Examinando por Autor "Longo, G."
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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 Search for the optical counterpart of the GW170814 gravitational wave event with the VLT Survey Telescope(Oxford University Press, 2020-02) Grado, A.; Cappellaro, E.; Covino, S.; Getman, F.; Greco, G.; Limatola, L.; Yang, S.; Amati, L.; Benetti, S.; Branchesi, M.; Brocato, E.; Botticella, M.; Campana, S.; Cantiello, M.; Dadina, M.; Ammando, F. D; De Cesare, G.; D’Elia, V.; Della Valle, M.; Iodice, E.; Longo, G.; . Mapelli, M; Masetti, N.; Nicastro, L.; Palazzi, E.; Possenti, A.; Radovich, M.; Rossi, A.; Salvaterra, R.; Stella, L.; Stratta, G.; Testa, V.; Tomasella, L.We report on the search for the optical counterpart of the gravitational event GW170814, which was carried out with the VLT Survey Telescope (VST) by the GRAvitational Wave Inaf TeAm. Observations started 17.5 h after the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo alert and we covered an area of 99 deg2 that encloses ∼ 77 per cent and ∼ 59 per cent of the initial and refined localization probability regions, respectively. A total of six epochs were secured over nearly two months. The survey reached an average limiting magnitude of 22 AB mag in the r band. After assuming the model described in Perna, Lazzati & Farr, that derives as possible optical counterpart of a BBH (binary black hole) event a transient source declining in about one day, we have computed a survey efficiency of about 5 per cent. This paper describes the VST observational strategy and the results obtained by our analysis pipelines developed to search for optical transients in multi-epoch images. We report the catalogue of the candidates with possible identifications based on light-curve fitting. We have identified two dozens of SNe, nine AGNs, and one QSO. Nineteen transients characterized by a single detection were not classified. We have restricted our analysis only to the candidates that fall into the refined localization map. None out of 39 left candidates could be positively associated with GW170814. This result implies that the possible emission of optical radiation from a BBH merger had to be fainter than r ∼ 22 (Loptical ∼ 1.4 × 1042 erg s−1) on a time interval ranging from a few hours up to two months after the gravitational wave event.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 The VOICE Survey : VST Optical Imaging of the CDFS and ES1 Fields(Proceedings of Science (PoS), 2016-01) Vaccari, M.; Covone, G.; Radovich, M.; Grado, A.; Limatola, L.; Botticella, M.T.; Cappellaro, E.; Paolillo, M.; Pignata, G.; De Cicco, D.; Falocco, S.; Marchetti, L.; Brescia, M.; S., Cavuoti; Longo, G.; Capaccioli, M.; Napolitano, N.; Schipani, P.We present the VST Optical Imaging of the CDFS and ES1 Fields (VOICE) Survey, a VST INAF Guaranteed Time program designed to provide optical coverage of two 4 deg2 cosmic windows in the Southern hemisphere. VOICE provides the first, multi-band deep optical imaging of these sky regions, thus complementing and enhancing the rich legacy of longer-wavelength surveys with VISTA, Spitzer, Herschel and ATCA available in these areas and paving the way for upcoming observations with facilities such as the LSST, MeerKAT and the SKA. VOICE exploits VST's OmegaCAM optical imaging capabilities and completes the reduction of WFI data available within the ES1 fields as part of the ESO-Spitzer Imaging Extragalactic Survey (ESIS) program providing ugri and uBVR coverage of 4 and 4 deg2 areas within the CDFS and ES1 field respectively. We present the survey's science rationale and observing strategy, the data reduction and multi-wavelength data fusion pipeline. Survey data products and their future updates will be released at http://www.mattiavaccari.net/voice/ and on CDS/VizieR.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.