Analysis of hard X-ray/high energy data from LS I +61°303 based on implications from its 4.6 yr periodicity

Abstract: The most peculiar radio characteristics of the TeV emitting high-mass X-ray binary LS I +61{\deg}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{\deg}303, e.g. with Fermi-LAT or INTEGRAL, taking into account this long-term periodicity.