A possible EGRET source with a two-sided radio jet structure on a parsec scale - 3EG J0808+5114

Abstract

We report on the European VLBI Network observations of the radio source 0803+5126 in the field of the Energetic Gamma Ray Experiment Telescope (EGRET) source 3EG J0808+5114. High-resolution images of 0803+5126 at 6 cm showed a core emission with an extremely low brightness temperature plus an asymmetric two-sided jet structure on both parsec and tens of parsec scales, suggesting a relatively weak beaming effect in radio emission. The radio structures on different scales exhibit quite different orientations of extension, indicating the occurrence of jet bending. Based on the positional uncertainty of 3EG J0808+5114, its separations to various possible radio counterparts, and very low gamma-ray variability, it is reasonable to believe that 0803+5126 is the most probable radio counterpart of 3EG J0808+5114, making it the first EGRET-detected active galactic nucleus to be associated with a two-sided jet structure on a parsec scale. The central engine is estimated to have a mass of similar to 5.0 x 10(8) M-circle dot by using Mg II emission line features, for which the Eddington limit is approximately two times lower than the integrated gamma-ray luminosity. The minimum Doppler factor in gamma-ray emission is similar to 2.5, but the true one should not be much larger than this value on account of its quiet stable gamma-ray emission. This is consistent with our very long baseline interferometry results of the two-sided radio jet structure. The relativistic beaming effect and downstream jet bending may play an important role in the paradox between the large gamma-ray luminosity far above its Eddington limit and the observed asymmetric two-sided radio structure.