95 research outputs found
The column density towards LMC X-1
We measure the neutral absorption towards the black hole X-ray binary system
LMC X-1 from six archival soft X-ray spectra obtained with the gratings and/or
CCD detectors on Chandra, XMM-Newton, and Swift. Four spectral models for the
soft continuum have been investigated. While the powerlaw model may
overestimate NH considerably, the others give consistent results. Taking the
lower metalicity of the Large Magellanic Cloud into account, we find equivalent
hydrogen column densities of N_H = (1.0-1.3)*10^22 cm^-2, with a systematic
dependence on the orbital phase. This variation of the neutral absorption can
nearly explain the orbital modulation of the soft X-ray flux recently detected
with the All Sky Monitor (ASM) on the Rossi X-ray Timing Explorer (RXTE).Comment: 4 pages, accepted for publication as a Letter in Astronomy and
Astrophysic
Spectroscopy of the stellar wind in the Cygnus X-1 system
The X-ray luminosity of black holes is produced through the accretion of
material from their companion stars. Depending on the mass of the donor star,
accretion of the material falling onto the black hole through the inner
Lagrange point of the system or accretion by the strong stellar wind can occur.
Cygnus X-1 is a high mass X-ray binary system, where the black hole is powered
by accretion of the stellar wind of its supergiant companion star HDE226868. As
the companion is close to filling its Roche lobe, the wind is not symmetric,
but strongly focused towards the black hole. Chandra-HETGS observations allow
for an investigation of this focused stellar wind, which is essential to
understand the physics of the accretion flow. We compare observations at the
distinct orbital phases of 0.0, 0.2, 0.5 and 0.75. These correspond to
different lines of sights towards the source, allowing us to probe the
structure and the dynamics of the wind.Comment: conference proceeding from Integral/Bart Workshop Karlsbad, CZ,
14.4-18.4 201
A new method for an objective, -based spectroscopic analysis of early-type stars
A precise quantitative spectral analysis - encompassing atmospheric parameter
and chemical elemental abundance determination - is time consuming due to its
iterative nature and the multi-parameter space to be explored, especially when
done "by eye". A robust automated fitting technique that is as trustworthy as
traditional methods would allow for large samples of stars to be analyzed in a
consistent manner in reasonable time. We present a semi-automated quantitative
spectral analysis technique for early-type stars based on the concept of
minimization. The method's main features are: far less subjective than
typical "by eye" methods, correction for inaccurate continuum normalization,
consideration of the whole useful spectral range, simultaneous sampling of the
entire multi-parameter space (effective temperature, surface gravity,
microturbulence, macroturbulence, projected rotational velocity, radial
velocity, elemental abundances) to find the global best solution, applicable
also to composite spectra. The method is fast, robust and reliable as seen from
formal tests and from a comparison with previous analyses. Consistent
quantitative spectral analyses of large samples of early-type stars can be
performed quickly with very high accuracy.Comment: 32 pages, 4 figures, Astronomy and Astrophysics, accepte
Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system. I. The non-dip spectrum in the low/hard state
We present analyses of a 50 ks observation of the supergiant X-ray binary
system Cygnus X-1/HDE 226868 taken with the Chandra High Energy Transmission
Grating Spectrometer (HETGS). Cyg X-1 was in its spectrally hard state and the
observation was performed during superior conjunction of the black hole,
allowing for the spectroscopic analysis of the accreted stellar wind along the
line of sight. A significant part of the observation covers X-ray dips as
commonly observed for Cyg X-1 at this orbital phase, however, here we only
analyze the high count rate non-dip spectrum. The full 0.5-10 keV continuum can
be described by a single model consisting of a disk, a narrow and a
relativistically broadened Fe Kalpha line, and a power law component, which is
consistent with simultaneous RXTE broad band data. We detect absorption edges
from overabundant neutral O, Ne and Fe, and absorption line series from highly
ionized ions and infer column densities and Doppler shifts. With emission lines
of He-like Mg XI, we detect two plasma components with velocities and densities
consistent with the base of the spherical wind and a focused wind. A simple
simulation of the photoionization zone suggests that large parts of the
spherical wind outside of the focused stream are completely ionized, which is
consistent with the low velocities (<200 km/s) observed in the absorption
lines, as the position of absorbers in a spherical wind at low projected
velocity is well constrained. Our observations provide input for models that
couple the wind activity of HDE 226868 to the properties of the accretion flow
onto the black hole.Comment: 16 pages, 15 figures, uses emulateapj, published as ApJ 690:330-346,
2009 January
Übertragbarkeit des Bottom-Up Wirkungsanalyse-Modells auf andere Bedarfsfelder : Arbeitsschritt 6.2 ; Paper zu Arbeitspaket 6 des Projekts "Materialeffizienz und Ressourcenschonung" (MaRess)
Post-history and postmodernity. Two key philosophical concepts of critical culture and of contemporary analysis of media and of technical images by Vilém Flusser
