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Astron. Astrophys. 354, 983-986 (2000)

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6. Modulation of X-rays in Cyg X-3

We can now construct the picture of modulation of hard and soft X-radiation from Cyg X-3, using the above calculations. The observed modulation is due to scattering of radiation by electrons between the X-ray source and the observer. In the case of the hard X-radiation, the radiation comes from the black hole. At phase 0.5 the maximum radiation is seen, when the combined Compton scattering optical depth [FORMULA], due to the post-shock gas, the ionised region due to the X-rays from the black hole and the Wolf-Rayet wind, towards the observer is minimum. [FORMULA]= [FORMULA]+ [FORMULA]+ [FORMULA]. The values of [FORMULA] and [FORMULA] are given above. The value of [FORMULA] is not known. If we use the observed ratio of intensities at phases 0.5 and 0.75 (Hermsen et al. 1987), we can adjust [FORMULA] and find [FORMULA][FORMULA]0.6 at phase 0.5 and [FORMULA][FORMULA]1.2 at phase 0.75. Then [FORMULA] [FORMULA]1.8 at phase 0.5 and [FORMULA]2.1 at phase 0.75, resulting in the reduced hard X-ray intensity at phase 0.75. At phase 0.0, the hard radiation is strongly attenuated by the accretion wake and leads to the minimum observed.

The soft X-radiation seen by the observer is a combination of the emission from the black hole and the radiation from the hot post-shock gas. This however is modulated by the attenuation due to the wind of the Wolf-Rayet star.The amount of soft X-radiation emission towards the observer from the hot post shock gas increases from pkase 0.5 to phase 0.75 as the attenuation due to the Wolf-Rayet wind decreases. The soft radiation as seen by the observer quickly drops beyond phase 0.75 due to the combined effects of decreasing solid angle subtended by the hot post- shock emitting region, the attenuation by the post shock gas and the increasing attenuation by the wind of the Wolf-Rayet star. At phase 0.0 the soft X-radiation is completely attenuated by the gas in the accretion wake.

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© European Southern Observatory (ESO) 2000

Online publication: February 25, 2000
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