Repositorio Institucional Académico. Universidad Andrés Bello. Chile

Examinando por Autor "Schipani, P."

Mostrando 1 - 13 de 13

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.
GRAWITA: VLT Survey Telescope observations of the gravitational wave sources GW150914 and GW151226
(Oxford University Press, 2018-02) Brocato, E.; Branchesi, M.; Cappellaro, E.; Covino, S.; Grado, A.; Greco, G.; Limatola, L.; Stratta, G.; Yang, S.; Campana, S.; D'Avanzo, P.; Getman, F.; Melandri, A.; Nicastro, L.; Palazzi, E.; Pian, E.; Piranomonte, S.; Pulone, L.; Rossi, A.; Tomasella, L.; Amati, L.; Antonelli, L.A.; Ascenzi, S.; Benetti, S.; Bulgarelli, A.; Capaccioli, M.; Cella, G.; Dadina, M.; De Cesare, G.; D'Elia, V.; Ghirlanda, G.; Ghisellini, G.; Giuffrida, G.; Iannicola, G.; Israel, G.; Lisi, M.; Longo, F.; Mapelli, M.; Marinoni, S.; Marrese, P.; Masetti, N.; Patricelli, B.; Possenti, A.; Radovich, M.; Razzano, M.; Salvaterra, R.; Schipani, P.; Spera, M.; Stamerra, A.; Stella, L.; Tagliaferri, G.; Testa, V.
We report the results of deep optical follow-up surveys of the first two gravitational-wave sources, GW150914 and GW151226, done by the GRAvitationalWave Inaf TeAm Collaboration (GRAWITA). The VLT Survey Telescope (VST) responded promptly to the gravitational wave alerts sent by the LIGO and Virgo Collaborations, monitoring a region of 90 and 72 deg 2 for GW150914 and GW151226, respectively, and repeated the observations over nearly two months. Both surveys reached an average limiting magnitude of about 21 in the r band. The paper describes the VST observational strategy and two independent procedures developed to search for transient counterpart candidates in multi-epoch VST images. Several transients have been discovered but no candidates are recognized to be related to the gravitational wave events. Interestingly, among many contaminant supernovae, we find a possible correlation between the supernova VSTJ57.77559-59.13990 and GRB150827A detected by Fermi-GBM. The detection efficiency of VST observations for different types of electromagnetic counterparts of gravitational wave events is evaluated for the present and future follow-up surveys. © 2017 The Author(s).
SOXS control electronics design
(SPIE, 2018-06) Capasso, G.; Colapietro, M.; D'Orsi, S.; Schipani, P.; Aliverti, M.; Kuncarayakti, H.; Scuderi, S.; Coretti, I.; Campana, S.; Claudi, R.; Baruffolo, A.; Ben-Ami, S.; Biondi, F.; Brucalassi, A.; Cosentino, R.; D'Alessio, F.; D'Avanzo, P.; Hershko, O.; Munari, M.; Rubin, A.; Vitali, F.; Achrén, J.; Araiza-Duran, J. Antonio; Arcavi, I.; Bianco, A.; Cappellaro, E.; Della Valle, M.; Diner, O.; Fantinel, D.; Fynbo, J.; Gal-Yam, A.; Genoni, M.; Hirvonen, M.; Kotilainen, J.; Kumar, T.; Landoni, M.; Lehti, J.; Li Causi, G.; Marafatto, L.; Mattila, S.; Pariani, G.; Pignata, G.; Rappaport, M.; Ricci, D.; Riva, M.; Salasnich, B.; Zanmar Sanchez, R.; Smartt, S.; Turatto, M.
