We present results of optical spectroscopic observations of the mass donor star in SS 433 with Subaru and Gemini, with an aim to best constrain the mass of the compact object. Subaru/FOCAS observations were performed on 4 nights of October 6-8 and 10, 2007, covering the orbital phase of φ = 0.96 − 0.26. We first calculate cross correlation function (CCF) of these spectra with that of the reference star HD 9233 in the wavelength range of 4740-4840 Å. This region is selected to avoid "strong" absorption lines accompanied with contaminating emission components, which most probably originate from the surroundings of the donor star, such as the wind and gas stream. The same analysis is applied to archive data of Gemini/GMOS taken at φ = 0.84 − 0.30 by Hillwig & Gies (2008). From the Subaru and Gemini CCF results, the amplitude of radial velocity curve of the donor star is determined to be 58.3±3.8 km s −1 with a systemic velocity of 59.2±2.5 km s −1 . Together with the radial velocity curve of the compact object, we derive the mass of the donor star and compact object to be M O =12.4±1.9 M ⊙ and M X =4.3±0.6 M ⊙ , respectively. We conclude, however, that these values should be taken as upper limits. From the analysis of the averaged absorption line profiles of strong lines (mostly ions) and weak lines (mostly neutrals) observed with Subaru, we find evidence for heating effects from the compact object. Using a simple model, we find that the true radial velocity amplitude of the donor star could be as low as 40±5 km s −1 in order to produce the observed absorption-line profiles. Taking into account the heating of the donor star may lower the derived masses to M O = 10.4 +2.3 −1.9 M ⊙ and M X = 2.5 +0.7 −0.6 M ⊙ . Our final constraint, 1.9 M ⊙ ≤ M X ≤ 4.9 M ⊙ , indicates that the compact object in SS 433 is most likely a low mass black hole, although the possibility of a massive neutron star cannot be firmly excluded.

We analysed the XMM–Newton spectra of SS 433 using a standard model of adiabatically and radiatively cooling X‐ray jets. The multitemperature thermal jet model reproduces the strongest observed emission line fluxes well. Fitting the He‐ and H‐like iron line fluxes, we find that the visible blue jet base temperature is ∼17 keV, the jet kinetic luminosity Lk∼ 2 × 1039 erg s−1 and the absorbing column density NH∼ 1.5 × 1022 cm−2. All these parameters are in line with previous studies. The thermal model alone cannot reproduce the continuum radiation in the XMM spectral range, nor the fluorescent iron line and some of the broad spectral features. Using the thermal jet‐plus‐reflection model, we find a notable contribution of ionized reflection to the spectrum in the energy range from ∼3 to 12 keV. The reflecting surface is highly ionized (ξ∼ 300), and the illuminating radiation photon index changes from Γ≈ 2 (a flat spectrum) in the range 7–12 keV to Γ≈ 1.6 in the range 4–7 keV, and to Γ≲ 1 in the range 2–4 keV. We conclude that the reflected spectrum is evidence of the supercritical disc funnel, whereby the illuminating radiation comes from deeper funnel regions, to be further reflected in the outer visible funnel walls (r≳ 2 × 1011 cm). In the multiple scatterings in the funnel, the harder radiation >7 keV may survive absorption, but softer radiation is absorbed, making the illuminating spectrum curved. We have not found any evidence of reflection in the soft 0.8–2 keV energy range; instead, a soft excess is detected, which does not depend on the details of the thermal jet model. However, the soft component spectrum is basically unknown. This soft component might prove to be the direct radiation of the visible funnel wall. It is represented here either as blackbody radiation with a temperature of θbb≈ 0.1 keV and a luminosity of Lbb∼ 3 × 1037 erg s−1, or with a multicolour funnel model. The soft spectral component has parameters roughly the same as those found in ultraluminous X‐ray sources.

We study a stochastic variability of SS 433 in the 10 −4 − 5 × 10 −2 Hz frequency range based on RXTE data, and on simultaneous observations with RXTE and optical telescopes. We find that the cross-correlation functions and power spectra depends drastically on the precession phase of the supercritical accretion disc. When the wind funnel of the disc is maximally open to the observer, a flat part emerges in the power spectrum; a break is observed at the frequency 1.7 × 10 −3 Hz, with a power-law index β ≈ 1.67 at higher frequencies. The soft emission forming mostly in the jets, lags behind the hard and optical emission. When the observer does not see the funnel and jets (the 'edge-on' disc), the power spectrum is described by a single power-law with β ≈ 1.34 and no correlations between X-ray ranges are detected. We investigated two mechanisms to explain the observed variability at the open disc phase, 1) reflection of radiation at the funnel wall (X-rays and optical) and 2) the gas cooling in the jets (X-rays only). The X-ray variability is determined by the contribution of both mechanisms, however the contribution of the jets is much higher. We found that the funnel size is (2 − 2.5) × 10 12 cm, and the opening angle is ϑ f ∼ 50 • . X-ray jets may consist of three fractions with different densities: 8 × 10 13 , 3 × 10 13 and 5 × 10 11 cm −3 , with most of the jet's mass falling within the latter fraction. We suppose that revealed flat part in the power spectrum may be related to an abrupt change in the disc structure and viscous time-scale at the spherization radius, because the accretion disc becomes thick at this radius, h/r ∼ 1. The extent of the flat spectrum depends on the variation of viscosity at the spherization radius.

The aim of the present paper is to investigate a possible contribution of the rotationpowered pulsars and pulsar wind nebulae to the population of ultraluminous X-ray sources (ULXs). We first develop an analytical model for the evolution of the distribution function of pulsars over the spin period and find both the steady-state and the time-dependent solutions. Using the recent results on the X-ray efficiency dependence on pulsar characteristic age, we then compute the X-ray luminosity function (XLF) of rotation-powered pulsars. In a general case it has a broken power-law shape with a high luminosity cutoff, which depends on the distributions of the birth spin period and the magnetic field.Using the observed XLF of sources in the nearby galaxies and the condition that the pulsar XLF does not exceed that, we find the allowed region for the parameters describing the birth period distribution. We find that the mean pulsar period should be greater than 10-40 ms. These results are consistent with the constraints obtained from the X-ray luminosity of core-collapse supernovae. We estimate that the contribution of the rotation-powered pulsars to the ULX population is at a level exceeding 3 per cent. For a wide birth period distribution, this fraction grows with luminosity and above 10 40 erg s −1 pulsars can dominate the ULX population.