Inverse Compton e-p pair cascade model for the gamma-ray production in massive binary LSI +61^o 303

Abstract

We apply an inverse Compton $e^\pm$ pair cascade model for $γ$-ray production in massive binary system LSI +61$^{\rm o}$ 303 assuming that electrons are accelerated already inside the inner part of the jet launched by the compact object. $γ$-ray spectra, affected by the cascade process, and lower energy spectra, from the synchrotron cooling of the highest energy electrons in the jet, are calculated as a function of the phase of this binary system. $γ$-ray spectra expected in such model have different shape than that ones produced by electrons in the jet directly to observer. Moreover, the model predicts clear anti-correlation between $γ$-ray fluxes in the GeV (1-10 GeV) and TeV ($>200$ GeV) energy ranges with the peak of the TeV emission at the phase $\sim$0.5 (the peak half width ranges between the phases $\sim$0.4-0.9 for the inclination of the binary system equal to $60^{\rm o}$, and $\sim$0.4-0.1 for $30^{\rm o}$). The fine features of TeV $γ$-ray emission (fluxes and spectral shapes) as a function of the phase of the binary system are consistent with recent observations reported by the MAGIC collaboration. Future simultaneous observations in the GeV energies (by the GLAST and AGILE telescopes) and in the TeV energies (by the MAGIC and VERITAS telescopes) should test other predictions of the considered model supporting or disproving the hypothersis of acceleration of electrons already in the inner part of the microquasar jets.