Peculiarities in the orbital and precessional variability of SS433 from INTEGRAL observations

Abstract

Based on multiyear INTEGRAL observations of SS433, a composite IBIS/ISGRI 18-60 keV orbital light curve is constructed around zero precessiona l phase ψpr = 0, which corresponds to a maximum separation of the moving emission lines originated in sub-relativistic jets from the source. It shows a peculiar shape characterized by a signific ant excess near the orbital phase φorb = 0.25, which is not seen in the softer 2-10 keV energy band. Such a shape is likely to be due to a complex asymmetric structure of the funnel in a supercritical accretion disk in SS433. The orbital light curve at 40-60 keV demonstrates two almost equal bumps at phases ∼ 0.25 and ∼ 0.75, most likely due to nutation effects of the accretion disk . The change of the offeclipse 18-60 keV X-ray flux with the precessional phase show s a double-wave form with strong primary maximum at ψpr = 0 and weak but significant secondary maximum at ψpr = 0.6. A weak variability of the 18-60 keV flux in the middle of the orbi tal eclipse correlated with the disk precessional phase is also observed. The joint analysi s of the broadband (18-60 keV) orbital and precessional light curves obtained by INTEGRAL confirms the presence of a hot extended corona in the central parts of the supercritical accretion d isk and constrain the binary mass ratio in SS433 in the range 0.5& q& 0.3, confirming the black hole nature of the compact object. Orb ital and precessional light curves in the hardest X-ray band 40-60 keV, which is free from emission from thermal X-ray jets, are also best fitted by the same geome trical model with hot extended corona at q ∼ 0.3, stressing the conclusions of the modeling of the broad-band X-ray orbital and precessional light curves.