X-ray line formation in the spectrum of SS 433

The mechanisms for the formation of X-ray lines in the spectrum of SS 433 are investigated by taking into account the radiative transfer inside the jets. The results ofMonte Carlo numerical simulations are presented. The effect of a decrease in line intensity due to scattering inside the jet turns out to be pronounced, but it does not exceed 60% in magnitude on the entire grid of parameters. The line broadening due to scattering, nutational motion, and the contribution of satellites can lead to overestimates of the jet opening angle ?? from the line widths in Chandra X-ray observations. The fine structure of the lines turns out to be very sensitive to the scattering effects. This makes its investigation by planned X-ray observatories equipped with high-resolution spectrometers (primarily Astro-H) a powerful tool for diagnosing the parameters of the jets in SS 433.     

Colliding winds in symbiotics

The results of gasdynamic modeling allowed us to propose the new mechanism of transition to active state in classical symbiotics and explain the step-by-step rise to the light maximum during the outburst. Good agreement with available observational data for Z And supports our model. Existing observations of symbiotic stars indicate the presence of winds from both components at active stages in these systems. We have carried out the gasdynamic modeling of the outburst development process in the classic symbiotic star Z And in the framework of the colliding winds model. It is shown that contribution from the system of shocks that forms in the area of wind collision is rather significant especially at short wavelengths.     

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.     

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.     

Colliding winds in V1016 Cygni

We present MERLIN observations of the symbiotic nova V1016 Cygni made at 6 cm between 1992 and 1997 and at 18 cm in 1993 and 1997. In the 6-cm images we find complex structure which has not been previously seen, in particular three bright components. These components do not appear to be expanding as would be expected from the remains of a hot wind resulting from the nova outburst. The change in positions of two of the features exhibits tentative east–west movement. The brightness temperature of the peak with the highest flux density remains above 50 000 K in all epochs, thereby confirming the presence of shocked material in the system. At 18 cm there is no evidence of any non-thermal emission as might be expected from comparison with a sister star, HM Sge.     

Peculiar nature of hard X-ray eclipse in SS433 from INTEGRAL observations

The analysis of hard X-ray INTEGRAL observations (2003–2008) of superaccreting Galactic microquasar SS433 at precessional phases of the source with the maximum disc opening angle is carried out. It is found that the shape and width of the primary X-ray eclipse are strongly variable, suggesting additional absorption in dense stellar wind and gas outflows from the optical A7I component and the wind–wind collision region. The independence of the observed hard X-ray spectrum on the accretion disc precessional phase suggests that hard X-ray emission (20–100 keV) is formed in an extended, hot, quasi-isothermal corona, probably heated by interaction of relativistic jet with inhomogeneous wind outflow from the precessing supercritical accretion disc. A joint modelling of X-ray eclipsing and precessional hard X-ray variability of SS433 revealed by INTEGRAL by a geometrical model suggests the binary mass ratio   q = m_x / m _v ≃  0.25–0.5. The absolute minimum of joint orbital and precessional  χ²  residuals is reached at   q ≃ 0.3  . The found binary mass ratio range allows us to explain the substantial precessional variability of the minimum brightness at the middle of the primary optical eclipse. For the mass function of the optical star   f _v = 0.268 M_⊙  as derived from Hillwig & Gies data, the obtained value of   q ≃ 0.3  yields the masses of the components   m_x ≃ 5.3 M_⊙, m _v ≃ 17.7 M_⊙  , confirming the black hole nature of the compact object in SS433.     

Monte Carlo simulations of the broad-band X-ray continuum of SS433

We develop a Monte Carlo technique based on L.B. Lucy's indivisible photon packets method to calculate X-ray continuum spectra of Comptonized thermal plasma in arbitrary geometry and apply it to describe the broad-band X-ray continuum of the galactic superaccreting microquasar SS433 observed by INTEGRAL . A physical model of the X-ray emitting region is proposed that includes thermal emission from the accretion disc, jets and hot corona where the photons of different origin are Comptonized. From comparison with INTEGRAL observations, we estimate physical parameters of the complex X-ray emitting region in SS433 and present model spectra for different viewing angles of the object.     

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.     

Colliding stellar winds in WR+O binary systems

Two-dimensional calculations in the model of two colliding stellar winds are provided. The effects of energy losses on free-free emission and Comptonization are investigated. The expected X-ray emission of a typical WR+O binary system is calculated.     

Identification of X-ray lines in the spectrum of the arcsec-scale precessing jets of SS 433

The extended X-ray emission observed at arcsec scales along the propagation trajectory of the precessing relativistic jets of the Galactic microquasar SS 433 features a broad emission line, with the position of the centroid being significantly different for the approaching and receding jets (≈7.3 and ≈6.4 keV, respectively). These observed line positions are at odds with the predictions of the kinematic model for any of the plausible bright spectral lines in this band, raising the question of their identification. Here we address this issue by taking into account time delays of the emission coming from the receding regions of the jets relative to that from the approaching ones, which cause a substantial phase shift and distortion of the predicted line positions for the extended (~10¹⁷ cm) emission compared to the X-ray and optical lines observed from the central source (emitted at distances ~10¹¹ and ~10¹⁵ cm, respectively). We demonstrate that the observed line positions are fully consistent with the Fe XXVI Lyα (E ₀ = 6.96 keV) line emerging from a region of size ~6 × 10¹⁶ cm along the jet. This supports the idea that intensive reheating of the jets up to temperatures >10 keV takes place at these distances, probably as a result of partial deceleration of the jets due to interaction with the surrounding medium, which might cause collisions between discrete dense blobs inside the jets.     

Fast optical variability of SS 433

We study the variability of the optical flux from the peculiar Galactic source SS 433 based on observations with the Russian-Turkish 1.5-m telescope. We describe in detail the technique of highquality photometric measurements with a time resolution of 0.3–1 s using an ordinary CCD. Through test observations of nonvariable stars, we show that atmospheric turbulence introduces no significant distortions into the light curves. Therefore, such data are well suited for studying the aperiodic variability of various objects.     

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.     

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.