Asymmetric jet production in the Active Galactic Nucleus of NGC1052

Context: Few Active Galactic Nuclei (AGN) reveal a double sided jet system. However, these are crucial to understand basic physical properties of extragalactic jets. Aims: We address the questions whether jets in AGN are symmetric in nature, how well they are collimated on small scales, and how do they evolve with time. Methods: We monitored the sub-parsec scale morphology of NGC1052 with the VLBA at 43GHz from 2005 to 2009. Results: A detailed study of 29 epochs show an asymmetry between both jets. A kinematic analysis of the outflows reveals higher apparent velocities for the eastern jet as compared to the western one: beta_ej = 0.529+-0.038 and beta_wj = 0.343+-0.037, respectively. Contradictory to previous studies, we find higher flux densities for the western jet. The distribution of brightness temperature and jet width features well collimated jets up to 1mas distance to the dynamic center and a nearly conical outflow further outwards. Combining flux density ratios and velocities of the jet flow, we were not able to find a combination of intrinsic velocity and inclination angle of the jets that is consistent for all observations, which is contradictory to symmetrically evolving jets. Spectral index maps between quasi-simultaneous 22GHz and 43GHz observations support the existence of an optically thick absorber covering the innermost 1.6 mas around the 43GHz central feature and an optically thin jet emission with a spectral index of <= -1. Conclusions: Our results fit into a picture in which we expect larger internal energy and/or magnetic flux in the western jet and higher kinetic energy in the eastern jet. Previous observations at lower frequencies found slower velocities of the moving jet features as compared to this work. Considering the different velocities at different areas we suggest a spine-sheath structure with a faster inner layer and a slower outer layer.