5,656 research outputs found
SS 433 : a phenomenon imitating a Wolf-Rayet star
We present mid-infrared (2-12 micron) spectra of the microquasar SS 433
obtained with the Infrared Space Observatory (spectroscopic mode of ISOPHOT and
ISOCAM). We compare them to the spectra of four Wolf-Rayet stars: WR78, WR134,
WR136, and WR147 in the same wavelength range. The mid-infrared spectrum of SS
433 mainly shows HI and HeI emission lines and is very similar to the spectrum
of WR147, a WN8(h)+B0.5V binary. The 2-12 micron continuum emission of SS 433
corresponds to optically thin and partially optically thick free-free emission,
from which we calculate a mass loss rate of 2-3 x 10^{-4} Msun/yr if the wind
is homogeneous and a third of these values if it is clumped. This is consistent
with a strong stellar wind from a WN star. However, following recent studies
concluding that the mass donor star of SS 433 is not a Wolf-Rayet star, we
propose that this strong wind out flows from a geometrically thick envelope of
material that surrounds the compact object like a stellar atmosphere, imitating
the Wolf-Rayet phenomenon. This wind could also wrap the mass donor star, and
at larger distances (~ 40 AU), it might form a dust envelope from which the
thermal emission, detected with ISOPHOT at 25 micron and 60 micron, would
originate. This wind also probably feeds the material that is ejected in the
orbital plane of the binary system and that forms the equatorial outflow
detected in radio at distances > 100 AU.Comment: 12 pages, 6 figures (3 colour figures), accepted by A&A (in press
Identification of the Mass Donor Star's Spectrum in SS 433
We present spectroscopy of the microquasar SS 433 obtained near primary
eclipse and disk precessional phase Psi = 0.0, when the accretion disk is
expected to be most ``face-on''. The likelihood of observing the spectrum of
the mass donor is maximized at this combination of orbital and precessional
phases since the donor is in the foreground and above the extended disk
believed to be present in the system. The spectra were obtained over four
different runs centered on these special phases. The blue spectra show clear
evidence of absorption features consistent with a classification of A3-7 I. The
behavior of the observed lines indicates an origin in the mass donor. The
observed radial velocity variations are in anti-phase to the disk, the
absorption lines strengthen at mid-eclipse when the donor star is expected to
contribute its maximum percentage of the total flux, and the line widths are
consistent with lines created in an A supergiant photosphere. We discuss and
cast doubt on the possibility that these lines represent a shell spectrum
rather than the mass donor itself. We re-evaluate the mass ratio of the system
and derive masses of 10.9 +/- 3.1 Msun and 2.9 +/- 0.7 Msun for the mass donor
and compact object plus disk, respectively. We suggest that the compact object
is a low mass black hole.
In addition, we review the behavior of the observed emission lines from both
the disk/wind and high velocity jets.Comment: submitted to ApJ, 24 pages, 7 figure
On the Origin of the Absorption Features in SS433
We present high-resolution optical spectroscopy of the X-ray binary system
SS433, obtained over a wide range of orbital phases. The spectra display
numerous weak absorption features, and include the clearest example seen to
date of those features, resembling a mid-A type supergiant spectrum, that have
previously been associated with the mass donor star. However, the new data
preclude the hypothesis that these features originate solely within the
photosphere of the putative mass donor, indicating that there may be more than
one region within the system producing an A supergiant-like spectrum, probably
an accretion disc wind. Indeed, whilst we cannot confirm the possibility that
the companion star is visible at certain phase combinations, it is possible
that all supergiant-like features observed thus far are produced solely in a
wind. We conclude that great care must be taken when interpreting the behaviour
of these weak features.Comment: Accepted for publication in MNRAS, 8 pages, 6 figure
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
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On the putative class of B[e] X-ray binaries
We discuss the putative class of B[e] X-ray binaries, with reference to currently identified candidate systems, focusing on CI Cam and the newly identified class of highly obscured hard X-ray sources detected by INTEGRAL. We suggest that such a class will likely consist of two types of object in which the B[e] phenomenon is (i) intrinsic to the mass donor or (ii) a result of binarity. Finally, we discuss the difficulties inherent in observing B[e] X-ray binaries and the physical motivations for their study, which include the origin of the Galactic hard X-ray emission and the propagation of jets in dense media
Cygnus X-3 and the problem of the missing Wolf-Rayet X-ray binaries
Cygnus X-3 is a strong X-ray source (L_X about 10^38 erg/s) which is thought
to consist of a compact object, accreting matter from a helium star. We find
analytically that the estimated ranges of mass-loss rate and orbital-period
derivative for Cyg X-3 are consistent with two models: i) the system is
detached and the mass loss from the system comes from the stellar wind of a
massive helium star, of which only a fraction that allows for the observed
X-ray luminosity is accreted, or ii) the system is semidetached and a
Roche-lobe-overflowing low- or moderate-mass helium donor transfers mass to the
compact object, followed by ejection of its excess over the Eddington rate from
the system. These analytical results appear to be consistent with evolutionary
calculations. By means of population synthesis we find that currently in the
Galaxy there may exist ~1 X-ray binary with a black hole that accretes from a
>~ 7 MSun Wolf-Rayet star and ~1 X-ray binary in which a neutron star accretes
matter from a Roche-lobe-overflowing helium star with mass <~ 1.5 MSun. Cyg X-3
is probably one of these systems.Comment: 12 pages, 6 figures, accepted by A&
On the Nature of the Compact Object in SS~433. Observational Evidence of X-ray Photon Index Saturation
We present an analysis of the X-ray spectral properties observed from black
hole candidate (BHC) binary SS~433. We have analyzed RXTE data from this
source, coordinated with Green Bank Interferometer/RATAN-600. We show that
SS~433 undergoes a X-ray spectral transition from the low hard state (LHS) to
the intermediate state (IS). We show that the X-ray broad-band energy spectra
during all spectral states are well fit by a sum of so called ``Bulk Motion
Comptonization (BMC) component'' and by two (broad and narrow) Gaussians for
the continuum and line emissions respectively. In addition to these spectral
model components we also find a strong feature that we identify as a
"blackbody-like (BB)" component which color temperature is in the range of 4-5
keV in 24 IS spectra during the radio outburst decay in SS~433. Our
observational results on the "high temperature BB" bump leads us to suggest the
presence of gravitationally redshifted annihilation line emission in this
source. I\ We have also established the photon index saturation at about 2.3 in
index vs mass accretion correlation. This index-mass accretion correlation
allows us to evaluate the low limit of black hole (BH) mass of compact object
in SS~433, M_{bh}> 2 solar masses, using the scaling method using BHC GX 339-4
as a reference source. Our estimate of the BH mass in SS 433 is consistent with
recent BH mass measurement using the radial-velocity measurements of the binary
system by Hillwig & Gies who find that M_{x}=(4.3+/-0.8 solar masses. This is
the smallest BH mass found up to now among all BH sources. Moreover, the index
saturation effect versus mass accretion rate revealed in SS~433, like in a
number of other BH candidates, is the strong observational evidence for the
presence of a BH in SS~433.Comment: 29 pages, 14 figures. Accepted for the ApJ, 2010, October 1, v. 721
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