179 research outputs found
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 and H and 4000--5000 km s-1 in
He II . 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 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 at a
gas temperature of 20--35 kK and an optical depth for Thomson scattering 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
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