Vilém Flusser´s well-known concept of pós-história (post-history), used for the first time in 1967 and benaming a book from 1982, is not identical with postmodernity, the concept developed by Jean-François Lyotard in 1979, that became quite popular in the early eighties. Nevertheless, after visiting the inaugural exposition of the Centre Pompidou in Paris in 1985 on new technologies, organized by Lyotard, Flusser integrated the concept of postmodernity into his theory. The three published articles on the topic did not receive propper attention. The relevance for communication theory is also provided by the fact that Lyotard´s exhibition, as an underlying structure, made use of Lasswell´s famous formula (Who says what in which channel to whom with what effect?). This enriches Flusser´s reflections on new technologies by an additional aspect
Multi-Satellite Observations of Cygnus X-1 to Study the Focused Wind and Absorption Dips
High-mass X-ray binary systems are powered by the stellar wind of their donor
stars. The X-ray state of Cygnus X-1 is correlated with the properties of the
wind which defines the environment of mass accretion. Chandra-HETGS
observations close to orbital phase 0 allow for an analysis of the photoionzed
stellar wind at high resolution, but because of the strong variability due to
soft X-ray absorption dips, simultaneous multi-satellite observations are
required to track and understand the continuum, too. Besides an earlier joint
Chandra and RXTE observation, we present first results from a recent campaign
which represents the best broad-band spectrum of Cyg X-1 ever achieved: On 2008
April 18/19 we observed this source with XMM-Newton, Chandra, Suzaku, RXTE,
INTEGRAL, Swift, and AGILE in X- and gamma-rays, as well as with VLA in the
radio. After superior conjunction of the black hole, we detect soft X-ray
absorption dips likely due to clumps in the focused wind covering >95 % of the
X-ray source, with column densities likely to be of several 10^23 cm^-2, which
also affect photon energies above 20 keV via Compton scattering.Comment: 10 pages, contributed talk at the 7th Microquasar Workshop, Foca,
Turkey, Sept. 1-5, 200
Confirmation Via the Continuum-Fitting Method that the Spin of the Black Hole in Cygnus X-1 is Extreme
In Gou et al. (2011), we reported that the black hole primary in the X-ray
binary Cygnus X-1 is a near-extreme Kerr black hole with a spin parameter
a*>0.95(3{\sigma}). We confirm this result while setting a new and more
stringent limit: a*>0.983 at the 3{\sigma}(99.7%) level of confidence. The
earlier work, which was based on an analysis of all three useful spectra that
were then available, was possibly biased by the presence in these spectra of a
relatively strong Compton power-law component: The fraction of the thermal seed
photons scattered into the power law was f_s=23-31%, while the upper limit for
reliable application of the continuum-fitting method is f_s<25%. We have
subsequently obtained six additional spectra of Cygnus X-1 suitable for the
measurement of spin. Five of these spectra are of high quality with f_s in the
range 10% to 19%, a regime where the continuum-fitting method has been shown to
deliver reliable results. Individually, the six spectra give lower limits on
the spin parameter that range from a*>0.95 to a*>0.98, allowing us to
conservatively conclude that the spin of the black hole is a*>0.983
(3{\sigma}).Comment: 14 pages in emulated ApJ format, including 6 figures and 4 tables,
ApJ in press. Discussion on the pileup effect to our spin measurement is
added, including a subsection and a new figure, to reflect the referee's
comments; the conclusions are unchange
Corona, Jet, and Relativistic Line Models for Suzaku/RXTE/Chandra-HETG Observations of the Cygnus X-1 Hard State
Using Suzaku and the Rossi X-ray Timing Explorer, we have conducted a series
of four simultaneous observations of the galactic black hole candidate Cyg X-1
in what were historically faint and spectrally hard low states. Additionally,
all of these observations occurred near superior conjunction with our line of
sight to the X-ray source passing through the dense phases of the focused wind
from the mass donating secondary. One of our observations was also simultaneous
with observations by the Chandra-High Energy Transmission Grating. These latter
spectra are crucial for revealing the ionized absorption due to the secondary's
focused wind. Such absorption is present and must be accounted for in all four
spectra. These simultaneous data give an unprecedented view of the 0.8-300 keV
spectrum of Cyg X-1, and hence bear upon both corona and X-ray emitting jet
models of black hole hard states. Three models fit the spectra well: coronae
with thermal or mixed thermal/non-thermal electron populations, and jets. All
three models require a soft component that we fit with a low temperature disk
spectrum with an inner radius of only a few tens of GM/c^2. All three models
also agree that the known spectral break at 10\,keV is not solely due to the
presence of reflection, but each gives a different underlying explanation for
the augmentation of this break. Thus whereas all three models require that
there is a relativistically broadened Fe line, the strength and inner radius of
such a line is dependent upon the specific model, {thus making premature
line-based estimates of the black hole spin in the Cyg X-1 system. We look at
the relativistic line in detail, accounting for the narrow Fe emission and
ionized absorption detected by HETG. Although the specific relativistic
parameters of the line are continuum-dependent, none of the broad line fits
allow for an inner disk radius that is >40 GM/c^2.Comment: 22 pages, 16 figures. Uses emulateapj style. Final three tables
inserted as a figure to avoid issues with astro-ph's version of latex
mangling the use of lscape. To be published in the Astrophysical Journal,
January, 201
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