Peculiar nature of hard X-ray eclipse in SS433 from INTEGRAL observations

• Published in: Monthly notices of the Royal Astronomical Society 2009-07, Vol.397 (1), p.479-487
• Main Authors: Cherepashchuk, A. M., Sunyaev, R. A., Postnov, K. A., Antokhina, E. A., Molkov, S. V.
• Format: Article
• Language: English
• Subjects: Accretion disks; binaries: eclipsing; Double stars; X-ray astronomy; X-rays: binaries; X-rays: individual: SS433
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2009.14948.x

The analysis of hard X-ray INTEGRAL observations (2003–2008) of superaccreting Galactic microquasar SS433 at precessional phases of the source with the maximum disc opening angle is carried out. It is found that the shape and width of the primary X-ray eclipse are strongly variable, suggesting additional absorption in dense stellar wind and gas outflows from the optical A7I component and the wind–wind collision region. The independence of the observed hard X-ray spectrum on the accretion disc precessional phase suggests that hard X-ray emission (20–100 keV) is formed in an extended, hot, quasi-isothermal corona, probably heated by interaction of relativistic jet with inhomogeneous wind outflow from the precessing supercritical accretion disc. A joint modelling of X-ray eclipsing and precessional hard X-ray variability of SS433 revealed by INTEGRAL by a geometrical model suggests the binary mass ratio q=mx/mv≃ 0.25–0.5. The absolute minimum of joint orbital and precessional χ2 residuals is reached at q≃ 0.3. The found binary mass ratio range allows us to explain the substantial precessional variability of the minimum brightness at the middle of the primary optical eclipse. For the mass function of the optical star fv= 0.268 M⊙ as derived from Hillwig & Gies data, the obtained value of q≃ 0.3 yields the masses of the components mx≃ 5.3 M⊙, mv≃ 17.7 M⊙, confirming the black hole nature of the compact object in SS433.