945 research outputs found
The mass of X-Ray Nova Scorpii 1994 (=GRO J1655--40)]
We have obtained high and intermediate resolution optical spectra of the
black-hole candidate Nova Sco 1994 in May/June 1998, when the source was in
complete (X-ray) quiescence. We measure the radial velocity curve of the
secondary star and obtain a semi-amplitude of K_2=215.5+/-2.4 km/s, which is 6
per cent lower than the only previously determined value. This new value for
K_2 thus reduces the binary mass function to f(M) = 2.73+/-0.09 Mo. Using only
the high resolution spectra we constrain the rotational broadening of the
secondary star, vsini, to lie in the range 82.9-94.9 km/s (95 per cent
confidence) and thus constrain the binary mass ratio to lie in the range
0.337--0.436 (95 per cent confidence). We can also combine our results with
published limits for the binary inclination to constrain the mass of the
compact object and secondary star to the ranges 5.5 -- 7.9 and 1.7 -- 3.3 Mo
respectively (95 per cent confidence). Finally, we report on the detection of
the Lithium resonance line at 6707.8 A, with an equivalent width of 55+/-8 mA.Comment: 5 pages, 5 figures, accepted by MNRA
Hard X-ray lags in GRO J1719-24
We have used the Fourier cross spectra of GRO J1719-24, as obtained with
BATSE, to estimate the phase lags between the X-ray flux variations in the
20--50 and 50--100 keV energy bands as a function of Fourier frequency in the
interval 0.002--0.488 Hz. Our analysis covers the entire ~80 day X-ray outburst
of this black-hole candidate, following the first X-ray detection on 1993
September 25. The X-ray variations in the 50--100 keV band lag those in the
20--50 keV energy band by an approximately constant phase difference of 0.072
+/- 0.010 rad in the frequency interval 0.02--0.20 Hz. The peak phase lags in
the interval 0.02--0.20 Hz are about twice those of Cyg X-1 and GRO
J0422+32.These results are consistent with models for Comptonization regions
composed of extended non-uniform clouds around the central source.Comment: 10 pages, including 4 postscript figures, AASTEX. Accepted for
publication by Ap
Hard X-ray variability of the black-hole candidate GRO J0422+32 during its 1992 outburst
We have studied the hard X-ray variability of the soft X-ray transient GRO
J0422+32 with BATSE in the 20-100 keV energy band. Our analysis covers 180 days
following the first X-ray detection of the source on 1992 August 5, fully
covering its primary and secondary X-ray outburst. We computed power density
spectra (PDSs) in the 20-50, 50-100, and 20-100 keV energy bands, in the
frequency interval 0.002-0.488 Hz. The PDSs of GRO J0422+32 are approximately
flat up to a break frequency, and decay as a power law above, with index ~1.
The canonical anticorrelation between the break frequency and the power density
at the break, observed in Cyg X-1 and other BHCs in the low state, is not
observed in the PDSs of GRO J0422+32. We compare our results with those of
similar variability studies of Cyg X-1. The relation between the spectral slope
and the amplitude of the X-ray variations of GRO J0422+32 is similar to that of
Cyg X-1; however, the relation between the hard X-ray flux and the amplitude of
its variation is opposite to what has been found in Cyg X-1. Phase lags between
the X-ray flux variations of GRO J0422+32 at high and low photon energies,
could only be derived during the first 30 days of its outburst. During this
period, the variations in the 50-100 keV lag those in the 20-50 keV energy band
by an approximately constant phase difference of 0.039(3) rad in the frequency
interval 0.02-0.20 Hz.Comment: 33 pages, including 14 postscript figures, AASTEX. To appear in ApJ
1999, March 1, vol. 513 #
A Magnetic Monopole in Pure SU(2) Gauge Theory
The magnetic monopole in euclidean pure SU(2) gauge theory is investigated
using a background field method on the lattice.
With Monte Carlo methods we study the mass of the monopole in the full
quantum theory.
The monopole background under the quantum fluctuations is induced by imposing
fixed monopole boundary conditions on the walls of a finite lattice volume.
By varying the gauge coupling it is possible to study monopoles with scales
from the hadronic scale up to high energies.
The results for the monopole mass are consistent with a conjecture we made
previously in a realization of the dual superconductor hypothesis of
confinement.Comment: 33 pages uufiles-compressed PostScript including (all) 12 figures,
preprint numbers ITFA-93-19 (Amsterdam), OUTP-93-21P (Oxford), DFTUZ/93/23
(Zaragoza
Correlation Between BATSE Hard X-ray Spectral and Timing Properties of Cygnus X-1
We have analyzed approximately 1100 days of Cygnus X-1 hard X-ray data
obtained with BATSE to study its rapid variability. We find for the first time
correlations between the slope of the spectrum and the hard X-ray intensity,
and between the spectral slope and the amplitude of the rapid variations of the
hard X-ray flux. We compare our results with expectations from current theories
of accretion onto black holes.Comment: 17 pages, 3 Postscript figures, uses aasms4.sty. Accepted for
publication in Astrophysical Journal Letter
Drug-induced atrial fibrillation
Atrial fibrillation (AF) is the most common sustained rhythm disorder observed in clinical practice and predominantly associated with cardiovascular disorders such as coronary heart disease and hypertension. However, several classes of drugs may induce AF in patients without apparent heart disease or may precipitate the onset of AF in patients with preexisting heart disease. We reviewed the literature on drug-induced AF, using the PubMed/Medline and Micromedex databases and lateral references. Successively, we discuss the potential role in the onset of AF of cardiovascular drugs, respiratory system drugs, cytostatics, central nervous system drugs, genitourinary system drugs, and some miscellaneous agents. Drug-induced AF may play a role in only a minority of the patients presenting with AF. Nevertheless, it is important to recognize drugs or other agents as a potential cause, especially in the elderly, because increasing age is associated with multiple drug use and a high incidence of AF. This may contribute to timely diagnosis and management of drug-induced AF
The cross-cultural generalizability of the theory of planned behavior: A study on jobseeking in the Netherlands
Contains fulltext :
56134_aut.pdf (author's version ) (Open Access)
Contains fulltext :
56134_pub.pdf (publisher's version ) (Closed access)9 p
Correlations in Quasi-Periodic Oscillation and Noise Frequencies Among Neutron-Star and Black-Hole X-ray Binaries
We study systematically the ~0.1-1200 Hz quasi-periodic oscillations (QPOs)
and broad noise components observed in the power spectra of non-pulsing
neutron-star and black-hole low-mass X-ray binaries. We show that among these
components we can identify two, occurring over a wide range of source types and
luminosities, whose frequencies follow a tight correlation. The variability
components involved in this correlation include neutron-star kilohertz QPOs and
horizontal-branch oscillations, as well as black-hole QPOs and noise
components. Our results suggest that the same types of variability may occur in
both neutron-star and black-hole systems over three orders of magnitude in
frequency and with coherences that vary widely but systematically. Confirmation
of this hypothesis will strongly constrain theoretical models of these
phenomena and provide additional clues to understanding their nature.Comment: 15 pages, 2 figures (one color figure), to appear in the
Astrophysical Journa
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