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 , 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. = + + . The values of and are given above. The value of 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 and find 0.6 at phase 0.5 and 1.2 at phase 0.75. Then 1.8 at phase 0.5 and 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.
© European Southern Observatory (ESO) 2000
Online publication: February 25, 2000