135 research outputs found
The Mass of the Black Hole in Cygnus X-1
Cygnus X-1 is a binary star system that is comprised of a black hole and a
massive giant companion star in a tight orbit. Building on our accurate
distance measurement reported in the preceding paper, we first determine the
radius of the companion star, thereby constraining the scale of the binary
system. To obtain a full dynamical model of the binary, we use an extensive
collection of optical photometric and spectroscopic data taken from the
literature. By using all of the available observational constraints, we show
that the orbit is slightly eccentric (both the radial velocity and photometric
data independently confirm this result) and that the companion star rotates
roughly 1.4 times its pseudosynchronous value. We find a black hole mass of M
=14.8\pm1.0 M_{\sun}, a companion mass of M_{opt}=19.2\pm1.9 M_{\sun}, and the
angle of inclination of the orbital plane to our line of sight of i=27.1\pm0.8
deg.Comment: Paper II of three papers on Cygnus X-1; 27 pages including 5 figures
and 3 tables, ApJ in pres
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
The Extreme Spin of the Black Hole in Cygnus X-1
The compact primary in the X-ray binary Cygnus X-1 was the first black hole
to be established via dynamical observations. We have recently determined
accurate values for its mass and distance, and for the orbital inclination
angle of the binary. Building on these results, which are based on our favored
(asynchronous) dynamical model, we have measured the radius of the inner edge
of the black hole's accretion disk by fitting its thermal continuum spectrum to
a fully relativistic model of a thin accretion disk. Assuming that the spin
axis of the black hole is aligned with the orbital angular momentum vector, we
have determined that Cygnus X-1 contains a near-extreme Kerr black hole with a
spin parameter a/M>0.95 (3\sigma). For a less probable (synchronous) dynamical
model, we find a/M>0.92 (3\sigma). In our analysis, we include the
uncertainties in black hole mass, orbital inclination angle and distance, and
we also include the uncertainty in the calibration of the absolute flux via the
Crab. These four sources of uncertainty totally dominate the error budget. The
uncertainties introduced by the thin-disk model we employ are particularly
small in this case given the extreme spin of the black hole and the disk's low
luminosity.Comment: Paper III of three papers on Cygnus X-1; 21 pages including 5 figures
and 12 tables, ApJ in press. The paper is significantly restructured; two
further tests of the robustness of our spin measurement are presented, and
our error analysis has been substantially improved; the conclusions are
unchange
A Dynamical Study of the Black Hole X-ray Binary Nova Muscae 1991
We present a dynamical study of the Galactic black hole binary system Nova
Muscae 1991 (GS/GRS 1124-683). We utilize 72 high resolution Magellan
Echellette (MagE) spectra and 72 strictly simultaneous V-band photometric
observations; the simultaneity is a unique and crucial feature of this
dynamical study. The data were taken on two consecutive nights and cover the
full 10.4-hour orbital cycle. The radial velocities of the secondary star are
determined by cross-correlating the object spectra with the best-match template
spectrum obtained using the same instrument configuration. Based on our
independent analysis of five orders of the echellette spectrum, the
semi-amplitude of the radial velocity of the secondary is measured to be K_2 =
406.8+/-2.7 km/s, which is consistent with previous work, while the uncertainty
is reduced by a factor of 3. The corresponding mass function is f(M) =
3.02+/-0.06 M_\odot. We have also obtained an accurate measurement of the
rotational broadening of the stellar absorption lines (v sin i = 85.0+/-2.6
km/s) and hence the mass ratio of the system q = 0.079+/-0.007. Finally, we
have measured the spectrum of the non-stellar component of emission that veils
the spectrum of the secondary. In a future paper, we will use our
veiling-corrected spectrum of the secondary and accurate values of K_2 and q to
model multi-color light curves and determine the systemic inclination and the
mass of the black hole.Comment: ApJ accepted version; minor revision; added a subsection about
systematic uncertaintie
Tomography of X-ray Nova Muscae 1991: Evidence for ongoing mass transfer and stream-disc overflow
We present a spectroscopic analysis of the black hole binary Nova Muscae 1991
in quiescence using data obtained in 2009 with MagE on the Magellan Clay
telescope and in 2010 with IMACS on the Magellan Baade telescope at the Las