SOXS (Son Of X-Shooter) is a unique spectroscopic facility that will operate at the ESO New Technology Telescope (NTT) in La Silla from 2021 onward. The spectrograph will be able to cover simultaneously the UV-VIS and NIR bands exploiting two different arms and a Common Path feeding system. We present the design of the SOXS instrument control electronics. The electronics controls all the movements, alarms, cabinet temperatures, and electric interlocks of the instrument. We describe the main design concept. We decided to follow the ESO electronic design guidelines to minimize project time and risks and to simplify system maintenance. The design envisages Commercial Off-The-Shelf (COTS) industrial components (e.g. Beckhoff PLC and EtherCAT fieldbus modules) to obtain a modular design and to increase the overall reliability and maintainability. Preassembled industrial motorized stages are adopted allowing for high precision assembly standards and a high reliability. The electronics is kept off-board whenever possible to reduce thermal issues and instrument weight and to increase the accessibility for maintenance purpose. The instrument project went through the Preliminary Design Review in 2017 and is currently in Final Design Phase (with FDR in July 2018). This paper outlines the status of the work and is part of a series of contributions describing the SO
SOXS: A wide band spectrograph to follow up transients
(SPIE, 2018-06) Schipani, P.; Campana, S.; Claudi, R.; Käufl, H.U.; Accardo, M.; Aliverti, M.; Baruffolo, A.; Ben Ami, S.; Biondi, F.; Brucalassi, A.; Capasso, G.; Cosentino, R.; D'Alessio, F.; D'Avanzo, P.; Hershko, O.; Gardiol, D.; Kuncarayacti, H.; Munari, M.; Rubin, A.; Scuderi, S.; Vitali, F.; Achrén, J.; Araiza-Duran, J. Antonio; Arcavi, I.; Bianco, A.; Cappellaro, E.; Colapietro, M.; Della Valle, M.; Diner, O.; D'Orsi, S.; Fantinel, D.; Fynbo, J.; Gal-Yam, A.; Genoni, M.; Hirvonen, M.; Kotilainen, J.; Kumar, T.; Landoni, M.; Lehti, J.; Li Causi, G.; Loreggia, D.; Marafatto, L.; Mattila, S.; Pariani, G.; Pignata, G.; Rappaport, M.; Ricci, D.; Riva, M.; Salasnich, B.; Zanmar Sanchez, R.; Smartt, S.; Turatto, M.
SOXS (Son Of X-Shooter) will be a spectrograph for the ESO NTT telescope capable to cover the optical and NIR bands, based on the heritage of the X-Shooter at the ESO-VLT. SOXS will be built and run by an international consortium, carrying out rapid and longer term Target of Opportunity requests on a variety of astronomical objects. SOXS will observe all kind of transient and variable sources from different surveys. These will be a mixture of fast alerts (e.g. gamma-ray bursts, gravitational waves, neutrino events), mid-term alerts (e.g. supernovae, X-ray transients), fixed time events (e.g. close-by passage of minor bodies). While the focus is on transients and variables, still there is a wide range of other astrophysical targets and science topics that will benefit from SOXS. The design foresees a spectrograph with a Resolution-Slit product ∼ 4500, capable of simultaneously observing over the entire band the complete spectral range from the U- to the H-band. The limiting magnitude of R∼20 (1 hr at S/N∼10) is suited to study transients identified from on-going imaging surveys. Light imaging capabilities in the optical band (grizy) are also envisaged to allow for multi-band photometry of the faintest transients. This paper outlines the status of the project, now in Final Design Phase. © 2018 SPIE.
