On masses of the components in SS433

TL;DR

This paper reviews indirect methods to estimate the masses of binary components in SS433, concluding it likely hosts a superaccreting black hole with a mass ratio of at least 0.6, based on X-ray and spectral analyses.

Contribution

It provides new constraints on the mass ratio and total mass of SS433 using X-ray eclipse analysis and spectral line formation, supporting the black hole hypothesis.

Findings

Mass ratio q ≥ 0.3 from X-ray eclipses

Total mass M_v + M_x ≥ 40 M_sun from spectral lines

Mass ratio q ≥ 0.6 from orbital period stability

Abstract

A huge optical luminosity of the supercritical accretion disc and powerful stellar wind in the high-mass X-ray binary SS433 make it difficult to reliably estimate the mass ratio of the binary components from spectroscopic observations. We analyze different indirect methods of the mass ratio estimate. We show that with an account of the possible Roche lobe overflow by the optical star, the analysis of X-ray eclipses in the standard and hard X-ray bands suggests the estimate $q=M_\mathrm{x}/M_\mathrm{v}\gtrsim 0.3$. We argue that the double-peak hydrogen Brackett lines in SS433 should form not in the accretion disc but in a circumbinary envelope, suggesting a total mass of $M_\mathrm{v}+M_\mathrm{x}\gtrsim 40 M_\odot$. The observed long-term stability of the orbital period in SS433 $|\dot P_b/P_b|\le 1.793\times 10^{-14}$~s$^{-1}$ over $\sim 28$ year period is used to place an independent constraint of $q\gtrsim 0.6$ in SS433, confirming its being a Galactic microquasar hosting a superaccreting black hole.