Search for AGN counterparts of unidentified Fermi-LAT sources with optical polarimetry: Demonstration of the technique

Abstract

The third Fermi-LAT catalog (3FGL) presented the data of the first four years of observations from the Fermi Gamma-ray Space Telescope mission. There are 3034 sources, 1010 of which still remain unidentified. Identifying and classifying gamma-ray emitters is of high significance with regard to studying high-energy astrophysics. We demonstrate that optical polarimetry can be an advantageous and practical tool in the hunt for counterparts of the unidentified gamma-ray sources (UGSs). Using data from the RoboPol project, we validated that a significant fraction of active galactic nuclei (AGN) associated with 3FGL sources can be identified due to their high optical polarization exceeding that of the field stars. We performed an optical polarimetric survey within $3\sigma$ uncertainties of four unidentified 3FGL sources. We discovered a previously unknown extragalactic object within the positional uncertainty of 3FGL J0221.2+2518. We obtained its spectrum and measured a redshift of $z=0.0609\pm 0.0004$. Using these measurements and archival data we demonstrate that this source is a candidate counterpart for 3FGL J0221.2+2518 and most probably is a composite object: a star-forming galaxy accompanied by AGN. We conclude that polarimetry can be a powerful asset in the search for AGN candidate counterparts for unidentified Fermi sources. Future extensive polarimetric surveys at high galactic latitudes (e.g., PASIPHAE) will allow the association of a significant fraction of currently unidentified gamma-ray sources.

arXiv commentaccepted to A&A

References in corpus (31)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Planck 2015 results. XIII. Cosmological parameters
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The Host Galaxies of AGN
• Theoretical Modeling of Starburst Galaxies
• The Swift X-ray Telescope
• The Host Galaxies and Classification of Active Galactic Nuclei
• 9286 Stars: An Agglomeration of Stellar Polarization Catalogs
• Bayesian Estimation of Hardness Ratios: Modeling and Computations
• RoboPol: The optical polarization of gamma-ray--loud and gamma-ray--quiet blazars
• A Map of Dust Reddening to 4.5 kpc from Pan-STARRS1
• EXPORT: optical photometry and polarimetry of Vega-type and pre-main sequence stars
• The Gamma-Ray Blazar Content of the Northern Sky
• RoboPol: optical polarization-plane rotations and flaring activity in blazars
• The RoboPol optical polarization survey of gamma-ray - loud blazars
• Optical spectroscopic observations of gamma-ray blazars candidates I: preliminary results
• The RoboPol Pipeline and Control System
• Temporal Correlations Between Optical and Gamma-ray Activity in Blazars
• Gamma-ray Emitting Narrow Line Seyfert 1 Galaxies in The Sloan Digital Sky Survey
• Multiwavelength Cross-Correlations and Flaring Activity in Bright Blazars
• Pulsar searches of Fermi unassociated sources with the Effelsberg telescope
• Identification of the Early Fermi LAT Gamma-Ray Bright Objects with Extragalactic VLBI sources
• Blazar Flaring Patterns (B-FlaP): Classifying Blazar Candidates of Uncertain type in the third Fermi-LAT catalog by Artificial Neural Networks
• Radio-to-gamma-ray Monitoring of the Narrow-Line Seyfert 1 Galaxy PMN J0948+0022 from 2008 to 2011
• Hunting for treasures among the Fermi unassociated sources: a multi-wavelength approach
• The Gamma-ray Blazar Quest: new optical spectra, state of art and future perspectives
• Search for gamma-ray-emitting active galactic nuclei in the Fermi-LAT unassociated sample using machine learning
• Optical polarization map of the Polaris Flare with RoboPol
• 3FGLzoo. Classifying 3FGL Unassociated Fermi-LAT Gamma-ray Sources by Artificial Neural Networks
• Radio Follow-up on all Unassociated Gamma-ray Sources from the Third Fermi Large Area Telescope Source Catalog
• Pulsar Candidates Toward Fermi Unassociated Sources

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