  The most puzzling aspect of the radio emission from LSI+61303 is that the
large periodic radio outburst, with period equal to the orbital one, occurs
very displaced from periastron passage, nearly at apoastron. In 1992, Taylor,
one of the discoverers of this source, together with his collaborators proposed
a model of a compact object in an eccentric orbit accreting from the equatorial
wind of the Be star primary. The application of this model by Marti & Paredes
(1995) predicts one ejection at periastron and a second more displaced ejection
along the orbit. The first ejection should correspond to weak radio emission,
because of strong inverse Compton losses of the emitting electrons due to the
proximity to the hot Be star, whereas the second ejection, quite displaced from
the star, would correspond to a strong radio outburst, that one indeed
observed. Corroborated along the years by numerical computations, simulations
and gamma-ray observations, until now this two-peak model could not be proved
in the radio band, because of the negligible emission around periastron. We
show here, that the radio spectral index based on the ratio of flux densities
is the unique tool to monitor activity of LSI+61303 in the radio band around
periastron. The analysis of the radio spectral index over almost 7 years of
Green Bank Interferometer data results in a clear double-peaked spectral index
curve along the orbit. This result gives finally observational support at
radiowavelengths to the two-peak accretion/ejection model for LSI+61303.
Moreover, the here shown comparison of the two-peak curves - the radio spectral
index curve and the Fermi-LAT gamma-ray curve - indicates a new interesting
hypothesis on the electron population responsible for the gamma-ray emission.
