Abstract

One of the unsolved mysteries of gamma-ray astronomy concerns the nature of the unidentified gamma-ray sources. Here I report on 2FGL J1823.8+4312, a gamma-ray active galactic nucleus of uncertain type associated with the X-ray source 1RXS J182418.7+430954 according to the 2FGL, to verify whether if it is a blazar. Applying the association method based on the WISE archive and the Second Fermi LAT source catalog I found two sources with IR colors typical of gamma-ray blazars, located within 99.9% confidence region of the location of 2FGL J1823.8+4312: WISE J182352.33+431452.5 and WISE J182409.25+431404.7.

Then, searching in the Chandra, NVSS and SDSS archival observations for their counterparts, I discovered that WISE J182352.33+431452.5, the preferred gamma-ray blazar candidate according to the WISE association procedure, is detected in the optical and in the X-rays but not in the radio, making it extremely unusual if it is a blazar. Given its enigmatic spectral energy distribution, I consider the possibility that it is a "radio faint blazar" or the prototype of a new class of extragalactic sources, independent of whether WISE J182352.33+431452.5 is the actual counterpart of 2FGL J1823.8+4312.