Campanas Observatory. Emission from the disc is observed in H alpha, H beta and
Ca II (8662 A). A prominent hotspot is observed in the Doppler maps of all
three emission lines. The existence of this spot establishes ongoing mass
transfer from the donor star in 2009-2010 and, given its absence in the
1993-1995 observations, demonstrates the presence of a variable hotspot in the
system. We find the radial distance to the hotspot from the black hole to be
consistent with the circularization radius. Our tomograms are suggestive of
stream-disc overflow in the system. We also detect possible Ca II (8662 A)
absorption from the donor star.Comment: 10 pages, 11 figures, 1 table. Accepted for publication in MNRA
The Extreme Spin of the Black Hole in Cygnus X-1
The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observatIOns. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these.results, which are based on our favored (asynchronous) dynamical model, we have measured the radius of the inner edge of the black hole's accretion disk by fitting its thermal continuum.spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-I contains a near-extreme Kerr black hole with a spin parameter a* > 0.95 (3(sigma)). For a less probable (synchronous) dynamIcal model, we find a* > 0.92 (3(sigma)). In our analysis, we include the uncertainties in black hole mass orbital inclination angle and distance, and we also include the uncertainty in the calibration of the absolute flux via the Crab. These four sources of uncertainty totally dominate the error budget. The uncertainties introduced by the thin-disk model we employ are particularly small in this case given the extreme spin of the black hole and the disk's low luminosity
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The Extreme Spin of the Black Hole in Cygnus X-1
The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observations. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these results, which are based on our favored (asynchronous) dynamical model, we have measured the radius of the inner edge of the black hole's accretion disk by fitting its thermal continuum spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-1 contains a near-extreme Kerr black hole with a spin parameter a * > 0.95 (3σ). For a less probable (synchronous) dynamical model, we find a * > 0.92 (3σ). In our analysis, we include the uncertainties in black hole mass, orbital inclination angle, and distance, and we also include the uncertainty in the calibration of the absolute flux via the Crab. These four sources of uncertainty totally dominate the error budget. The uncertainties introduced by the thin-disk model we employ are particularly small in this case given the extreme spin of the black hole and the disk's low luminosity.Astronom
The Trigonometric Parallax of Cygnus X-1
We report a direct and accurate measurement of the distance to the X-ray
binary Cygnus X-1, which contains the first black hole to be discovered. The
distance of 1.86 (-0.11,+0.12) kpc was obtained from a trigonometric parallax
measurement using the Very Long Baseline Array. The position measurements are
also sensitive to the 5.6 d binary orbit and we determine the orbit to be
clockwise on the sky. We also measured the proper motion of Cygnus X-1 which,
when coupled to the distance and Doppler shift, gives the three-dimensional
space motion of the system. When corrected for differential Galactic rotation,
the non-circular (peculiar) motion of the binary is only about 21 km/s,
indicating that the binary did not experience a large "kick" at formation.Comment: Paper I of three papers on Cygnus X-1; 13 pages including 3 figures
and 2 tables, ApJ in pres
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Increasing Safety and Reducing Environmental Damage Risk from Aging High-Level Radioactive Waste Tanks
Cracks of various shapes and sizes exist in large high-level waste (HLW) tanks at several DOE sites. There is justifiable concern that these cracks could grow to become unstable causing a substantial release of liquid contaminants to the environment. Accurate prediction of crack growth behavior in the tanks, especially during accident scenarios, is not possible with existing analysis methodologies. This research project responds to this problem by developing an improved ability to predict crack growth in material structure combinations that are ductile (Fig. 1). This new model not only addresses the problem for these tanks, but also has applicability to any crack in any ductile structure
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