Swift/XRT counterparts to unassociated Fermi high-energy LAT sources

Abstract

We report the results from our analysis of a large set of archival data acquired with the X-ray telescope (XRT) onboard Swift, covering the sky region surrounding objects from the first Fermi Large Area Telescope (LAT) catalogue of high-energy sources (1FHL), which still lack an association. Of the 23 regions analysed, ten did not show any evidence of X-ray emission, but 13 were characterised by the presence of one or more objects emitting in the 0.3-10 keV band. Only in a couple of cases is the X-ray counterpart located outside the Fermi positional uncertainty, while in all other cases the associations found are compatible with the high-energy error ellipses. All counterparts we found have been studied in detail by means of a multi-waveband approach to evaluate their nature or class; in most cases, we have been able to propose a likely or possible association except for one Fermi source whose nature remains doubtful at the moment. The majority of the likely associations are extragalactic in nature, most probably blazars of the BL Lac type.

13 pages, 5 figures, 4 tables. Accepted for publication in A&A

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Cited by in corpus (19)

• Fermi Large Area Telescope Fourth Source Catalog
• Optical spectroscopic survey of a sample of Unidentified Fermi objects
• Optical spectroscopic survey of a sample of Unidentified Fermi objects: II
• Optical spectroscopy of BL Lac objects: TeV candidates
• Optical spectroscopic observations of gamma-ray blazar candidates VIII: the 2016-2017 follow up campaign carried out at SPM, NOT, KPNO and SOAR telescopes
• Radio Weak BL Lac objects in the Fermi era
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• A new method to unveil blazars among multi-wavelength counterparts of Unassociated Fermi gamma-ray Sources
• Optical spectroscopic observations of gamma-ray blazar candidates. IX. Optical archival spectra and further observations from SOAR and OAGH
• Looking for blazars in a sample of unidentified high-energy emitting Fermi sources
• Swift/XRT counterparts to unassociated Fermi high-energy LAT sources
• Optical spectroscopic observations of low-energy counterparts of Fermi-LAT gamma-ray sources
• The $\gamma$-ray sky seen at X-ray energies I. Searching for the connection between X-rays and $\gamma$-rays in Fermi BL Lac objects
• VLBA observations of radio faint Fermi-LAT sources above 10 GeV
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• The loud and the quiet: searching for radio counterparts of two radio-weak BL Lac candidates with VLBI
• Search for the multiwavelength counterparts to extragalactic unassociated Fermi γ-ray sources
• Disentangling the nature of the prototype radio weak BL Lac: Contemporaneous multifrequency observations of WISE J141046.00 + 740511.2
• Exploring the nature of Galactic unassociated sources detected by the Fermi-LAT