First Detection of $\gamma$-Ray Emission from the Compact Symmetric Object JVAS J1311+1658

Abstract

We report the first detection of $\gamma$-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 $\gamma$-ray flare identified in Fermi-LAT data during MJD~60032.6--60132.6, with a $\gamma$-ray source detected at a significance level of $\sim6.2\sigma$. The average 0.1--300~GeV flux is measured to be $(1.6 \pm 0.6)\times10^{-8}\,\mathrm{ph\,cm^{-2}\,s^{-1}}$, with a photon spectral index of $\Gamma = 2.15 \pm 0.185$. We find that a radiative model of the radio lobes significantly underestimates the observed $\gamma$-ray emission. The strong flux and short-term variability over $\sim$100 days suggest that the emission likely originates from newly launched sub-kiloparsec-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.