Spectroscopic identification of r-process nucleosynthesis in a double neutron-star merger
(Nature Publishing Group, 2017-11) Pian, E.; D'Avanzo, P.; Benetti, S.; Branchesi, M.; Brocato, Campana S.; Cappellaro, E.; Covino, S.; D'Elia, V.; Fynbo, J.P.U.; Getman, F.; Ghirlanda, G.; Ghisellini, G.; Grado, A.; Greco, G.; Hjorth, J.; Kouveliotou, C.; Levan, A.; Limatola, L.; Malesani, D.; Mazzali, P.A.; Melandri, A.; Møller, P.; Nicastro, L.; Palazzi, E.; Piranomonte, S.; Rossi, A.; Salafia, O.S.; Selsing, J.; Stratta, G.; Tanaka, M.; Tanvir, N.R.; Tomasella, L.; Watson, D.; Yang, S.; Amati, L.; Antonelli, L.A.; Ascenzi, S.; Bernardini, M.G.; Boër, M.; Bufano, F.; Bulgarelli, A.; Capaccioli, M.; Casella, P.; Castro-Tirado, A.J.; Chassande-Mottin, E.; Ciolfi, R.; Copperwheat, C.M.; Dadina, M.; De Cesare, G.; Di Paola, A.; Fan, Y.Z.; Gendre, B.; Giuffrida, G.; Giunta, A.; Hunt, L.K.; Israel, G.L.; Jin, Z.-P.; Kasliwal, M.M.; Klose, S.; Lisi, M.; Longo, F.; Maiorano, E.; Mapelli, M.; Masetti, N.; Nava, L.; Patricelli, B.; Perley, D.; Pescalli, A.; Piran, T.; Possenti, A.; Pulone, L.; Razzano, M.; Salvaterra, R.; Schipani, P.; Spera, M.; Stamerra, A.; Stella, L.; Tagliaferri, G.; Testa, V.; Troja, E.; Turatto, M.; Vergani, S.D.; Vergani, D.
The merger of two neutron stars is predicted to give rise to three major detectable phenomena: a short burst of γ-rays, a gravitational-wave signal, and a transient optical-near-infrared source powered by the synthesis of large amounts of very heavy elements via rapid neutron capture (the r-process)1-3. Such transients, named 'macronovae' or 'kilonovae'4-7, are believed to be centres of production of rare elements such as gold and platinum8. The most compelling evidence so far for a kilonova was a very faint near-infrared rebrightening in the afterglow of a short γ-ray burst9,10 at redshift z = 0.356, although findings indicating bluer events have been reported11. Here we report the spectral identification and describe the physical properties of a bright kilonova associated with the gravitational-wave source12 GW170817 and γ-ray burst13,14 GRB 170817A associated with a galaxy at a distance of 40 megaparsecs from Earth. Using a series of spectra from ground-based observatories covering the wavelength range from the ultraviolet to the near-infrared, we find that the kilonova is characterized by rapidly expanding ejecta with spectral features similar to those predicted by current models15,16. The ejecta is optically thick early on, with a velocity of about 0.2 times light speed, and reaches a radius of about 50 astronomical units in only 1.5 days. As the ejecta expands, broad absorption-like lines appear on the spectral continuum, indicating atomic species produced by nucleosynthesis that occurs in the post-merger fast-moving dynamical ejecta and in two slower (0.05 times light speed) wind regions. Comparison with spectral models suggests that the merger ejected 0.03 to 0.05 solar masses of material, including high-opacity lanthanides. © 2017 Macmillan Publishers Limited, part of Springer Nature.
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.
The acquisition camera system for SOXS at NTT
(SPIE, 2018-06) Brucalassi, A.; Araiza-Durán, J.A.; Pignata, G.; Campana, S.; Claudi, R.; Schipani, P.; Aliverti, M.; Baruffolo, A.; Ben-Ami, S.; Biondi, F.; Capasso, G.; Cosentino, R.; D'Alessio, F.; D'Avanzo, P.; Gardiol, D.; Hershko, O.; Kuncarayakti, H.; Munari, M.; Ricci, D.; Riva, M.; Rubin, A.; Zanmar Sanchez, R.; Scuderi, S.; Vitali, F.; Achrén, J.; Arcavi, I.; Bianco, A.; Cappellaro, E.; Colapietro, M.; Della Valle, M.; Diner, O.; D'Orsi, S.; Fantinel, D.; Fynbo, J.; Gal-Yam, A.; Genoni, M.; Hirvonen, M.; Kotilainen, J.; Kumar, T.; Landoni, M.; Lehti, J.; Li Causi, G.; Loreggia, D.; Marafatto, L.; Mattila, S.; Pariani, G.; Rappaport, M.; Salasnich, B.; Smartt, S.; Turatto, M.
