X-ray variability of SS 433: Evidence for supercritical accretion

We study the X-ray variability of SS 433 based on data from the ASCA observatory and the MAXI and RXTE/ASM monitoring missions. Based on the ASCA data, we have constructed the power spectrum of SS 433 in the frequency range from 10^?6 to 0.1 Hz, which confirms the presence of a flat portion in the spectrum at frequencies 3 × 10^?5?10^?3 Hz. The periodic variability (precession, nutation, eclipses) begins to dominate significantly over the stochastic variability at lower frequencies, which does not allow the stochastic variability to be studied reliably. The model in which the flat portion extends to 9.5 × 10^?6 Hz, while a power-law rise with an index of 2.6 occurs below provides the best agreement with the observations. The nutational oscillations of the jets with a period of about three days suggests that the time for the passage of material through the disk is less than this value. At frequencies below 4 × 10^?6 Hz, the shape of the power spectrum probably does not reflect the disk structure but is determined by external factors, for example, by a change in the amount of material supplied by the donor. The flat portion can arise from a rapid decrease in the viscous time in the supercritical or radiative disk zones. The flat spectrum is associated with the variability of the X-ray jets that are formed in the supercritical disk region.     

SS 433 — Again

The standard model for SS 433 encounters increasing difficulties, including geometrical and chemical irregularities, short-time correlations and the presence of circular polarization. It is argued that these difficulties disappear when one drops the assumption that the moving spectral lines are emitted by the (mapped) jets. All the spectral peculiarities can be blamed on (special) radiation from the inner accretion disk, at radius 10⁷ cm, around a young neutron star. The jets consist of relativistic pair plasma-like in all the other jet sources. A prediction is made for the center of the radio jets.     

Nutational effects in SS 433

The nutation effects of an accreting disk around SS 433 are analyzed within the framework of the fully relativistic model of Fang and Ruffini.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.     

Precession instability models of SS433

Several models are available to describe precession instability of SS433: 6- and 7-parameter models, sinusoidal and damped sinusoidal models etc. From the available observation data, it appears that 6- and 7-parameter models are most likely to be incorrect. We have analyzed and compared the sinusoidal and damped sinusoidal models in terms of figures of phase residual, and then proposed and improved a damped sinusoidal model. The data from the three models (sinusoidal, damped sinusoidal, and improved damped sinusoidal model) have been subjected to regression analysis for the purpose of determining the differences among the models.     

VLBA multi-frequency monitoring of SS433

We present results of VLBA observations of SS433 at two epochs at 5, 8.4, and 15 GHz. The AU-scale region of the source is resolved and shows the familiar quasi-symmetric core-jet structures. But at another epoch, the maps show bright knots ejected a few days before the observation, while the core-complex disappeared. The bright jet components are completely depolarised with fractional polarization less than 0.5%. We also present the first VLBI image of SS433 at 22 GHz.     

Circular Polarisation Observations of SS433

We present four epochs of observations of the Galactic X-ray binarySS433 using the Australian Telescope Compact Array (ATCA). These observations, taken on 4 February, 29 February, 23 March and 27 June 2000, at four frequencies ranging from 1–9 Ghz, are used to monitor the circular polarised emission from the source. We obtain circular polarisation spectra for the first three epochs with spectralindices α, (m _c ∝ν ^α), equal to 0.07±0.10, –1.07±0.09 and –0.18±0.05 and also observe a sign change in Stokes V. This change of handedness may indicate along-term restructuring of the magnetic field.     

An interpretation of the SS433 phenomenon

We present a model which provides an interpretation of the observations relating to the object SS433. The model represents the logical development of the proposal of Collins and Newsom (1979) and consists of a binary system comprised of a massive early-type stellar primary, containing a substantial magnetic field and stellar wind, which is precessionally driven with a 165 day period by a much less massive secondary. The cool gas Doppler-shifted spectrum occurs behind a shock front propagating around the system in the remote regions of the stellar magnetic field. The constraints placed on any model by observation are set forth, and particular attention is given to how they are met by this model. Specifically, we show that the energetics and emission requirements are easily met while the observed radial velocity curve can be fit within the mostly stochastic variations displayed by the source. Finally we discuss the implications of the model for further observation and for the immediate past and future of the object.Supported in part by the National Science Foundation.     

The Supercritical Accretion Disk of SS 433

The structure of the SS 433 supercritical accretion disk derived from spectral and photometric data is described. In the disk plane, gas outflows at a velocity of about 100-150 km/s, while above the disk plane, the velocity increases sharply and reaches 1500 km/s at polar angle 60°. The outer parts of the accretion disk are involved in the precessional motion, which means that the slaved disk precession model is correct. There is complex periodic variability in the radial velocities of SS 433. Apart from the well-known precessional and orbital variability, the strongest cycle is 1/7 of the precession period, P7 = 23.228 ± 0.005 days. This is interpreted as evidence for a spiral shock in the accretion disk. The He II 4686 line consists of two components: a stream-formed narrow Gaussian profile and a broad double-peaked one. The latter is completely eclipsed at phase 0.0. Its blue and red peaks are probably emitted in gaseous cocoons around the bases of the relativistic jets. A correct value of the mass function has been found, which shows that the optical star is massive. The relativistic star's mass is estimated to be Mx 6M.     

