  LS 5039 is one of the four TeV emitting X-ray binaries detected up to now.
The powering source of its multi-wavelength emission can be accretion in a
microquasar scenario or wind interaction in a young non-accreting pulsar
scenario. These two scenarios predict different morphologic and peak position
changes along the orbital cycle of 3.9 days, which can be tested at
milliarcsecond scales using VLBI techniques. Here we present a campaign of 5
GHz VLBA observations conducted in June 2000 (2 runs five days apart). The
results show a core component with a constant flux density, and a fast change
in the morphology and the position angle of the elongated extended emission,
but maintaining a stable flux density. These results are difficult to fit
comfortably within a microquasar scenario, whereas they appear to be compatible
with the predicted behavior for a non-accreting pulsar.
