Hints for a fast precessing relativistic radio jet in LS I+61 degrees 303

Here we discuss two consecutive MERLIN observations of the X-ray binary LS I+61degrees303. The first observation shows a double-sided jet extending up to about 200 AU on both sides of a central source. The jet shows a bent S-shaped structure similar to the one displayed by the well-known precessing jet of SS 433. The precession suggested in the first MERLIN image becomes evident in the second one, showing a one-sided bent jet significantly rotated with respect to the jet of the day before. We conclude that the derived precession of the relativistic (beta=0.6) jet explains puzzling previous VLBI results. Moreover, the fact that the precession is fast could be the explanation of the never understood short term ( days) variability of the associated gamma-ray source 2CG 135+01/3EG J0241+6103.