Examinando por Autor "Chavushyan, Vahram"

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    Optical Spectroscopic Observations of Gamma-Ray Blazar Candidates. XII. Follow-up Observations from SOAR, Blanco, NTT, and OAN-SPM
    (American Astronomical Society, 2023-03) García-Pérez, Abigail; Peña-Herazo, Harold A.; Massaro, Francesco; Chavushyan, Vahram; D’abrusco, Raffaele; Masetti, Nicola; Landoni, Marco; Franca, Fabio La; Patiño-Álvarez, Víctor M.; Amaya-Almazán, Raúl A.; Milisavljevic, Dan; Paggi, Alessandro; Ricci, Federica; Jiménez-Bailón, Elena; Smith, Howard A.
    Roughly one third of the sources in the Fermi-LAT catalogs are listed as unidentified/unassociated γ-ray sources (UGS), i.e., they lack a low-energy counterpart. In addition, there is a growing population of blazars of uncertain type (BCUs). Spectroscopic observations are crucial to confirm the blazar nature of the UGSs candidate counterparts and BCUs. Hence, in 2013 we started an optical spectroscopic campaign to carry out the identifications and classifications. In this paper, as a continuation of the campaign we report the spectra of 39 sources: the sample comprises 37 sources classified as BCUs, one source classified as a BL Lac in the Fourth Source Catalog of the Fermi-LAT (4FGL), and one source classified as UGS. We classify 19 of the sources in the sample as BL Lacs, 13 as blazars with nonnegligible host-galaxy emission, six as Flat Spectrum Radio Quasars, and one as a normal elliptical galaxy. The source listed as BL Lac in the 4FGL seems to be a blazar with nonnegligible host-galaxy emission in our observations, most likely due to an ongoing quiescent state. We classified the UGS source as a BL Lac. Six out of the 39 sources were previously reported in the campaign; in general, both the classifications and redshifts are in agreement, except for one of them with no redshift reported before. Altogether, we provided reliable redshift estimates to 21 out of the 39 sources. Finally, we describe the statistics of the data collected in our campaign so far. © 2023. The Author(s). Published by the American Astronomical Society.
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    Two New Catalogs of Blazar Candidates in the WISE Infrared Sky
    (Astrophysical Journal, Supplement Series, 2019) D’Abrusco, Raffaele; Álvarez Crespo, Nuria; Massaro, Francesco; Campana, Riccardo; Chavushyan, Vahram; Landoni, Marco; La Franca, Fabio; Masetti, Nicola; Milisavljevic, Dan; Paggi, Alessandro; Ricci, Federica; Smith, Howard A.
    We present two catalogs of radio-loud candidate blazars whose Wide-Field Infrared Survey Explorer (WISE) mid-infrared colors are selected to be consistent with the colors of confirmed γ-ray-emitting blazars. The first catalog is the improved and expanded release of the WISE Blazar-like Radio-Loud Sources (WIBRaLS) catalog presented by D’Abrusco et al. It includes sources detected in all four WISE filters, spatially cross-matched with radio sources in one of three radio surveys and radio-loud based on their q22 spectral parameter. WIBRaLS2 includes 9541 sources classified as BL Lacs, flat-spectrum radio quasars, or mixed candidates based on their WISE colors. The second catalog, called KDEBLLACS, based on a new selection technique, contains 5579 candidate BL Lacs extracted from the population of WISE sources detected in the first three WISE passbands ([3.4], [4.6], and [12]) only, whose mid-infrared colors are similar to those of confirmed, γ-ray BL Lacs. Members of KDBLLACS are also required to have a radio counterpart and be radio-loud based on the parameter q12, defined similarly to the q22 used for the WIBRaLS2. We describe the properties of these catalogs and compare them with the largest samples of confirmed and candidate blazars in the literature. We cross-match the two new catalogs with the most recent catalogs of γ-ray sources detected by the Fermi Large Area Telescope. Since spectroscopic observations of candidate blazars from the first WIBRaLS catalog within the uncertainty regions of γ-ray unassociated sources confirmed that ∼90% of these candidates are blazars, we anticipate that these new catalogs will again play an important role in the identification of the γ-ray sky.