Searching for gamma-ray blazar candidates among the unidentified INTEGRAL sources

Abstract

The identification of low-energy counterparts for gamma-ray sources is one of the biggest challenge in modern gamma-ray astronomy. Recently, we developed and successfully applied a new association method to recognize gamma-ray blazar candidates that could be possible counterparts for the unidentified gamma-ray sources above 100 MeV in the second Fermi Large Area Telescope (LAT) catalog (2FGL). This method is based on the Infrared (IR) colors of the recent Wide-Field Infrared Survey Explorer (WISE) all-sky survey. In this letter we applied our new association method to the case of unidentified INTEGRAL sources (UISs) listed in the fourth soft gamma-ray source catalog (4IC). Only 86 UISs out of the 113 can be analyzed, due to the sky coverage of the WISE Preliminary data release. Among these 86 UISs, we found that 18 appear to have a gamma-ray blazar candidate within their positional error region. Finally, we analyzed the SWIFT archival data available for 10 out these 18 gamma-ray blazar candidates, and we found that 7 out of 10 are clearly detected in soft X-rays and/or in the optical-ultraviolet band. We cannot confirm the associations between the UISs and the selected gamma-ray blazar candidates due to the discrepancies between the INTEGRAL and the soft X-ray spectra. However, the discovery of the soft X-ray counterparts for the selected gamma-ray blazar candidates adds an important clue to help understand their origin and to confirm their blazar nature.

13 pages, 4 figures, 1 table, accepted for publication on the Astrophysical Journal Letters

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Cited by in corpus (15)

• The 105 month Swift-BAT all-sky hard X-ray survey
• Unveiling the nature of the unidentified gamma-ray sources I: a new method for the association of gamma-ray blazars
• Unveiling the nature of the unidentified gamma-ray sources II: radio, infrared and optical counterparts of the gamma-ray blazar candidates
• Optical spectroscopic observations of gamma-ray blazar candidates II. The 2013 KPNO campaign in the Northern Hemisphere
• Optical Spectroscopic Observations of Gamma-ray Blazar Candidates. V. TNG, KPNO, and OAN Observations of Blazar Candidates of Uncertain Type in the Northern Hemisphere
• Optical spectroscopic observations of gamma-ray blazar candidates III. The 2013/2014 campaign in the Southern Hemisphere
• Optical spectroscopic observations of gamma-ray blazar candidates IV. Results of the 2014 follow-up campaign
• Refining the associations of the Fermi Large Area Telescope Source Catalogs
• Basic properties of Fermi blazars and the "blazar sequence"
• Localizing INTEGRAL Sources with Chandra: X-Ray and Multi-Wavelength Identifications and Energy Spectra
• Identification of New Gamma-Ray Blazar Candidates With Multifrequency Archival Observations
• Searching for new gamma-ray blazar candidates in the 3rd Palermo BAT Hard X-ray Catalog with WISE
• Chandra Observations of High Energy X-ray Sources Discovered by INTEGRAL
• Quasi-star jets as unidentified gamma-ray sources
• Source identification for the Swift-BAT 150-month hard X-ray catalog using soft X-ray observations