Browsing by Author "Bazzano, A."

Now showing 1 - 5 of 5
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    Accurate classification of 75 counterparts of objects detected in the 54-month Palermo Swift/BAT hard X-ray catalogue
    (2014) Parisi, P.; Masetti, N.; Rojas, A. F.; Jiménez Bailón, E.; Chavushyan, V.; Palazzi, E.; Bassani, L.; Bazzano, A.; Bird, A. J.; Galaz, Gaspar; Minniti, D.; Morelli, L.; Ubertini, P.; Parisi, P.; Masetti, N.; Rojas, A. F.; Jiménez Bailón, E.; Chavushyan, V.; Palazzi, E.; Bassani, L.; Bazzano, A.; Bird, A. J.; Galaz, Gaspar; Minniti, D.; Morelli, L.; Ubertini, P.
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    BL Lacertae identifications in a ROSAT-selected sample of Fermi unidentified objects
    (2013) Masetti, N.; Sbarufatti, B.; Parisi, P.; Jimenez-Bailon, E.; Chavushyan, V.; Vogt, F. P. A.; Sguera, V.; Stephen, J. B.; Palazzi, E.; Bassani, L.; Bazzano, A.; Fiocchi, M.; Galaz, G.; Landi, R.; Malizia, A.; Minniti, D.; Morelli, L.; Ubertini, P.
    The optical spectroscopic followup of 27 sources belonging to a sample of 30 high-energy objects selected by positionally cross correlating the first Fermi/LAT Catalog and the ROSAT All-Sky Survey Bright Source Catalog is presented here. It has been found or confirmed that 25 of them are BL Lacertae objects (BL Lacs), while the remaining two are Galactic cataclysmic variables (CVs). This strongly suggests that the sources in the first group are responsible for the GeV emission detected with Fermi, while the two CVs most likely represent spurious associations. We thus find an 80% a posteriori probability that the sources selected by matching GeV and X-ray catalogs belong to the BL Lac class. We also show suggestions that the BL Lacs selected with this approach are probably high-synchrotron-peaked sources and in turn good candidates for the detection of ultra-high-energy (TeV) photons from them.
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    Searching for active galactic nuclei among unidentified INTEGRAL sources
    (2011) Maiorano, E.; Landi, R.; Stephen, J. B.; Bassani, L.; Masetti, N.; Parisi, P.; Palazzi, E.; Parma, P.; Bird, A. J.; Bazzano, A.; Ubertini, P.; Jimenez-Bailon, E.; Chavushyan, V.; Galaz, G.; Minniti, D.; Morelli, L.
    We report on a new method to identify active galactic nuclei (AGNs) among unidentified INTEGRAL sources. This method consists of cross-correlating unidentified sources listed in the fourth Imager on Board the INTEGRAL Satellite (IBIS) Survey Catalogue first with infrared and then with radio catalogues and a posteriori verifying, by means of X-ray and optical follow-up observations, the likelihood of these associations. In order to test this method, a sample of eight sources has been extracted from the fourth IBIS catalogue. For seven sources of the sample, we obtained an identification, whereas the last one (IGR J03103+5706) has insufficient information for a clear classification and deserves more in-depth study. We identified three objects (IGR J08190-3835, IGR J17520-6018 and IGR J21441+4640) as AGNs and suggest that three more (IGR J00556+7708, IGRJ17219-1509 and IGR J21268+6203) are likely active galaxies on the basis of their radio spectra, near-infrared photometry and location above the Galaxy plane. One source (IGR J05583-1257) has been classified as a starburst galaxy, but it might have been spuriously associated with the INTEGRAL detection.
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    The agn nature of 11 out of 12 SWIFT/RXTE unidentified sources through optical and X-ray spectroscopy
    (2007) Landi, R.; Masetti, N.; Morelli, L.; Palazzi, E.; Bassani, L.; Malizia, A.; Bazzano, A.; Bird, A. J.; Dean, A. J.; Galaz, G.; Minniti, D.; Ubertini, P.
    The Swift Burst Alert Telescope (BAT) is performing a high Galactic latitude survey in the 14-195 keV band at a flux limit of similar to 10(-11) ergs cm(-2) s(-1), leading to the discovery of new high-energy sources, most of which have not yet been properly classified. A similar work has also been performed with the RXTE slew survey, leading to the discovery of 68 sources detected above 8 keV, many of which are still unclassified. Follow-up observations with the Swift X-ray Telescope (XRT) provide, for many of these objects, source localization with a positional accuracy of a few arcseconds, thus allowing the search for optical counterparts to be more efficient and reliable. We present the results of optical/X-ray follow-up studies of 11 Swift BAT detections and one AGN detected in the RXTE Slew Survey, aimed at identifying their longer wavelength counterparts and at assessing their nature. These data allowed, for the first time, the optical classification of eight objects and a distance determination for three of them. For another object, a more refined optical classification than that available in the literature is also provided. For the remaining sources, optical spectroscopy provides a characterization of the source near in time to the X-ray measurement. The sample consists of six Seyfert 2 galaxies, five Seyferts of intermediate type 1.2-1.8, and one object of Galactic nature -an intermediate polar (i.e., magnetic) cataclysmic variable. Out of the 11 AGNs, 8 (similar to 70%), including 2 Seyferts of type 1.2 and 1.5, are absorbed with N-H > 10(22) cm(-2). Up to 3 objects could be Compton thick (i.e., N-H > 1.5 x 10(24) cm(-2)), but only in one case (Swift J0609.1-8636) does all the observational evidence strongly suggest this possibility. The present data demonstrate the capability of coordinated hard X-ray and optical observations to discover absorbed AGNs.
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    The nature of 50 Palermo Swift-BAT hard X-ray objects through optical spectroscopy
    (2017) Rojas, A. F.; Masetti, N.; Minniti, D.; Jiménez Bailón, E.; Chavushyan, V.; Hau, G.; McBride, V. A.; Bassani, L.; Bazzano, A.; Galaz, Gaspar; Rojas, A. F.; Masetti, N.; Minniti, D.; Jiménez Bailón, E.; Chavushyan, V.; Hau, G.; McBride, V. A.; Bassani, L.; Bazzano, A.; Galaz, Gaspar