On the Binary Nature of SS 433

We present time–resolved optical spectroscopy of the famous X-ray binary SS 433. We obtained 61 medium resolution spectra spread over three months and thus cover roughly five orbits and about half a precession phase. We used various emission lines, that we attribute to the accretion disc, to determine the radial velocities of the compact component. They are of course modulated with the orbital period but in addition show a variation of the system velocity on a longer time scale. With the present data it is not possible to determine whether this is a transient effect or a periodic variation, although we present various possible interpretations of this effect.     

Relativistic dispersion effects on SS433 jets

We here investigate the dispersion properties of radiation in the SS433 relativistic jets. We assume that the jet is composed of cold electron-proton plasma immersed in a predominantly parallel magnetic field to the jet axis. We find that for the mildly relativistic source SS433 (for which 〈ψ〉≃79°), the bulk velocity is too small (v≃0.26c) to produce significant changes in the dispersion properties of the medium. Nonetheless, in the rarefied outer regions of the jets, where radio emission dominates, even a weak magnetic field has some influence on the dispersion properties and there appear two different electromagnetic branches that are slightly sensitive to the bulk relativistic motion. In the inner, X-ray region, the magnetic field is much stronger, but in this region the high electron density preserves the isotropic character of the local plasma and no branch separation occurs. In the region of the jet where the IR and optical emission dominates, the cold plasma may be also considered isotropic, i.e., neither the magnetic field nor the bulk velocity is able to affect the propagation of the radiation. Finally, we find that the Doppler line displacement in SS433 is affected by plasma dispersion only in a narrow frequency range in the far IR. As a consequence, although the shift (z) modulation due to precession of the SS433 jets is well described by previous work, it has to be corrected by plasma dispersion effects in the far-IR range.     

Gamma-ray absorption in the microquasar SS433

We discuss the gamma-ray absorption in the inner region of the microquasar SS433. Our investigation includes several contributions to the opacity of this system. They result from the ambient fields generated by the primary star, possibly an A-type supergiant, and a very extended disk around the black hole. Besides the sharp and dramatic absorption effect that occurs every time the star crosses the emission zone, we find in the UV photon field from the extended disk an important source of absorption for very high energy gamma-rays. This results in periodic gamma-ray observational signatures.     

Superbroad component in emission lines of SS 433

We have detected new components in stationary emission lines of SS 433; these are the superbroad components that are low-contrast substrates with a width of 2000–2500 km s^?1 in He I λ4922 and Hβ and 4000–5000 kms^?1 in He II λ4686. Based on 44 spectra taken during four years of observations from 2003 to 2007, we have found that these components in the He II and He I lines are eclipsed by the donor star; their behavior with precessional and orbital phases is regular and similar to the behavior of the optical brightness of SS 433. The same component in Hβ shows neither eclipses nor precessional variability. We conclude that the superbroad components in the helium and hydrogen lines are different in origin. Electron scattering is shown to reproduce well the superbroad component of Hβ at a gas temperature of 20–35 kK and an optical depth for Thomson scattering τ ≈ 0.25?0.35. The superbroad components of the helium lines are probably formed in the wind from the supercritical accretion disk. We have computed a wind model based on the concept of Shakura-Sunyaev supercritical disk accretion. The main patterns of the He II line profiles are well reproduced in this model: not only the appearance of the superbroad component but also the evolution of the central two-component part of the profile of this line during its eclipse by the donor star can be explained.     

Analysis of Multicolor Photometric Observations of SS 433

Observations of the rapid photometric variability of SS 433 in the BVR bands, obtained on Mt. Maidanak during 12 nights in 1989-90, are presented. The behavior of the U - B, B - V, and V - R color indices is analyzed on the basis of multicolor photoelectric observations. It is found that, both for rapid variability during a night and for variability on the scale of the orbital period, color-brightness relations exist for U-(U - B) and B-(B - V), analogous to the well-known V-(V - R) relation, with a characteristic property: the color indices decrease with increasing brightness. It is shown that the object's reddening upon a brightness decrease is not due only to eclipses. The behavior of the color characteristics can be explained by the interaction of the relativistic jets with the atmosphere around the accretion disk.     

An estimate of the effects of light travel times in the optical jets of SS433

The effect of the finite extent of the optically radiating region of SS433 is investigated. Light travel time effects are small, but a slightly improved fit to the observational data can be obtained with a dimension ofl _o?10¹⁵ cm for the optical jets.     

A supercritical accretion disk model for SS 433

We describe a model for SS 433 based on an accretion disk around a black hole. Due to the very high mass transfer rate in the system, the disk must be geometrically thick. Two narrow funnels are formed around the rotation axis and radiation pressure in the funnels accelerates matter to relativistic velocities in the form of two opposite jets. TheX and optical luminosities are evaluated and they agree well with the experimental data.