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.
