4,521 research outputs found
A comparison of broad iron emission lines in archival data of neutron star low-mass X-ray binaries
Relativistic X-ray disk-lines have been found in multiple neutron star
low-mass X-ray binaries, in close analogy with black holes across the
mass-scale. These lines have tremendous diagnostic power and have been used to
constrain stellar radii and magnetic fields, often finding values that are
consistent with independent timing techniques. Here, we compare CCD-based data
from Suzaku with Fe K line profiles from archival data taken with gas-based
spectrometers. In general, we find good consistency between the gas-based line
profiles from EXOSAT, BeppoSAX and RXTE and the CCD data from Suzaku,
demonstrating that the broad profiles seen are intrinsic to the line and not
broad due to instrumental issues. However, we do find that when fitting with a
Gaussian line profile, the width of the Gaussian can depend on the continuum
model in instruments with low spectral resolution, though when the different
models fit equally well the line widths generally agree. We also demonstrate
that three BeppoSAX observations show evidence for asymmetric lines, with a
relativistic disk-line model providing a significantly better fit than a
Gaussian. We test this by using the posterior predictive p-value method, and
bootstrapping of the spectra to show that such deviations from a Gaussian are
unlikely to be observed by chance.Comment: 13 pages, 9 figures, accepted to Ap
Simultaneous BeppoSAX and RXTE observations of the X-ray burst sources GX 3+1 and Ser X-1
We have obtained spectral and timing data on GX 3+1 and Ser X-1. Both sources
were observed simultaneously with BeppoSAX and RXTE. The RXTE data is used to
provide power spectra and colour-colour diagrams in order to constrain the
state (and thus track ) the sources are in. The BeppoSAX data provide
the broad-band spectra. The spectra of both sources are reasonably well-fit
using a model consisting of a disk-blackbody, a comptonized component and a Fe
line, absorbed by interstellar absorption. The electron temperature (kT) of the Comptonizing plasma is in both cases 2.5 keV. This implies
that no strong high-energy tail from the Comptonized component is present in
either of the sources. We discuss the similarities between these burst sources
and the luminous X-ray sources located in globular clusters. We find that the
spectral parameters of the comptonized component provide information about the
mass-accretion rate, which agrees well with estimates from the timing and
spectral variations.Comment: 8 pages, accepted by A&
A model for upper kHz QPO coherence of accreting neutron star
{We investigate the coherence of the twin kilohertz quasi-periodic
oscillations (kHz QPOs) in the low-mass X-ray binary (LMXB) theoretically. The
profile of upper kHz QPO, interpreted as Keplerian frequency, is ascribed to
the radial extent of the kHz QPO emission region, associated with the
transitional layer at the magnetosphere-disk boundary, which corresponds to the
coherence of upper kHz QPO. The theoretical model for Q-factor of upper kHz QPO
is applied to the observational data of five Atoll and five Z sources, and the
consistence is implied.Comment: accepted by A&
Morphological analysis on the coherence of kHz QPOs
We take the recently published data of twin kHz quasi-period oscillations
(QPOs) in neutron star (NS) lowmass X-ray binaries (LMXBs) as the samples, and
investigate the morphology of the samples, which focuses on the quality factor,
peak frequency of kHz QPOs, and try to infer their physical mechanism. We
notice that: (1) The quality factors of upper kHz QPOs are low (2 ~ 20 in
general) and increase with the kHz QPO peak frequencies for both Z and Atoll
sources. (2) The distribution of quality factor versus frequency for the lower
kHz QPOs are quite different between Z and Atoll sources. For most Z source
samples, the quality factors of lower kHz QPOs are low (usually lower than 15)
and rise steadily with the peak frequencies except for Sco X-1, which drop
abruptly at the frequency of about 750 Hz. While for most Atoll sources, the
quality factors of lower kHz QPOs are very high (from 2 to 200) and usually
have a rising part, a maximum and an abrupt drop. (3) There are three Atoll
sources (4U 1728-34, 4U 1636-53 and 4U 1608-52) of displaying very high quality
factors for lower kHz QPOs. These three sources have been detected with the
spin frequencies and sidebands, in which the source with higher spin frequency
presents higher quality factor of lower kHz QPOs and lower difference between
sideband frequency and lower kHz QPO frequency.Comment: 8 pages, 8 figures, publishe
Radii and Binding Energies of Nuclei in the Alpha-Cluster Model
The alpha-cluster model is based on two assumptions that the proton-neutron
pair interactions are responsible for adherence between alpha-clusters and that
the NN-interaction in the alpha-clusters is isospin independent. It allows one
to estimate the Coulomb energy and the short range inter-cluster bond energy in
dependence on the number of clusters. The charge radii are calculated on the
number of alpha-clusters too. Unlike the Weizsacker formula in this model the
binding energies of alpha-clusters and excess neutrons are estimated
separately. The calculated values are in a good agreement with the experimental
data.Comment: Latex2e 2.09, 13 pages, 4 figure
ON NON-RIEMANNIAN PARALLEL TRANSPORT IN REGGE CALCULUS
We discuss the possibility of incorporating non-Riemannian parallel transport
into Regge calculus. It is shown that every Regge lattice is locally equivalent
to a space of constant curvature. Therefore well known-concepts of differential
geometry imply the definition of an arbitrary linear affine connection on a
Regge lattice.Comment: 12 pages, Plain-TEX, two figures (available from the author
Application of wavelets to singular integral scattering equations
The use of orthonormal wavelet basis functions for solving singular integral
scattering equations is investigated. It is shown that these basis functions
lead to sparse matrix equations which can be solved by iterative techniques.
The scaling properties of wavelets are used to derive an efficient method for
evaluating the singular integrals. The accuracy and efficiency of the wavelet
transforms is demonstrated by solving the two-body T-matrix equation without
partial wave projection. The resulting matrix equation which is characteristic
of multiparticle integral scattering equations is found to provide an efficient
method for obtaining accurate approximate solutions to the integral equation.
These results indicate that wavelet transforms may provide a useful tool for
studying few-body systems.Comment: 11 pages, 4 figure
Commentary: seed bacterial inhabitants and their routes of colonization
Background
Seeds host bacterial inhabitants but only a limited knowledge is available on which taxa inhabit seed, which niches could be colonized, and what the routes of colonization are.
Scope
Within this commentary, a discussion is provided on seed bacterial inhabitants, their taxa, and from where derive the seed colonizers.
Conclusions
Seeds/and grains host specific bacteria deriving from the anthosphere, carposphere, or from cones of gymnosperms and inner tissues of plants after a long colonization from the soil to reproductive organs
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