The WISE gamma-ray strip parametrization: the nature of the gamma-ray Active Galactic Nuclei of Uncertain type

TL;DR

This paper introduces a new IR color-based parameterization of the WISE Gamma-ray Strip to identify blazar candidates among uncertain gamma-ray sources, significantly improving source classification accuracy.

Contribution

The study develops a single-parameter method to determine if gamma-ray AGNs of uncertain type align with the WISE Gamma-ray Strip, aiding in blazar identification.

Findings

Approximately 90% of analyzed AGUs are consistent with the WISE Gamma-ray Strip.

The proposed IR color parameter effectively distinguishes blazar candidates.

Most AGUs can be classified as blazar candidates using IR color criteria.

Abstract

Despite the large number of discoveries made recently by Fermi, the origins of the so called unidentified gamma-ray sources remain unknown. The large number of these sources suggests that among them there could be a population that significantly contributes to the isotropic gamma-ray background and is therefore crucial to understand their nature. The first step toward a complete comprehension of the unidentified gamma-ray source population is to identify those that can be associated with blazars, the most numerous class of extragalactic sources in the gamma-ray sky. Recently, we discovered that blazars can be recognized and separated from other extragalactic sources using the infrared (IR) WISE satellite colors. The blazar population delineates a remarkable and distinctive region of the IR color-color space, the WISE blazar strip. In particular, the subregion delineated by the gamma-ray emitting blazars is even narrower and we named it as the WISE Gamma-ray Strip (WGS). In this paper we parametrize the WGS on the basis of a single parameter s that we then use to determine if gamma-ray Active Galactic Nuclei of the uncertain type (AGUs) detected by Fermi are consistent with the WGS and so can be considered blazar candidates. We find that 54 AGUs out of a set 60 analyzed have IR colors consistent with the WGS; only 6 AGUs are outliers. This result implies that a very high percentage (i.e., in this sample about 90%) of the AGUs detected by Fermi are indeed blazar candidates.