SOXS (Son of X-Shooter) will be the new medium resolution (R∼4500 for a 1 arcsec slit), high-efficiency, wide band spectrograph for the ESO-NTT telescope on La Silla. It will be able to cover simultaneously optical and NIR bands (350-2000nm) using two different arms and a pre-slit Common Path feeding system. SOXS will provide an unique facility to follow up any kind of transient event with the best possible response time in addition to high efficiency and availability. Furthermore, a Calibration Unit and an Acquisition Camera System with all the necessary relay optics will be connected to the Common Path sub-system. The Acquisition Camera, working in optical regime, will be primarily focused on target acquisition and secondary guiding, but will also provide an imaging mode for scientific photometry. In this work we give an overview of the Acquisition Camera System for SOXS with all the different functionalities. The optical and mechanical design of the system are also presented together with the preliminary performances in terms of optical quality, throughput, magnitude limits and photometric properties. © 2018 SPIE.
The assembly integration and test activities for the new SOXS instrument at NTT
(SPIE, 2018-06) Biondi, F.; Claudi, R.; Marafatto, L.; Farinato, J.; Magrin, D.; Ragazzoni, R.; Campana, S.; Schipani, P.; Aliverti, M.; Baruffolo, A.; Ben-Ami, S.; Brucalassi, A.; Capasso, G.; Cosentino, R.; D'Alessio, F.; D'Avanzo, P.; Hershko, O.; Kuncarayakti H, .; Munari, M.; Rubin, A.; Scuderi, S.; Vitali, F.; Achrén, J.; Araiza-Durán, J. Antonio; Arcavi, I.; Bianco, A.; Cappellaro, E.; Colapietro, M.; Della Valle, M.; Diner, O.; D'Orsi, S.; Fantinel, D.; Fynbo, J.; Gal-Yam, A.; Genoni, M.; Hirvonen, M.; Kotilainen, J.; Kumar, T.; Landoni, M.; Lehti, J.; Li Causi, G.; Mattila, S.; Pariani, G.; Pignata, G.; Rappaport, M.; Riva, M.; Ricci, D.; Salasnich, B.; Zanmar Sanchez, R.; Smartt, S.; Turatto, M.
Son Of X-Shooter (SOXS) is the new instrument for the ESO 3.5 m New Technology Telescope (NTT) in La Silla site (Chile) devised for the spectroscopic follow-up of transient sources. SOXS is composed by two medium resolution spectrographs able to cover the 350-2000 nm interval. An Acquisition Camera will provide a light imaging capability in the visible band. We present the procedure foreseen for the Assembly, Integration and Test activities (AIT) of SOXS that will be carried out at sub-systems level at various consortium partner premises and at system level both in Europe and Chile. © 2018 SPIE.
The common path of SOXS (Son of X-Shooter)
(SPIE, 2018-06) Claudi, R.; Aliverti, M.; Biondi, F.; Munari, M.; Zanmar Sanchez, R.; Campana, S.; Schipani, P.; Baruffolo, A.; Ben-Ami, S.; Brucalassi, A.; Capasso, G.; Cosentino, R.; D'Alessio, F.; D'Avanzo, P.; Hershko, O.; Kuncarayakti, H.; Rubin, A.; Scuderi, S.; Vitali, F.; Achrén, J.; Araiza-Durán, J.A.; Arcavi, I.; Bianco, A.; Cappellaro, E.; Colapietro, M.; Della Valle, M.; Diner, O.; D'Orsi, S.; Fantinel, D.; Fynbo, J.; Gal-Yam, A.; Genoni, M.; Hirvonen, M.; Kotilainen, J.; Kumar, T.; Landoni, M.; Lehti, J.; Li Causi, G.; Marafatto, L.; Mattila, S.; Pariani, G.; Pignata, G.; Rappaport, M.; Ricci, D.; Riva, M.; Salasnich, B.; Smartt, S.; Turatto, M.
