Unique microquasar SS433: new results, new issues

TL;DR

SS433 is a unique Galactic microquasar that hosts a precessing supercritical accretion disk and relativistic jets, offering a nearby laboratory for extreme accretion physics. By compiling ~45 years of spectral and photometric data, the study tests the slaved disk model, constrains jet kinematics with a kinematic model, and documents a secular rise in the orbital period while confirming an elliptically distorted orbit. The analysis yields $M_{ m x} \\gtrsim 8\,M_$ and $q \ geq 0.8$, demonstrates that the binary separation grows while the donor fills an outer Roche lobe, and reveals phase jumps in precession tied to disk viscous timescales, along with evidence for a substantial third light and a hot corona driving hard X-ray emission. The results also highlight gamma-ray and TeV detections suggesting hadronic acceleration and potential Galactic PeVatron activity, underscoring SS433 as a key laboratory for supercritical accretion, jet formation, and high-energy processes in compact binaries.

Abstract

The unique microquasar SS433 is a massive X-ray binary system at an advanced evolutionary stage. The optical star overflows its Roche lobe and transfers mass at a very high rate onto a black hole surrounded by a supercritical accretion disk with relativistic jets inclined to the orbital plane. Both disk and jets precess with a period of 162.3 days. In the outer parts of the precessing jets, emission lines of hydrogen and neutral helium are formed, moving periodically across the spectrum of SS433 with an enormous amplitude of $\sim 1000$\,Å or, on the $\sim 50000$ km/s velocity scale. A 30-year spectral and photometric monitoring of SS433 has been carried out at Sternberg Astronomical Institute. Using all published data for 45 years of observations, we obtained a number of important results concerning the nature of this unique microquasar. We discovered a secular evolutionary increase in the orbital period of SS433 at a rate of $(1.14 \pm 0.25)\times 10^{-7}$ seconds per second, suggesting that the relativistic object in SS433 is a black hole with mass exceeding 8\,${\rm M}_\odot$. It is shown that the distance between the components of SS433 increases with time, which prevents the formation of a common envelope in the system. The size of the Roche lobe of the optical donor star is on average constant in time, which ensures a stable secondary mass exchange in the system. The orbital ellipticity of SS433 was discovered, strongly supporting the model of a slaved accretion disk tracking the precession of the rotation axis of the optical star, which is inclined to the orbital plane due to an asymmetric supernova explosion. Parameters of the kinematic model of SS433, except for the precession period, keep on average constant for 45 years. Phase jumps of the precession period were detected, but on average the precession period remains constant for 45 years. (Abridged)

Figures (21)

• Figure 1: Sequence of SS433 spectra showing the stationary and moving hydrogen emission lines H$\alpha$ (6563Å). The spectra are marked by modified Julian days (MJD, counted from midnight).
• Figure 2: Stationary and moving emissions in the spectrum of SS433. Sequence of SS433 spectra obtained in summer-autumn 2023 at the Caucasus Mountrain Observatory of SAI MSU. On the ordinate axis -- time in modified Julian days.
• Figure 3: Structure of moving H$\alpha$ emissions formed in relativistic jets. Three spectra of SS433 obtained with an interval of two days. One can see the effect of gradual fading of the moving line and the multicomponent structure of the moving lines, partly explained by the fading effect. The moving line component and its residual afterglow are connected by blue dashed lines.
• Figure 4: Precession-nutation displacement of moving lines. The time interval corresponds to Fig. \ref{['f:tds']}. Gray curve corresponds to the kinematic model with parameters found from the time interval shown. The Doppler shifts of the blue and red H$\alpha$ emissions as a function of time are plotted on the ordinate axis.
• Figure 5: Parameters of the kinematic model of SS 433 (see Tables \ref{['t:precpar']} and \ref{['t:nutpar']}). The bold dots on the right (the 14th interval) are derived from new data.