Examinando por Autor "Masetti, N"
Mostrando 1 - 6 de 6
Resultados por página
Opciones de ordenación
Ítem BAT AGN Spectroscopic Survey – III. An observed link between AGN Eddington ratio and narrow-emission-line ratios(OXFORD UNIV PRESS, 2016-09) Oh, K; Schawinski, K; Koss, M; Trakhtenbrot, B; Lamperti, I; Ricci, C; Mushotzky, R; Veilleux, S; Berney, S; Crenshaw, DM; Gehrels, N; Harrison, F; Masetti, N; Soto, KT; Stern, D; Treister, E; Ueda, YWe investigate the observed relationship between black hole mass (M-BH), bolometric luminosity (L-bol) and Eddington ratio (lambda(Edd)) with optical emission-line ratios ([N II] lambda 6583/H alpha, [S II] lambda lambda 6716, 6731/H alpha, [O I] lambda 6300/H alpha, [O III] lambda 5007/H beta, [Ne III] lambda 3869/H beta and He II lambda 4686/H beta) of hard X-ray-selected active galactic nuclei (AGN) from the BAT AGN Spectroscopic Survey. We show that the [N II] lambda 6583/H alpha ratio exhibits a significant correlation with lambda(Edd) (R-Pear = -0.44, p-value = 3 x 10(-13), sigma = 0.28 dex), and the correlation is not solely driven by M-BH or L-bol. The observed correlation between [N II] lambda 6583/H alpha ratio and M-BH is stronger than the correlation with L-bol, but both are weaker than the lambda(Edd) correlation. This implies that the large-scale narrow lines of AGN host galaxies carry information about the accretion state of the AGN central engine. We propose that [N II] lambda 6583/H alpha is a useful indicator of Eddington ratio with 0.6 dex of rms scatter, and that it can be used to measure lambda(Edd) and thus M-BH from the measured L-bol, even for high-redshift obscured AGN. We briefly discuss possible physical mechanisms behind this correlation, such as the mass-metallicity relation, X-ray heating, and radiatively driven outflows.Ítem Looking for blazars in a sample of unidentified high-energy emitting Fermi sources(EDP SCIENCES, 2016-11) Marchesini, EJ; Masetti, N; Chavushyan, V; Cellone, SA; Andruchow, I; Bassani, L; Bazzano, A; Jimenez-Bailon, E; Landi, R; Malizia, A; Palazzi, E; Patino-Alvarez, V; Rodriguez-Castillo, GA; Stephen, JB; Ubertini, PContext. Based on their overwhelming dominance among associated Fermi gamma-ray catalogue sources, it is expected that a large fraction of the unidentified Fermi objects are blazars. Through crossmatching between the positions of unidentified gamma-ray sources from the First Fermi Catalog of gamma-ray sources emitting above 10 GeV (1FHL) and the ROSAT and Swift/XRT catalogues of X-ray objects and between pointed XRT observations, a sample of 36 potential associations was found in previous works with less than 15 arcsec of positional off set. One-third of them have recently been classified; the remainder, though believed to belong to the blazar class, still lack spectroscopic classifications. Aims. We study the optical spectrum of the putative counterparts of these unidentified gamma-ray sources in order to find their redshifts and to determine their nature and main spectral characteristics. Methods. An observational campaign was carried out on the putative counterparts of 13 1FHL sources using medium-resolution optical spectroscopy from the Osservatorio Astronomico di Bologna in Loiano, Italy; the Telescopio Nazionale Galileo and the Nordic Optical Telescope, both in the Canary Islands, Spain; and the Observatorio Astronomico Nacional San Pedro Martir in Baja California, Mexico. Results. We were able to classify 14 new objects based on their continuum shapes and spectral features. Conclusions. Twelve new blazars were found, along with one new quasar and one new narrow line Seyfert 1 (NLS1) to be potentially associated with the 1FHL sources of our sample. Redshifts or lower limits were obtained when possible alongside central black hole mass and luminosity estimates for the NLS1 and the quasar.Ítem OPTICAL SPECTROSCOPIC OBSERVATIONS OF GAMMA-RAY BLAZAR CANDIDATES. VI. FURTHER OBSERVATIONS FROM TNG, WHT, OAN, SOAR, AND MAGELLAN TELESCOPES(IOP PUBLISHING, 2016) Crespo, NA; Massaro, F; Milisavljevic, D; Landoni, M; Chavushyan, V; Patino-Alvarez, V; Masetti, N; Jimenez-Bailon, E; Strader, J; Chomiuk, L; Katagiri, H; Kagaya, M; Cheung, CC; Paggi, A; D'Abrusco, R; Ricci, F; La Franca, F; Smith, HA; Tosti, GBlazars, one of the most extreme classes of active galaxies, constitute so far the largest known population of.