An optical spectroscopic and polarimetric study of the microquasar binary system SS 433

Abstract

Aims. Our aim is to study the mass transfer, accretion environment, and wind outflows in the SS 433 system, concentrating on the so-called stationary lines. Methods. We used archival high-resolution (X-shooter) and low-resolution (EMMI) optical spectra, new optical multi-filter polarimetry, and low-resolution optical spectra (Liverpool Telescope), spanning an interval of a decade and a broad range of precessional and orbital phases, to derive the dynamical properties of the system. Results. Using optical interstellar absorption lines and H I 21 cm profiles, we derive E(B − V) = 0.86 ± 0.10, with an upper limit of E(B − V) = 1.8 ± 0.1 based on optical Diffuse Interstellar Bands. We obtain revised values for the ultraviolet and U band polarizations and polarization angles (PA), based on a new calibrator star at nearly the same distance as SS 433 that corrects the published measurement and yields the same PA as the optical. The polarization wavelength dependence is consistent with optical-dominating electron scattering with a Rayleigh component in U and the UV filters. No significant phase modulation was found for PA while there is significant variability in the polarization level. We fortuitously caught a flare event; no polarization changes were observed but we confirm the previously reported associated emission line variations. Studying profile modulation of multiple lines of H I, He I, O I, Na I, Si II, Ca II, Fe II with precessional and orbital phase, we derive properties for the accretion disk and present evidence for a strong disk wind, extending published results. Using transition-dependent systemic velocities, we probe the velocity gradient of the wind, and demonstrate that it is also variable on timescales unrelated to the orbit. Using the rotational velocity, around 140 ± 20 km s−1, a redetermined mass ratio q = 0.37 ± 0.04, and masses MX = 4.2 ± 0.4 M⊙, MA = 11.3 ± 0.6 M⊙, the radius of the A star fills – or slightly overfills – its Roche surface. We devote particular attention to the O I 7772 Å and 8446 Å lines, finding that they show different but related orbital and precessional modulation and there is no evidence for a circumbinary component. The spectral line profile variability can, in general, be understood with an ionization stratified outflow predicted by thermal wind modeling, modulated by different lines of sight through the disk produced by its precession. The wind can also account for an extended equatorial structure detected at long wavelength.

Progress in Understanding the Nature of SS433

“…Similar results were obtained by [33]. In the recent paper by [34], the axial rotation velocity v rot = 140 ± 20 km s −1 was measured using the Doppler widening of absorption lines of the optical star. Using this value, the corresponding masses and mass ratio of the components of SS433 were estimated: q = M x Mv = 0.37 ± 0.04, the mass of the relativistic object M x = 4.2 ± 0.4M and the mass of the optical star M v = 11.3 ± 0.6M .…”

A Systematic View of Ten New Black Hole Spins

“…Therefore, despite emerging evidence that SS 433 may harbor a BH rather than a neutron star (e.g., Picchi et al 2020), SS 433 fails several of our criteria for examination, and it is excluded from our analysis. However, Fogantini et al (2023) performed an analysis of the spectra obtained from the 10 NuSTAR observations of SS 433.…”

An Overview of Compact Star Populations and Some of Its Open Problems

“…For the velocity semi-amplitude, we adopt the reported K cp = 58.2 ± 3.1 km s −1 from Picchi et al [185], and, for consistency, also adopt the mass estimates from that same work, M BH = 4.2 ± 0.4 M and M cp = 11.3 ± 0.6 M , which result in a mass ratio q ≈ 2.64.…”