2,635 research outputs found
Discovery of orbital decay in SMC X-1
The results are reported of three observations of the binary X ray pulsar SMC X-1 with the Ginga satellite. Timing analyses of the 0.71 s X ray pulsations yield Doppler delay curves which, in turn, provide the most accurate determination of the SMC X-1 orbital parameters available to date. The orbital phase of the 3.9 day orbit is determined in May 1987, Aug. 1988, and Aug. 1988 with accuracies of 11, 1, and 3.5 s, respectively. These phases are combined with two previous determinations of the orbital phase to yield the rate of change in the orbital period: P sub orb/P sub orb = (-3.34 + or - 0.023) x 10(exp -6)/yr. An interpretation of this measurement and the known decay rate for the orbit of Cen X-3 is made in the context of tidal evolution. Finally, a discussion is presented of the relation among the stellar evolution, orbital decay, and neutron star spinup time scales for the SMC X-1 system
The Distribution of X-ray Dips with Orbital Phase in Cygnus X-1
We present results of a comprehensive study of the distribution of absorption
dips with orbital phase in Cygnus X-1. Firstly, the distribution was obtained
using archival data from all major X-ray observatories and corrected for the
selection effect that phase zero (superior conjunction of the black hole) has
been preferentially observed. Dip occurrence was seen to vary strongly with
orbital phase \phi, with a peak at \phi ~ 0.95, i.e. was not symmetric about
phase zero. Secondly, the RXTE ASM has provided continuous coverage of the Low
State of Cygnus X-1 since Sept. 1996, and we have selected dip data based on
increases in hardness ratio. The distribution, with much increased numbers of
dip events, confirms that the peak is at \phi ~ 0.95, and we report the
discovery of a second peak at \phi ~ 0.6. We attribute this peak to absorption
in an accretion stream from the companion star HDE 226868. We have estimated
the ionization parameter at different positions showing that radiative
acceleration of the wind is suppressed by photoionization in particular regions
in the binary system. To obtain the variation of column density with phase, we
make estimates of neutral wind density for the extreme cases that acceleration
of the wind is totally suppressed, or not suppressed at all. An accurate
description will lie between these extremes. In each case, a strong variation
of column density with orbital phase resulted, similar to the variation of dip
occurrence. This provides evidence that formation of the blobs in the wind
which lead to absorption dips depends on the density of the neutral component
in the wind, suggesting possible mechanisms for blob growth.Comment: 9 pages, Latex, 7 ps figures. accepted by MNRA
Reactive-site mutants of N-TIMP-3 that selectively inhibit ADAMTS-4 and ADAMTS-5: biological and structural implications.
Published versio
Correlation between X-ray flux and rotational acceleration in Vela X-1
The results of a search for correlations between X-ray flux and angular acceleration for the accreting binary pulsar Vela X-1 are presented. Results are based on data obtained with the Hakucho satellite during the interval 1982 to 1984. In undertaking this correlation analysis, it was necessary to modify the usual statistical method to deal with conditions imposed by generally unavoidable satellite observing constraints, most notably a mismatch in sampling between the two variables. The results are suggestive of a correlation between flux and the absolute value of the angular acceleration, at a significance level of 96 percent. The implications of the methods and results for future observations and analysis are discussed
Microscopic thickness determination of thin graphite films formed on SiC from quantized oscillation in reflectivity of low-energy electrons
Low-energy electron microscopy (LEEM) was used to measure the reflectivity of
low-energy electrons from graphitized SiC(0001). The reflectivity shows
distinct quantized oscillations as a function of the electron energy and
graphite thickness. Conduction bands in thin graphite films form discrete
energy levels whose wave vectors are normal to the surface. Resonance of the
incident electrons with these quantized conduction band states enhances
electrons to transmit through the film into the SiC substrate, resulting in
dips in the reflectivity. The dip positions are well explained using
tight-binding and first-principles calculations. The graphite thickness
distribution can be determined microscopically from LEEM reflectivity
measurements.Comment: 7 pages, 3 figure
Experimental ancilla-assisted qubit transmission against correlated noise using quantum parity checking
We report the experimental demonstration of a transmission scheme of photonic
qubits over unstabilized optical fibers, which has the plug-and-play feature as
well as the ability to transmit any state of a qubit, regardless of whether it
is known, unknown, or entangled to other systems. A high fidelity to the
noiseless quantum channel was achieved by adding an ancilla photon after the
signal photon within the correlation time of the fiber noise and by performing
quantum parity checking. Simplicity, maintenance-free feature and robustness
against path-length mismatches among the nodes make our scheme suitable for
multi-user quantum communication networks.Comment: 8 pages, 4 figures; published in New J. Phys. and selected in IOP
Selec
An X-Ray Dip in the X-Ray Transient 4U 1630-47
An x-ray dip was observed during a 1996 Rossi X-Ray Timing Explorer
observation of the recurrent x-ray transient 4U 1630-47. During the dip, the
2-60 keV x-ray flux drops by a factor of about three, and, at the lowest point
of the dip, the x-ray spectrum is considerably softer than at non-dip times. We
find that the 4U 1630-47 dip is best explained by absorption of the inner part
of an accretion disk, while the outer part of the disk is unaffected. The
spectral evolution during the dip is adequately described by the variation of a
single parameter, the column density obscuring the inner disk.Comment: 13 pages, 4 figures, Accepted for publication in Ap
Spectral properties of the X-ray binary pulsar LMC X-4 during different intensity states
We present spectral variations of the binary X-ray pulsar LMC X-4 observed
with the RXTE/PCA during different phases of its 30.5 day long third period.
Only out of eclipse data were used for this study. The 3-25 keV spectrum,
modeled with high energy cut-off power-law and iron line emission is found to
show strong dependence on the intensity state. Correlations between the Fe line
emission flux and different parameters of the continuum are presented here.Comment: 4 pages, 4 figure
Study of the cyclotron feature in MXB 0656-072
We have monitored a type II outburst of the Be/X-ray binary MXB 0656−072 in a series of pointed RXTE observations during October through December 2003. The source spectrum shows a cyclotron resonance scattering feature at 32.8 +0.5
−0.4 keV, corresponding to a magnetic field strength of 3.67
+0.06 −0.04 × 10 12 G and is stable through the outburst and over the pulsar spin phase. The pulsar, with an average pulse period of 160.4 ± 0.4s,shows a spin-up of 0.45 s over the duration of the outburst. From optical data, the source distance is estimated to be 3.9 ± 0.1 kpc and this is used to estimate the X-ray luminosity and a theoretical prediction of the pulsar spin-up during the outburst
- …