as X-ray, spectroscopic, SED, optical, and IR information overlapping with our survey. Conclusions. We find that 12% of the sample (21/175) is represented by supernovae (SN). Of the remaining sources, 4% (6/154) are stars, while 66% (102/154) are likely AGNs based on the available diagnostics. We estimate an upper limit to the contamination of the variability selected AGN sample a 34%, but we point out that restricting the analysis to the sources with available multi-wavelength ancillary information, the purity of our sample is close to 80% (102 AGN out of 128 non-SN sources with multi-wavelength diagnostics). Our work thus confirms the efficiency of the variability selection method, in agreement with our previous work on the COSMOS field. In addition we show that the variability approach is roughly consistent with the infrared selection. © ESO, 2015.Ítem Variability-selected active galactic nuclei in the VST-SUDARE/VOICE survey of the COSMOS field(EDP Sciences, 2015-02) De Cicco, D.; Paolillo, M.; Covone, G.; Falocco, S.; Longo, G.; Grado, A.; Limatola, L.; Botticella, M.T.; Pignata, G.; Cappellaro, E.; Vaccari, M.; Trevese, D.; Vagnetti, F.; Salvato, M.; Radovich, M.; Brandt, W.N.; Capaccioli, M.; Napolitano, N.R.; Schipani, P.Context. Active galaxies are characterized by variability at every wavelength, with timescales from hours to years depending on the observing window. Optical variability has proven to be an effective way of detecting AGNs in imaging surveys, lasting from weeks to years. Aims. In the present work we test the use of optical variability as a tool to identify active galactic nuclei in the VST multiepoch survey of the COSMOS field, originally tailored to detect supernova events. Methods. We make use of the multiwavelength data provided by other COSMOS surveys to discuss the reliability of the method and the nature of our AGN candidates. Results. The selection on the basis of optical variability returns a sample of 83 AGN candidates; based on a number of diagnostics, we conclude that 67 of them are confirmed AGNs (81% purity), 12 are classified as supernovae, while the nature of the remaining 4 is unknown. For the subsample of AGNs with some spectroscopic classification, we find that Type 1 are prevalent (89%) compared to Type 2 AGNs (11%). Overall, our approach is able to retrieve on average 15% of all AGNs in the field identified by means of spectroscopic or X-ray classification, with a strong dependence on the source apparent magnitude (completeness ranging from 26% to 5%). In particular, the completeness for Type 1 AGNs is 25%, while it drops to 6% for Type 2 AGNs. The rest of the X-ray selected AGN population presents on average a larger rms variability than the bulk of non-variable sources, indicating that variability detection for at least some of these objects is prevented only by the photometric accuracy of the data. The low completeness is in part due to the short observing span: we show that increasing the temporal baseline results in larger samples as expected for sources with a red-noise power spectrum. Our results allow us to assess the usefulness of this AGN selection technique in view of future wide-field surveys. © 2015 ESO.