SS 433: the wiggle of the wind

Abstract

Context. The brilliant Balmer Hα line in the stationary emission spectrum of the Galactic microquasar SS 433 has a broad component (∼1000 km s −1 ). This is formed in the wind blowing from the accretion disk of the compact object, which orbits the centre of mass of the binary at ∼175 km s −1 with a 13-day period. The centroid of the Hα emission line formed in the wind has an imperfect memory of the motion of its source. Aims. The aim is to understand how this emission line is left with a blurred memory of the motion of the source of the wind. Methods. We analysed stationary Hα spectra, taken almost nightly over two orbital periods of the binary system. Results. The loss of memory by emission lines from the wind is easily understood quantitatively, if any parcel of wind that has been newly conditioned to radiate in Hα continues its emission for a period of days. If the decay is exponential, a mean lifetime of about two days is all that is required. This timescale is very close to what is required for the decay of Hα from the putative circumbinary disk to be responsible for the narrow components of the Hα emission line. It is also close to the timescales observed for the individual bolides that radiate Hα in the relativistic jets. Conclusions. The structure of the stationary Hα emission line is now well understood. The broad component is undoubtedly formed in the wind from the accretion disk and the two narrow components carry no such signature. Their properties are entirely consistent with an origin in a circumbinary disk. The characteristic lifetime of Hα emitting material is a few days, as observed for the relativistic bolides in the jets.

SS 433: O I lines and the circumbinary disk

“…2 of Blundell et al ( 2011); I found much the same features in my independent fits to data after +287 (Bowler 2010). The newly emergent pair of lines share much of the orbital motion of the compact object (Blundell et al 2011, Bowler 2010, as does a broad Gaussian component originating in the wind above the accretion disk (Blundell et al 2011, Bowler 2011b. The question about the state of the observations of the circumbinary disk signature after +274 was summarised as follows in Blundell et al (2011), section 3.2: "The disruption of the circumbinary disc: In the days that follow the flare, after accounting for a broad component of the Hα complex as wind and the high velocity components as the manifestation of the accretion disc, in most cases there are one or two lines unaccounted for.…”

“…O I 7772 Å spectra are very different, presenting a clean P Cygni profile with particularly deep absorption troughs to the blue when the accretion disk is close to edge on. These troughs shift in wavelength with the orbital motion of the compact object and so the line O I 7772 Å is likely to be formed (and certainly absorbed) in the slow equatorial wind (Bowler 2011b). Those spectra do not suggest any components from the high speed wind above the disk or from the accretion disk itself.…”

The Spectrum of SS 433 in the H and K Bands

“…is so strong that it tends to drown out emission from other sources. There are occasional double peaks near the center of Hα that Blundell et al (2008) and Bowler (2011Bowler ( , 2013 attributed to a rotating disk. Because they did not detect orbital radial velocity variations in the double peaks, Blundell et al (2008) concluded that the disk is a circumbinary disk or ring.…”

Yet more on the circumbinary disk of SS 433

“…The Hα radiation from any packet of gas in the wind above the accretion disk seems to fall away with a characteristic time of a few days (Bowler 2011b). Its density falls as the wind blows outwards, its ionization independent of distance from the compact object, once both the gas density in the wind and the flux of ionizing photons follow inverse square laws (Fabrika 1993; see also Osterbrock & Ferland 2006).…”