Examinando por Autor "Smith, HA"

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    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, G
    Blazars, 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.
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    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, HA
    The 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.