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Title: UNVEILING THE NATURE OF THE UNIDENTIFIED GAMMA-RAY SOURCES. IV. THE SWIFT CATALOG OF POTENTIAL X-RAY COUNTERPARTS

A significant fraction (∼30%) of the high-energy γ-ray sources listed in the second Fermi Large Area Telescope (LAT) catalog are still of unknown origin, having not yet been associated with counterparts at lower energies. To investigate the nature of these enigmatic sources, we present an extensive search of X-ray sources lying in the positional uncertainty region of a selected sample of these unidentified gamma-ray sources (UGSs) that makes use of all available observations performed by the Swift X-ray Telescope before 2013 March 31, available for 205 UGSs. To detect the fainter sources, we merged all the observations covering the Fermi LAT positional uncertainty region at a 95% level of confidence of each UGS. This yields a catalog of 357 X-ray sources, finding candidate X-ray counterparts for ∼70% of the selected sample. In particular, 25% of the UGSs feature a single X-ray source within their positional uncertainty region, while 45% have multiple X-ray sources. For each X-ray source, we also looked in the corresponding Swift UVOT merged images for optical and ultraviolet counterparts, also performing source photometry. We found ultraviolet-optical correspondences for ∼70% of the X-ray sources. We searched several major radio, infrared, optical, and ultraviolet surveys for possible counterparts withinmore » the positional error of the sources in the X-ray catalog to obtain additional information on their nature. Applying the kernel density estimation technique to infrared colors of Wide-Field Infrared Survey Explorer counterparts of our X-ray sources we select six γ-ray blazar candidates. In addition, comparing our results with previous analyses, we select 11 additional γ-ray blazar candidates.« less
Authors:
; ;  [1] ; ;  [2] ;  [3] ;  [4] ;  [5]
  1. Harvard-Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)
  2. SLAC National Laboratory and Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States)
  3. INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, I-40129 Bologna (Italy)
  4. INAF Istituto di Radioastronomia, via Gobetti 101, I-40129 Bologna (Italy)
  5. Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia (Italy)
Publication Date:
OSTI Identifier:
22273273
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal, Supplement Series; Journal Volume: 209; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; CATALOGS; COLOR; COMPARATIVE EVALUATIONS; COSMIC GAMMA SOURCES; DENSITY; GAMMA ASTRONOMY; INFRARED SURVEYS; PHOTOMETRY; QUASARS; TELESCOPES; ULTRAVIOLET RADIATION; X-RAY GALAXIES