LS I +61 303 is a gamma-ray binary that exhibits an outburst at GHz frequencies each orbital cycle of \approx 26.5 ~ { } \mathrm { d } and a superorbital modulation with a period of \approx 4.6 yr. We have performed a detailed study of the low-frequency radio emission of LS I +61 303 by analysing all the archival GMRT data at 150 , 235 and 610 MHz , and conducting regular LOFAR observations within the Radio Sky Monitor ( RSM ) at 150 MHz .
We have detected the source for the first time at 150 MHz , which is also the first detection of a gamma-ray binary at such a low frequency .
We have obtained the light-curves of the source at 150 , 235 and 610 MHz , all of them showing orbital modulation .
The light-curves at 235 and 610 MHz also show the existence of superorbital variability .
A comparison with contemporaneous 15-GHz data shows remarkable differences with these light-curves .
At 15 GHz we see clear outbursts , whereas at low frequencies we see variability with wide maxima .
The light-curve at 235 MHz seems to be anticorrelated with the one at 610 MHz , implying a shift of \sim 0.5 orbital phases in the maxima .
We model the shifts between the maxima at different frequencies as due to changes in the physical parameters of the emitting region assuming either free-free absorption or synchrotron self-absorption , obtaining expansion velocities for this region close to the stellar wind velocity with both mechanisms .