1,770 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
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The Federal Bureau of Investigation and Terrorism Investigations
This report provides background information on key elements of the FBI terrorism investigative process based on publicly available information. This report sets forth possible considerations for Congress as it executes its oversight role. These issues include the extent to which intelligence has been integrated into FBI operations to support its counterterrorism mission and the progress the Bureau has made on its intelligence reform initiatives
Recommended from our members
The Federal Bureau of Investigation and Terrorism Investigations
This report provides background information on key elements of the FBI terrorism investigative process based on publicly available information. This report sets forth possible considerations for Congress as it executes its oversight role. These issues include the extent to which intelligence has been integrated into FBI operations to support its counterterrorism mission and the progress the Bureau has made on its intelligence reform initiatives. In addition, these issues will also be relevant during confirmation hearings for a new director
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American Jihadist Terrorism: Combating a Complex Threat
Between May 2009 and August 2010, arrests were made for 19 "homegrown," jihadist-inspired terrorist plots by American citizens or legal permanent residents of the United States. The apparent spike in such activity after May 2009 suggests that at least some Americans - even if a tiny minority - continue to be susceptible to ideologies supporting a violent form of jihad. This report describes homegrown violent jihadists and the plots and attacks that have occurred since 9/11. This report also provides official definitions for terms such as "homegrown," "jihadist," and "violent jihadist." The report also discusses the radicalization process and the forces driving violent extremist activity. It analyzes post-9/11 domestic jihadist terrorism, describes law enforcement and intelligence efforts to combat terrorism and the challenges associated with those efforts. It also outlines actions underway to build trust and partnership between community groups and government agencies and the tensions that may occur between law enforcement and engagement activities
Demographic, Behavioral and Perceptual Comparisons of the U.S. Visitor Experience with Group Package Tours and Free Independent Travel to China
U.S. visitor demand for the China travel experience is anticipated to rise significantly through 2105, causing the Chinese government to employ 100 million service providers over the next six years and raising concern about service delivery and perceptions of the on-site China experience. In an effort to better understand these issues concerning U.S. visitors, this study investigated two specific types of U.S. travelers to China: Group Package Tour (GPT) visitors and Free Independent Travel (FIT) visitors. Results indicated that GPT visitors were more likely to be older and have higher household income than FIT visitors. Four trip-related characteristics of GPT and FIT visitors were found to be significantly different, with GPT visitors showing higher levels of satisfaction with the overall China on-site travel experience
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
Urinary ATP and visualization of intracellular bacteria: a superior diagnostic marker for recurrent UTI in renal transplant recipients?
Renal transplant recipients (RTR) are highly susceptible to urinary tract infections (UTIs) with over 50% of patients having at least one UTI within the first year. Yet it is generally acknowledged that there is considerable insensitivity and inaccuracy in routine urinalysis when screening for UTIs. Thus a large number of transplant patients with genuine urine infections may go undiagnosed and develop chronic recalcitrant infections, which can be associated with graft loss and morbidity. Given a recent study demonstrating ATP is released by urothelial cells in response to bacteria exposure, possibly acting at metabotropic P2Y receptors mediating a proinflammatory response, we have investigated alternative, and possibly more appropriate, urinalysis techniques in a cohort of RTRs.Mid-stream urine (MSU) samples were collected from 53 outpatient RTRs. Conventional leukocyte esterase and nitrite dipstick tests, and microscopic pyuria counts (in 1 ?l), ATP concentration measurements, and identification of intracellular bacteria in shed urothelial cells, were performed on fresh unspun samples and compared to ‘gold-standard’ bacterial culture results.Of the 53 RTRs, 22% were deemed to have a UTI by ‘gold-standard’ conventional bacteria culture, whereas 87%, 8% and 4% showed evidence of UTIs according to leukocyte esterase dipstick, nitrite dipstick, and a combination of both dipsticks, respectively. Intracellular bacteria were visualized in shed urothelial cells of 44% of RTRs, however only 1 of the 23 RTRs (44%) was deemed to have a UTI by conventional bacteria culture. A significant association of the ‘gold-standard’ test with urinary ATP concentration combined with visualization of intracellular bacteria in shed urothelial cells was determined using the Fisher’s exact test.It is apparent that standard bedside tests for UTIs give variable results and that seemingly quiescent bacteria in urothelial cells are very common in RTRs and may represent a focus of subclinical infection. Furthermore, our results suggest urinary ATP concentration combined with detection of intracellular bacteria in shed urinary epithelial cells may be a sensitive means by which to detect ‘occult’ infection in RTRs
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