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 $\sim 6.2\sigma$. The average 0.1--300~GeV flux is measured to be $(1.6\pm 0.6)\times 10^{-8}\mathrm{ph}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$, 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.

The paper was accepted by ApJ