Son of X-Shooter (SOXS) will be a high-efficiency spectrograph with a mean Resolution-Slit product of 4500 (goal 5000) over the entire band capable of simultaneously observing the complete spectral range 350-2000 nm. It consists of three scientific arms (the UV-VIS Spectrograph, the NIR Spectrograph and the Acquisition Camera) connected by the Common Path system to the NTT and the Calibration Unit. The Common Path is the backbone of the instrument and the interface to the NTT Nasmyth focus flange. The light coming from the focus of the telescope is split by the common path optics into the two different optical paths in order to feed the two spectrographs and the acquisition camera. The instrument project went through the Preliminary Design Review in 2017 and is currently in Final Design Phase (with FDR in July 2018). This paper outlines the status of the Common Path system and is accompanied by a series of contributions describing the SOXS design and properties after the instrument Preliminary Design Review. © 2018 SPIE.
The mechanical design of SOXS for the NTT
(SPIE, 2018-06) Aliverti, M.; Hershko, O.; Diner, O.; Brucalassi, A.; Pignata, G.; Kuncarayakti, H.; Bianco, A.; Campana, S.; Claudi, R.; Schipani, P.; Baruffolo, A.; Ben-Ami, S.; Biondi, F.; Capasso, G.; Cosentino, R.; D'Alessio, F.; D'Avanzo, P.; Munari, M.; Rubin, A.; Scuderi, S.; Vitali, F.; Achrén, J.; Araiza-Duran, J.A.; Arcavi, I.; Cappellaro, E.; Colapietro, M.; Della Valle, M.; D'Orsi, S.; Fantinel, D.; Fynbo, J.; Gal-Yam, A.; Genoni, M.; Hirvonen, M.; Kotilainen, J.; Kumar, T.; Landoni, M.; Lehti, J.; Li Causi, G.; Marafatto, L.; Mattila, S.; Pariani, G.; Rappaport, M.; Ricci, D.; Riva, M.; Salasnich, B.; Smartt, S.; Turatto, M.; Zanmar Sanchez, R.
SOXS (Son of X-shooter) is a wide band, medium resolution spectrograph for the ESO NTT with a first light expected in early 2021. The instrument will be composed by five semi-independent subsystems: a pre-slit Common Path (CP), an Acquisition Camera (AC), a Calibration Unit (CU), the NIR spectrograph, and the UV-VIS spectrograph. In this paper, we present the mechanical design of the subsystems, the kinematic mounts developed to simplify the final integration procedure and the maintenance. The concept of the CP and NIR optomechanical mounts developed for a simple pre- alignment procedure and for the thermal compensation of reflective and refractive elements will be shown. © 2018 SPIE.
The new SOXS instrument for the ESO NTT
(SPIE, 2016-06) Schipani, P.; Claudi, R.; Campana, S.; Baruffolo, A.; Basa, S.; Basso, S.; Cappellaro, E.; Cascone, E.; Cosentino, R.; D'Alessio, F.; De Caprio, V.; Della Valle, M.a De Ugarte Postigo A.; D'Orsi, S.; Franzen, R.; Fynbo, J.; Gal-Yam, A.; Gardiol, D.; Giro, E.; Hamuy, M.; Iuzzolino, M.; Loreggia, D.; Mattila, S.; Munari, M.; Pignata, G.; Riva, M.; Savarese, S.; Schmidt, B.; Scuderi, S.; Smartt, S.; Vitali, F.
SOXS (Son Of X-Shooter) will be a unique spectroscopic facility for the ESO-NTT 3.5-m telescope in La Silla (Chile), able to cover the optical/NIR band (350-1750 nm). The design foresees a high-efficiency spectrograph with a resolutionslit product of ∼4,500, capable of simultaneously observing the complete spectral range 350 - 1750 nm with a good sensitivity, with light imaging capabilities in the visible band. This paper outlines the status of the project. © 2016 SPIE.
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.
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.

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