Super-Keplerian equatorial outflows in SS 433

Abstract

Context. The microquasar SS 433 is the only known steady supercritical accretor in the Galaxy. It is well-known for its relativistic baryonic jets, but the system also drives equatorial outflows. These have been routinely detected in radio images, and components associated with a circumbinary disk have also been suggested in optical emission lines. Aims. We aim to spatially resolve the regions producing the stationary emission lines of SS 433 to shed light on its circumbinary structure and outflows. With an estimated binary orbit size of ≲0.1 mas, this requires optical interferometry. Methods. We use the optical interferometer VLTI+GRAVITY to spatially resolve SS 433 in the near-infrared K band at high spectral resolution (R ≈ 4000) on three nights in July 2017. This is the second such observation, after the first one in July 2016. Results. The stationary Brγ line in the 2017 observation is clearly dominated by an extended ∼1 mas ∼ 5 AU circumbinary structure perpendicular to the jets with a strong rotation component. The rotation direction is retrograde relative to the jet precession, in accordance with the slaved disk precession model. The structure has a very high specific angular momentum and is too extended to be a stable circumbinary disk in Keplerian rotation; interpreting it as such leads to a very high enclosed mass M ≳ 400 M⊙. We instead interpret it as the centrifugal ejection of the circumbinary disk, with the implication that there must be an efficient transfer of specific angular momentum from the binary to the disk. We suggest that the equatorial outflows sometimes seen in radio images result from similar episodes of circumbinary disk centrifugal ejection. In addition to the equatorial structure, we find a very extended ∼6 mas ∼ 30 AU spherical wind component to the Brγ line: the entire binary is engulfed in an optically thin spherical line emission envelope.

Collimated radiation in SS 433

“…to perform simultaneous fits for the Brγ line and the jets. For the model and results for the Brγ stationary line we refer to the companion paper on the equatorial outflows (Waisberg et al 2019). The results presented here correspond to the "outflow" model in the companion paper (which we favor over the "disk" model).…”

“…In the 2017 observations, in which there is strong blending between the jets and the Brγ stationary line, a combined fit is done, but we show only the jet model for clarity. For the Brγ stationary line model and results, we refer to the companion paper on the equatorial outflows (Waisberg et al 2019…”

“…We suggest that there may be substantial A V 1 and structured circumstellar extinction in SS 433, affecting the equatorial part of the system more than the optical jets. It may be caused by dust forming from the equatorial outflows seen in radio (Paragi et al 1999;Blundell et al 2001) and near-infrared stationary emission lines (Waisberg et al 2019). Mid-infrared observations of SS 433 show evidence of dust from excess emission at λ 20 µm (Fuchs et al 2006).…”

“…Table 1 shows the precessional φ prec and orbital φ orb phases of each observation based on the ephemerides in Eikenberry et al (2001) and Goranskij (2011), respectively. For more details on the observations and data reduction, including the uv coverage of the observations, we refer to the companion paper on the equatorial outflows (Waisberg et al 2019). In light of a slightly improved jet model, we also reanalyze the 2016 observation (Paper I), which is included in Table 1.…”

“…There are stationary emission lines (Brγ, He I 2.06 µm, He I 2.11 µm, and high order (upper levels 19-24) Pfund lines) as well as emission lines from the baryonic jets. For the analysis of the stationary Brγ line, we refer to the companion paper on the equatorial outflows (Waisberg et al 2019). In this paper, we focus on the jets.…”