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 $\lambda4922$ and H$\beta$ and 4000--5000 km s-1 in He II $\lambda4686$. 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 H$\beta$ 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 H$\beta$ at a gas temperature of 20--35 kK and an optical depth for Thomson scattering $\tau \approx$ 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.Comment: 17 pages, 13 figures, 2 tables, published in Astronomy Letters, 2013, vol. 39, N 12, pp. 826 - 84

V4641Sgr - Super-Eddington source enshrouded by an extended envelope

An optical spectroscopy of an unusual fast transient V4641 Sgr constrains its mass to 8.7-11.7M_sun (9.6M_sun is the best fit value) and the distance to 7.4--12.3 kpc (Orosz et al. 2001). At this distance the peak flux of 12 Crab in the 2--12 keV energy band, measured by ASM/RXTE, implies the X-ray luminosity exceeding 2-3e39 erg/s, i.e. near or above the Eddington limit for a 9.6M_sun black hole. An optical photometry shows that at the peak of the optical outburst the visual magnitude increased by Delta m_V > 4.7^m relative to the quiescent level and reached m_V < 8.8^m. An assumption that this optical emission is due to irradiated surface of an accretion disk or a companion star with the the black body shape of the spectrum would mean that the bolometric luminosity of the system exceeds L>3e41 erg/s > 300 L_Edd. We argue that the optical data strongly suggest presence of an extended envelope surrounding the source which absorbs primary X-rays flux and reemits it in optical and UV. The data also suggests that this envelope should be optically thin in UV, EUV and soft X-rays. The observed properties of V4641 Sgr at the peak of an optical flare are very similar to those of SS433. This envelope is likely the result of near or super Eddington rate of mass accretion onto the black hole and it vanishes during subsequent evolution of the source when apparent luminosity drops well below the Eddington value. Thus this transient source provides us direct proof of the dramatic change in the character of an accretion flow at the mass accretion rate near or above the critical Eddington value as predicted long time ago by the theoretical models.Comment: 4 pages, 2 figures. Submitted to A&A Letter