The most peculiar radio characteristics of the TeV emitting high-mass X-ray binary LS I +61 ^ { \circ } 303 are two periodicities : A large periodic outburst which exhibits the same period as the orbit ( phase \Phi ) and a second periodicity of 1667 days ( phase \Theta ) which modulates the orbital phase and amplitude of the large outburst .
Recent analysis of the radio spectral index present strong evidence for the presence of the critical transition from optically thick emission ( related to a steady jet ) to an optically thin outburst ( related to a transient jet ) as in other microquasars .
In parallel , a switch from a low/hard X-ray state to a transitional state ( e.g .
steep power law state ) would be expected .
We show how the critical transition from optically thick emission to an optically thin outburst is modulated by \Theta .
Folding over a too large \Theta interval mixes up important information about the outbursts and can yield a false picture of the emission behaviour of the source along the orbit .
We therefore analyse the implications of this long period for treatment of hard X-ray/high energy data obtained from LS I +61 ^ { \circ } 303 , e.g .
with Fermi -LAT or INTEGRAL , taking into account this long-term periodicity .