-ray sources, and their number is continuously growing in the Fermi catalogs. However, in the latest release of the Fermi catalog there is still a large fraction of sources that are classified as blazar candidates of uncertain type (BCUs) for which optical spectroscopic observations are necessary to confirm their nature and their associations. In addition, about one-third of the gamma-ray point sources listed in the Third Fermi-LAT Source Catalog (3FGL) are still unassociated and lacking an assigned lower-energy counterpart. Since 2012 we have been carrying out an optical spectroscopic campaign to observe blazar candidates to confirm their nature. In this paper, the sixth of the series, we present optical spectroscopic observations for 30 gamma-ray blazar candidates from different observing programs we carried out with the Telescopio Nazionale Galileo, William Herschel Telescope, Observatorio Astronomico Nacional, Southern Astrophysical Research Telescope, and Magellan. Telescopes. We found that 21 out of 30 sources investigated are BL Lac objects, while the remaining targets are classified as flat-spectrum radio quasars showing the typical broad emission lines of normal quasi-stellar objects. We conclude that our selection of gamma-ray blazar. candidates based on their multifrequency properties continues to be a successful way to discover potential low-energy counterparts of the Fermi. unidentified gamma-ray sources and to confirm the nature of BCUs.Ítem RADIO-WEAK BL LAC OBJECTS IN THE FERMI ERA(ASTROPHYSICAL JOURNAL, 834 (2):10.3847/1538-4357/834/2/113 JAN 6 201, 2017-01) Massaro, F; Marchesini, EJ; D'Abrusco, R; Masetti, N; Andruchow, I; Smith, HAThe existence of "radio-weak BL Lac objects" (RWBLs) has been an open question, and has remained unsolved since the discovery that quasars could be radio-quiet or radio-loud. Recently, several groups identified RWBL candidates, mostly found while searching for low-energy counterparts of the unidentified or. unassociated gammaray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs (WDs) or weak. emission. line quasars (WELQs) when there are not sufficient data to precisely draw their broadband spectral energy distribution, and their classification is mainly based on a featureless optical spectra. Motivated by the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs, and BL Lacs using the [3.4]-[4.6]-[12] mu m color-color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38 + 603131 and WISE J141046.00 + 740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with that. of the BL Lac population.Ítem Searching for supergiant fast X-ray transients with Swift(EDP SCIENCES, 2016-09) Romano, P; Bozzo, E; Esposito, P; Sbarufatti, B; Haberl, F; Ponti, G; D'Avanzo, P; Ducci, L; Segreto, A; Jin, C; Masetti, N; Del Santo, M; Campana, S; Mangano, VSupergiant fast X-ray transients (SFXTs) are high mass X-ray binaries (HMXBs) hosting a neutron star and an OB supergiant companion. We examine the available Swift data, as well as other new or archival / serendipitous data, on three sources: IGR J17407 2808, 2XMM J185114.3 000004, and IGR J18175 2419, whose X-ray characteristics qualify them as candidate SFXT, to explore their properties and test whether they are consistent with an SFXT nature. Since IGR J17407 2808 and 2XMM J185114.3 000004 triggered the Burst Alert Telescope on board Swift, the Swift data enable us to provide their first arcsecond localisations, leading to an unequivocal identification of the source CXOU J174042.0 280724 as the soft X-ray counterpart of IGR J17407 2808, as well as their first broadband spectra, which can be fit with models generally describing accreting neutron stars in HMXBs. While still lacking optical spectroscopy to assess the spectral type of the companion, we propose 2XMM J185114.3 000004 as a very strong SFXT candidate. The nature of IGR J17407 2808 remains, instead, more uncertain. Its broadband properties cannot exclude the fact that the emission originates from either an HMXB (and in that case, an SFXT) or, more likely, a low-mass X-ray binary. Finally, based on the deep non-detection in our XRT monitoring campaign and a careful reanalysis of the original INTEGRAL data in which the discovery of the source was first reported, we show that IGR J18175 2419 is likely a spurious detection.Ítem VVV-WIT-04: An extragalactic variable source caught by the VVV Survey(Oxford University Press, 2019-11) Saito, R K; Minniti, D; Ivanov, V D; Masetti, N; Navarro, M G; Fernandes, R Cid; Ruschel-Dutra, D; Smith, L C; Lucas, P W; Gonzalez-Fernandez, C; Contreras Ramos, RWe report the discovery of VVV-WIT-04, a near-infrared (near-IR) variable source towards the Galactic disc located ∼0.2 arcsec apart from the position of the radio source PMN J1515−5559. The object was found serendipitously in the near-IR data of the ESO public survey VISTA Variables in the Vía Láctea (VVV). Our analysis is based on variability, multicolour, and proper motion data from VVV and VVV eXtended surveys, complemented with archive data at longer wavelengths. We suggest that VVV-WIT-04 has an extragalactic origin as the near-IR counterpart of PMN J1515−5559. The Ks-band light curve of VVV-WIT-04 is highly variable and consistent with that of an optically violent variable quasar. The variability in the near-IR can be interpreted as the redshifted optical variability. Residuals to the proper motion vary with the magnitude suggesting contamination by a blended source. Alternative scenarios, including a transient event such as a nova or supernova, or even a binary microlensing event, are not in agreement with the available data. © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society