摘要：Context.According to radiative models, radio galaxies may produceγ-ray emission from the first stages of their evolution. However, very few such galaxies have been detected by theFermiLarge Area Telescope (LAT) so far.Aims.NGC 3894 is a nearby (z = 0.0108) object that belongs to the class of compact symmetric objects (CSOs, i.e., the most compact and youngest radio galaxies), which is associated with aγ-ray counterpart in the FourthFermi-LAT source catalog. Here we present a study of the source in theγ-ray and radio bands aimed at investigating its high-energy emission and assess its young nature.Methods.We analyzed 10.8 years ofFermi-LAT data between 100 MeV and 300 GeV and determined the spectral and variability characteristics of the source. Multi-epoch very long baseline array (VLBA) observations between 5 and 15 GHz over a period of 35years were used to study the radio morphology of NGC 3894 and its evolution.Results.NGC 3894 is detected inγ-rays with a significance >9σover the full period, and no significant variability has been observed in theγ-ray flux on a yearly time-scale. The spectrum is modeled with a flat power law (Γ = 2.0 ± 0.1) and a flux on the order of 2.2 × 10−9ph cm−2s−1. For the first time, the VLBA data allow us to constrain with high precision the apparent velocity of the jet and counter-jet side to beβapp, NW = 0.132 ± 0.004 andβapp, SE = 0.065 ± 0.003, respectively.Conclusions.Fermi-LAT and VLBA results favor the youth scenario for the inner structure of this object, with an estimated dynamical age of 59 ± 5 years. The estimated range of viewing angle (10° <θ < 21°) does not exclude a possible jet-like origin of theγ-ray emission.
