Unidentified gamma-Ray Sources Hunting gamma-Ray Blazars

One of the main scientific objectives of the ongoing Fermi mission is unveiling the nature of unidentified gamma-ray sources (UGSs). Despite the major improvements of Fermi in the localization of gamma-ray sources with respect to the past gamma-ray missions, about one-third of the Fermi-detected objects are still not associated with low-energy counterparts. Recently, using the Wide-field Infrared Survey Explorer survey, we discovered that blazars, the rarest class of active galactic nuclei and the largest population of gamma-ray sources, can be recognized and separated from other extragalactic sources on the basis of their infrared (IR) colors. Based on this result, we designed an association method for the gamma-ray sources to recognize if there is a blazar candidate within the positional uncertainty region of a generic gamma-ray source. With this new IR diagnostic tool, we searched for gamma-ray blazar candidates associated with the UGS sample of the second Fermi gamma-ray LAT catalog (2FGL). We found that our method associates at least one gamma-ray blazar candidate as a counterpart to each of 156 out of 313 UGSs analyzed. These new low-energy candidates have the same IR properties as the blazars associated with gamma-ray sources in the 2FGL catalog.