First Detection of γ -Ray Emission from the Compact Symmetric Object JVAS J1311+1658

Abstract We report the first detection of γ -ray emission from the young radio galaxy JVAS J1311+1658, classified as a compact symmetric object (CSO). This detection is characterized by a recent GeV γ -ray flare identified in Fermi-Large Area Telescope data during MJD 60032.6–60132.6, with a γ -ray source detected at a significance level of ∼6.2 σ . The average 0.1–300 GeV flux is measured to be (1.6 ± 0.6) × 10 −8 ph cm −2 s −1 , with a photon spectral index of Γ = 2.15 ± 0.185. We find that a radiative model of the radio lobes significantly underestimates the observed γ -ray emission. The strong flux and short-term variability over ∼100 days suggest that the emission likely originates from newly launched subkiloparsec-scale jets at the core. This detection provides a unique window into the extreme environments and early-stage jet activity of young radio galaxies, offering insights into their initial evolution and the formation of relativistic jets in the earliest phases of galaxy growth.