Abstract:
A mechanism for producing the high energy γ-ray spectrum of X-ray binaries exhibiting ultra-high-energy activity is proposed. γ-rays can result from decay of π
0 produced in collisions of energetic protons with the keV ambient photons. Consequently, the X-ray photons modify the produced primary spectrum by selectively absorbing the lower energy part of it. As a result of this differential absorption these systems should exhibit a power law spectrum of index 1.5 - 2.0. Moreover, these systems should have a high electron-positron pair number density that will lead to 511 keV annihilation line emission.
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