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

Peculiar nature of hard X-ray eclipse in SS433 from INTEGRAL observations. Anatol Cherepashchuk Sternberg Astronomical Institute, Moscow University, Russia In collaboration with: Rashid Sunyaev (IKI), Eleonora Antokhina, Konstantin Postnov, Sergey Molkov (CESR). INTRODUCTION: SS 433.

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

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  1. Peculiar nature of hard X-ray eclipse in SS433 from INTEGRAL observations Anatol Cherepashchuk Sternberg Astronomical Institute, Moscow University, Russia In collaboration with: Rashid Sunyaev (IKI), Eleonora Antokhina, Konstantin Postnov, Sergey Molkov (CESR) HEA-2008, IKI

  2. INTRODUCTION: SS 433 • A massive eclipsing binarysystem • Consists of a massive donor star and a compact • object, surrounded by precessing accretion disk • Narrow-collimated relativistic jets (v ~ 0.26 c) • Precessional period P=162.5 d • Orbital period p=13.082 d • A problem with spectral classification of the optical star (the disk is significantly more luminous) One of the main questions - the nature of the relativistic object (BH or NS ?) HEA-2008, IKI

  3. Reliable radial velocity curve of the optical component Reliable detection of absorption lines of the optical A3-7I star New high-resolution spectroscopy of SS433 (Hillwig & Gies 2008) HEA-2008, IKI

  4. Kv=58.2+/-3.1 km/s (from absorption lines) • Kx=168+/-18 km/s (from HeII emission line) • Mass ratio q=Mx/Mv=0.35 • Optical star mass function fv(M)=0.268 Msun • Masses os the components: Mv=12.3+/-3.3 Msun Mx=4.3 +/- 0.8 Msun HEA-2008, IKI

  5. Main hard X-ray features revealed by INTEGRAL AO1-AO5 • First observations gave a surprise: SS433 is a hard X-ray source with emission clearly detected up to 100 keV  SS433 is galactic microquasar with hard X-ray spectrum (AMCh et al 2003) • Strong precessional variability in hard X-rays with an amplitude Lxmax/Lxmin ~ 7 • Peculiar and variable shape of ascending eclipse branch • Wide, deep hard X-ray eclipse (wider than in soft X-rays!) • Hard X-ray spectrum independent of the precessional phase HOT EXTENDED CORONA HEA-2008, IKI

  6. All INTEGRAL observations HEA-2008, IKI

  7. Precessional variability • Strong precessional 162-d variability was found with a maximum to minimum flux ratio of ~7 • Flux at primary minima is non-zero: ~ 3 mCrab, suggesting extended hard X-ray emitting region HEA-2008, IKI

  8. Analysis of hard X-ray spectra • To increase statistical significance, we splitted the precessional light curve on two parts: “high” (maximum X-rya flux) and “low” (<10 mCrab). Both are consistent with power law. HEA-2008, IKI

  9. T3 Average precessional light curve with AO5 data added HEA-2008, IKI

  10. II(1.025<Ψprec <1.125 & 0.875<Ψprec <0.975) III (0.5<Ψprec <0.8 & 1.2<Ψprec <1.5) I (0.975<Ψprec <1.025) 20-200 keV spectra (IBIS/ISGRI). Power-law photon index Γ=2.8 for all spectra! HEA-2008, IKI

  11. Orbital eclipses primary max. crossover I • Several orbital eclispses were observed at different precessional phases crossover II Second. max. HEA-2008, IKI

  12. Individual eclipses at T3 IBIS/ISGRI 18-60 keV HEA-2008, IKI

  13. Mass ratio from hard X-ray eclipses • In the standard X-ray range 1-10 keV: q~0.1-0.15 (Kawai et al. 1989, Kotani et al. 1996); due to a very wide X-ray eclipse • In the hard X-ray range (18-60 keV) the eclipse form and width are very variable. HEA-2008, IKI

  14. Egress from the primary eclipse is extremely variable (presumably due to gaseous streams from ther star and stellar wind from the disk) • Ingress to the primary eclipse is much more stable • Interpretation of the primary eclipse by geometrical model should be based on the upper envelope of the eclipse ingress HEA-2008, IKI

  15. Fitting of theprimary eclipse (ingress) together with precessional light curve yields q=0.3, in agreeement with optical spectroscopic determination by Hillwig & Gies HEA-2008, IKI

  16. Model for variability • The optical star fills it Roche lobe • The accretion disk is approximated by an oblate spheroid • X-ray flux is emitted by the hot “corona” around the base • of the narrow relativistic jets • The“corona” is approximated by the spheroid and • precesses along with disk • The “corona” is placed inside the “funnel” at the inner parts • of the disk • During the orbital and precessional moving the “corona” is • eclipsed by the star and disk bodies s s HEA-2008, IKI

  17. Results for q=0.1: Good fit to eclipse, bad fit to precessional variability • In principle, long thick X-ray jet yields a good fit to the orbital eclipse, but totally fails to describe the precessional light curve! •  Joint analysis is needed. HEA-2008, IKI

  18. Joint analysis of orbital eclipses (ingress only) and precessional variability: q=0.3 HEA-2008, IKI

  19. Orbital + precessional chi-2 for different q Mv<15 Msun Sum of the reduced orbital and precessional chi-2 HEA-2008, IKI

  20. Monte-Carlo analysis of broadband (2-100 keV) X-ray spectrum and parameters of hard X-ray corona JEMX+IBIS May 2003 Jet: dM/dt~ 10-7 Msun/yr Lkin~1039 erg/s Corona: kTc~20 keV Rc~6x1011cm τc~ 0.2-03 ne~ 4x1012cm-3 (Krivosheev et al. 2008) HEA-2008, IKI

  21. Conclusions • Our correct analysis of hard X-ray eclipses and precessional variability in SS433 allowed independent determination of the binary mass ratio q=Mx/Mv=0.3, in full agreement with optical spectroscopic result by Hillwig & Gies (2008). The compact object mass is Mx=5 Msun, Mv=15 Msun confirming its nature as a black hole HEA-2008, IKI

  22. INTEGRAL orbital and precessional light curves of SS433 can be interpreted by an extended corona above the superaccreting disk around the black hole. Thin relativistic jets shining in soft X-rays are generated from the center of the corona that is observed in hard X-rays HEA-2008, IKI

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