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Astron. Astrophys. 362, 646-654 (2000)

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Escape of VHE gamma-rays from close massive binary Centauri X-3

W. Bednarek

Department of Experimental Physics, University of ód, ul. Pomorska 149/153, 90-236 ód, Poland (Bednar@krysia.uni.lodz.pl)

Received 3 July 2000 / Accepted 31 August 2000

Abstract

We consider propagation of very high energy (VHE) gamma-rays in the radiation field of a massive star in the binary system Cen X-3, which has been reported as a source of gamma-ray photons in the GeV and TeV energies. VHE gamma-rays or electrons, injected by the compact object, should develop inverse Compton [FORMULA] pair cascades. Based on the Monte Carlo simulations we predict the [FORMULA]-ray spectra and the [FORMULA]-ray light curves for the parameters of Cen X-3 system, and applying different models of injection of primary particles (monodirectional, isotropic, monoenergetic, power law). It is found that the gamma-ray spectra observed at different directions have different shapes and intensities. Interestingly, some gamma-rays may even escape from the binary system at directions which are obscured by the massive star, i.e. from the opposite side of the massive star to the location of the compact source of primary gamma-rays or electrons. We predict that the gamma-ray light curves, produced in the case of electron injection by the compact object in the Cen X-3 system, should have opposite tendencies for photons with energies above 100 MeV and above 300 GeV, i.e. the photon intensities increase with phase in the first case and decrease with phase in the second case. However the model with injection of primary electrons seems to be contrary to the reported modulation of the GeV [FORMULA]-ray flux with the pulsar's period. The model with injection of primary photons allows such modulation with the pulsar's period, but predicts strong modulation of the TeV flux with the orbital period of the binary. Modulation of TeV emission with the orbital period was reported by the early Cherenkov observations, but was not confirmed by the recent, more sensitive observations by the Durham Mark 6 telescope.

Key words: stars: binaries: close – stars: individual: Cen X-3 – gamma rays: theory

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© European Southern Observatory (ESO) 2000

Online publication: October 24, 2000
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