High-energy gamma-ray sources in the VVV survey - I. The blazars

Abstract

There is a lack of blazar detections in the galactic plane area, even in the most recent blazar catalogues, mainly due to incompleteness resulting from interstellar dust and stellar contamination of our Galaxy. The VISTA Variables in the Via Láctea survey (VVV) aims to map variable sources towards the galactic plane in the near-infrared (IR). There are three catalogued and one candidate blazars in the VVV area, which are also detected by Fermi-LAT in the gamma-ray band and by the Wide-field Infrared Survey Explorer (WISE) at mid-IR wavelengths. We study the physical properties of these blazars in order to use them as a reference that would allow us to find counterparts of other unidentified gamma-ray sources in the future. All four sources have VVV counterparts, and two of them, 5BZUJ1731-3003 and 5BZQJ1802-3940 are also associated with WISE sources. They present very different properties compared with stellar or extragalactic objects. Their VVV Ks light curves show significant variability, and are characterized using a machine learning analysis. In particular, the blazar 5BZQJ1802-3940, a flat spectrum radio quasar, exhibits the smallest uncertainties in the Fermi-LAT position and it is a bright WISE source. Its near-IR properties in the colour- magnitude and colour-colour diagrams are very different from the stars and extragalactic objects in the field. It has the highest amplitude in the Ks differential light curve and fractional variability amplitude. This pilot study will allow us to search for and identify other blazars hidden behind the Galactic plane using the VVV survey data base.