Fermi Large Area Telescope Observations of a Candidate Young Radio Source

Using 19 months of Fermi LAT data, we investigate the gamma-ray properties of the radio-loud active galaxy 4C+55.17 (z=0.896) and re-examine its classification as a quasar-hosted blazar, considering instead its possible nature as a gamma-ray emitting young radio source. The active galaxy 4C+55.17 has a history of gamma-ray observations dating back to the EGRET era. Commonly classified as a Flat Spectrum Radio Quasar (FSRQ) due to its radio spectral shape and broad optical emission lines, the association of the EGRET source with 4C+55.17 remained tentative at the time, as the source exhibited spectral and morphological properties that were unlike any of the other bright gamma-ray blazars. With the improved angular resolution and sensitivity of the Large Area Telescope on board the Fermi Gamma-ray Space Telescope, the association of the gamma-ray source with 4C+55.17 is now confirmed due to the precise gamma-ray localization. An investigation of the gamma-ray properties of this source has revealed it to be an atypical member of the gamma-ray emitting FSRQ's, with an unusually hard and non-variable gamma-ray spectrum which extends up to the observed photon energies of 145 GeV despite its considerably high redshift for a very-high energy (>100 GeV) emitter. We further show that the high energy (>100 MeV) spectrum of this source may be formally extrapolated into the detectable range of ground-based Cherenkov telescopes, making it a compelling candidate for very-high energy observations, and in particular for future studies of the extragalactic background light.