Decade-long INTEGRAL observations of SS433 confirm its nature as a super-accreting microquasar with a black hole
In the unique super-critically accreting Galactic microquasar SS433 (see
also INTEGRAL
POM December 2013),
the stability of mass transfer without
the formation of a common envelope has been a big puzzle. Evolutionary
calculations suggest that if the mass ratio of components of a massive
binary system is not very different from unity (q = Mx/Mv > 0.29,
where Mx and Mv is the mass of the relativistic compact object and
optical star, respectively), the system during the second mass transfer
stage can remain semi-detached for a long time, with the optical star
overfilling its critical Roche lobe. The decade-long INTEGRAL IBIS/ISGRI
observations of SS433 revealed the presence of a hot extended X-ray
'corona' surrounding the relativistic jets and enabled a detailed study
of three different types of regular hard X-ray (18-60 keV) variability
in the source: the orbital (eclipsing, due to the 13.6-day orbital
motion of the components), the precessional (162 days) and nutational (6
days) one (due to the motion of the accretion disc). The analysis of the
X-ray eclipses and precessional variability in the model with a
Roche-lobe filling optical star yielded the conservative estimate of the
binary mass ratio, q>0.3. This lower limit is in agreement with the
independent estimate q>0.6 as obtained from the analysis of the observed
40-years stability of the orbital period of SS433. The large binary
mass ratio in SS433 offers the explanation of the nature of this
enigmatic source as a semi-detached massive X-ray binary harbouring a
supercritically accreting stellar-mass black hole.
References:
"SS433: a massive X-ray binary at advanced evolutionary stage",
Anatol Cherepashchuk et al. 2019,
New Astronomy, submitted.
https://arxiv.org/abs/1905.02938
