We report the \gamma -ray detection of a young radio galaxy , PKS 1718 - 649 , belonging to the class of Compact Symmetric Objects ( CSOs ) , with the Large Area Telescope ( LAT ) on board the Fermi satellite .
The third Fermi Gamma-ray LAT catalog ( 3FGL ) includes an unassociated \gamma -ray source , 3FGL J1728.0 - 6446 , located close to PKS 1718 - 649 .
Using the latest Pass 8 calibration , we confirm that the best fit 1 \sigma position of the \gamma -ray source is compatible with the radio location of PKS 1718 - 649 .
Cross-matching of the \gamma -ray source position with the positions of blazar sources from several catalogs yields negative results .
Thus , we conclude that PKS 1718 - 649 is the most likely counterpart to the unassociated LAT source .
We obtain a detection test statistics TS \sim 36 ( > 5 \sigma ) with a best fit photon spectral index \Gamma = 2.9 \pm 0.3 and a 0.1-100 GeV photon flux density F _ { 0.1 - 100 GeV } = ( 11.5 \pm 0.3 ) \times { 10 ^ { -9 } } ph cm ^ { -2 } s ^ { -1 } .
We argue that the linear size ( \sim 2 pc ) , the kinematic age ( \sim 100 years ) , and the source distance ( z = 0.014 ) make PKS 1718 - 649 an ideal candidate for \gamma -ray detection in the framework of the model proposing that the most compact and the youngest CSOs can efficiently produce GeV radiation via inverse-Compton scattering of the ambient photon fields by the radio lobe non-thermal electrons .
Thus , our detection of the source in \gamma -rays establishes young radio galaxies as a distinct class of extragalactic high-energy emitters , and yields a unique insight on the physical conditions in compact radio lobes interacting with the interstellar medium of the host galaxy .