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Astron. Astrophys. 322, 523-532 (1997)

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Cascade initiated by VHE [FORMULA] -rays in the radiation field of a close massive companion

W. Bednarek

Department of Experimental Physics, University of Lódz, ul. Pomorska 149/153, PL-90236 Lódz, Poland

Received 13 September 1996 / Accepted 4 December 1996


Two massive binaries, Cyg X-3 and LSI  [FORMULA] +61, are inside the error boxes of [FORMULA] -ray sources detected by the Compton GRO. If somewhere inside such binary systems are injected very high energy (VHE) [FORMULA] -rays, as suggested by some Cherenkov observations, they may initiate the inverse Compton [FORMULA] pair cascade in the soft radiation of a massive companion, and the detected high energy [FORMULA] -ray emission may be caused by the secondary [FORMULA] -rays of such cascade process. Since VHE [FORMULA] -rays has to propagate in the anisotropic radiation of a massive star (the place of injection does not cover with the source of soft radiation), the intensities of secondary [FORMULA] -rays depend on the angles of observation measured from direction defined by the place of injection of VHE [FORMULA] -rays and the center of a massive star. We compute [FORMULA] -ray spectra formed in such anisotropic cascade by using the Monte Carlo method. It is found that the intensity of secondary [FORMULA] -rays does not varies strongly for the angles of observation greater than [FORMULA], but the highest intensities are observed at the angles corresponding to the limb of a massive star. Moreover, some cascade [FORMULA] -rays can also emerge from behind the massive star, i.e. from the opposite site than the location of a source of primary [FORMULA] -rays. This interesting feature can be called as a focusing of [FORMULA] -rays by the soft radiation of a massive star.

Key words: {gamma-rays: general -- stars: binaries: close -- stars: individual: LSI+$61^o$303, Cyg X-3}

Send offprint requests to: Bednar@krysia.uni.lodz.pl

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© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998