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

The analysis of INTEGRAL observations (2003-2008) of superaccreting galactic microquasar SS433 at precessional phases with the maximum disk opening angle is carried out. The shape and width of the primary X-ray eclipse is found to be strongly variable suggesting additional absorption in dense stellar wind and gas outflows from the optical A7I-component. The joint modeling of X-ray eclipse and precessional X-ray variability by a geometrical model suggests the binary mass ratio q=m_x/m_v=0.3, allowing an explnation of peculiarities of the optical variability of SS433, in particular, the substantial precessional variability at the primary optical eclipse minimum. For the mass function of the optical star f_v=0.268 M_\odot as derived from Hillwig and Gies (2008) data, the obtained q yields the masses of the components m_x=5 M_\odot, m_v=15 M_\odot, confirming the black hole nature of the relativistic object in SS433. The independence of the observed hard X-ray spectrum on the precession phase suggests that hard X-ray emission is formed in an extended hot corona. The Monte-Carlo simulations of the broadband X-ray spectrum of SS433 at the maximum disk opening precessional phases allowed us to determine physical parameters of the corona (temperature T_{cor}=20 keV, Thomson optical depth \tau=0.2), and to estimate the jet mass outflow rate \dot M_j=3\times 10^{19} g/s yielding the kinetic power of the jets \sim 10^{39} erg/s.Comment: 12 pages, 10 figures, Proc. 7th INTEGRAL Workshop, Copenhagen, 8-11 September 200

Mass ratio in SS433 revisited

We revisit the determination of binary mass ratio in the Galactic microquasar SS433 based on recent GRAVITY VLTI measurements of mass and angular momentum outflow through a circumbinary disc. The new observations combined with the constancy of the binary orbital period over $\sim 30$ yrs confirm that the mass ratio in SS433 is $q=M_\mathrm{x}/M_\mathrm{v}\gtrsim 0.6$. For the assumed optical star mass $M_\mathrm{v}$ ranging from $\sim 8$ to 15 $M_\odot$ such a mass ratio suggests a low limit of the compact object mass of $M_\mathrm{x}\sim 5-9 M_\odot$, placing the compact object in SS433 as a stellar-mass black hole.Comment: 4 pages, 3 figures, accepted in MNRAS, Main Journa

Apsidal advance in SS 433?

Context. The Galactic microquasar SS 433 launches oppositely directed jets at speeds approximately a quarter of the speed of light. Both the speed and direction of the jets exhibit small fluctuations. A component of the speed variation has 13 day periodicity and the orbital phase at which its maximum speed occurs has advanced approximately 90 degrees in 25 years. Aims. To examine the possibility that these variations are associated with a mildly eccentric orbit and conditions necessary to achieve this apsidal advance. Methods. The advance of the orbital phase for maximum speed is taken to be advance of the apses of the putative elliptical orbit. It is compared with calculations of the effects of tides induced in the companion and also with gravitational perturbations from the circumbinary disc. These calculations are made in the light of recent results on the SS 433 system. Results. The 13 day periodicity in the speed of the jets of SS 433 might be attributed to a mildly elliptical orbit, through periodic approaches of the donor and the compact object. Advance of the apses of such an elliptical orbit due to tidal effects induced in a normal companion looks to be to small; if caused by the circumbinary disc the mass of the inner regions of that disc is ~ 0.15 solar masses.Comment: 2 pages, no figures To appear in A & A. No significant changes from original version poste

INTEGRAL observations of SS433, a supercritically accreting microquasar with hard spectrum

Observations of SS433 by INTEGRAL carried out in March -- May 2003 are presented. SS433 is evidently detected on the INTEGRAL images of the corresponding sky region in the energy bands 25-50 and 50-100 keV. The precessional variability of the hard X-ray flux is clearly seen. The X-ray eclipse caused by the binary orbital motion is also detected. A possible origin of the hard continuum is briefly discussed.Comment: 5 pages, 6 figures. Accepted to A&A INTEGRAL special volum