5,845 research outputs found
X-ray study of HLX1: intermediate-mass black hole or foreground neutron star?
We re-assess the XMM-Newton and Swift observations of HLX1, to examine the
evidence for its identification as an intermediate-mass black hole. We show
that the X-ray spectral and timing properties are equally consistent with an
intermediate-mass black hole in a high state, or with a foreground neutron star
with a luminosity of about a few times 10^{32} erg/s ~ 10^{-6} L_{Edd}, located
at a distance of about 1.5 to 3 kpc. Contrary to previously published results,
we find that the X-ray spectral change between the two XMM-Newton observations
of 2004 and 2008 (going from power-law dominated to thermal dominated) is not
associated with a change in the X-ray luminosity. The thermal component becomes
more dominant (and hotter) during the 2009 outburst seen by Swift, but in a way
that is consistent with either scenario.Comment: 10 pages, accepted by MNRAS. Corrected LZ's affiliation and updated 1
referenc
The end of fertility: age, fecundity and fecundability in women
Onset of capacity for childbearing in women is dated biologically by menarche, although actual onset may be delayed. The end of childbearing is less understood but recent demographic and biological research on fertility at older ages is clarifying the end of fertility. The demographic view of declining fertility with age is based on age-specific fertility in natural fertility populations, artificial insemination and pregnancy rates by age and World Fertility Survey data. New data from the Demographic and Health Surveys on exposure to the risk of pregnancy shows that whereas older women biologically need longer exposure to pregnancy, exposure declines on behavioural grounds such as duration of marriage. Actual fecundity is obscured by factors of fecundability. Recent research on medically assisted conception is adding to the understanding of declining fecundity with age, especially the relative contributions of endometrial and ovarian ageing. This paper reviews the available information on declining fertility with age and discusses the implications of the extension of fertility through new medical technologie
False positives complicate ancient pathogen identifications using high-throughput shotgun sequencing
Background: Identification of historic pathogens is challenging since false positives and negatives are a serious risk. Environmental non-pathogenic contaminants are ubiquitous. Furthermore, public genetic databases contain limited information regarding these species. High-throughput sequencing may help reliably detect and identify historic pathogens. Results: We shotgun-sequenced 8 16th-century Mixtec individuals from the site of Teposcolula Yucundaa (Oaxaca, Mexico) who are reported to have died from the huey cocoliztli (‘Great Pestilence’ in Nahautl), an unknown disease that decimated native Mexican populations during the Spanish colonial period, in order to identify the pathogen. Comparison of these sequences with those deriving from the surrounding soil and from 4 precontact individuals from the site found a wide variety of contaminant organisms that confounded analyses. Without the comparative sequence data from the precontact individuals and soil, false positives for Yersinia pestis and rickettsiosis could have been reported. Conclusions: False positives and negatives remain problematic in ancient DNA analyses despite the application of high-throughput sequencing. Our results suggest that several studies claiming the discovery of ancient pathogens may need further verification. Additionally, true single molecule sequencing’s short read lengths, inability to sequence through DNA lesions, and limited ancient-DNA-specific technical development hinder its application to palaeopathology
Accretion disc formation around the neutron star in Be/X-ray binaries
We study the accretion on to the neutron star in Be/X-ray binaries, using a
3D SPH code and the data imported from a simulation by \citet{oka2} for a
coplanar system with a short period () and a moderate
eccentricity , which targeted the Be/X-ray binary 4U 0115+63. For
simplicity, we adopt the polytropic equation of state. We find that a
time-dependent accretion disc is formed around the neutron star regardless of
the simulation parameters. In the long term, the disc evolves via a two-stage
process, which consists of the initial developing stage and the later developed
stage. The developed disc is nearly Keplerian. In the short term, the disc
structure modulates with the orbital phase. The disc shrinks at the periastron
passage of the Be star and restores its radius afterwards. The accretion rate
on to the neutron star is also phase dependent, but its peak is broader and
much lower than that of the mass-transfer rate from the Be disc, unless the
polytropic exponent is as large as 5/3. Our simulations show that the truncated
Be disk model for Be/X-ray binaries is consistent with the observed X-ray
behaviour of 4U 0115+63.Comment: 13pages, 62figures, accepted to MNRAS. Revised version adds in 4 new
figures, in which we have improved the English, kindly pointed out by Manson
Katherine. For associated movies, see
http://astro3.sci.hokudai.ac.jp/~kimi/movie.htm
Discovery of periodicities in two highly variable intermediate polars towards the Galactic Center
We discovered Fe complex emission and pulsation in two highly
variable sources (4XMM J174917.7--283329, 4XMM J174954.6--294336). The
equivalent widths of 6.4 and 6.7 keV lines of 4XMM J174917.7--283329 are
and eV, respectively. The continuum is
fitted by a partially absorbed apec model with plasma temperature of
keV. The inferred mass of the white dwarf (WD) is
. We detected pulsations with a period of
s and a pulsed fraction of . The light curves of 4XMM
J174954.6--294336 display asymmetric eclipse and dipping behaviour. To date,
this is only the second intermediate polar (IP) that shows a total eclipse in
X-rays. The spectrum of the sources is characterized by a power-law model with
photon index . The equivalent widths of the 6.4 keV and 6.7
keV iron lines are and eV, respectively.
The continuum is described by emission from optically thin plasma with a
temperature of keV. The inferred mass of the WD is
. We discovered coherent pulsations from the
source with a period of s. The pulsed fraction is . The
measured spin period, hard photon index, and equivalent width of the
fluorescent Fe line in both sources are consistent with the values
found in IP. While 4XMM J174954.6--294336 was already previously classified as
an IP, we also suggest 4XMM J174917.7--283329 as a new IP. The X-ray eclipses
in 4XMM J174954.6--294336 are most likely caused by a low-mass companion star
obscuring the central X-ray source. The asymmetry in the eclipse is likely
caused by a thick bulge that intercepts the line of sight during the ingress
phase but not during the egress phase located behind the WD along the line of
sight.Comment: 9 pages, six figures, accepted for publication in A&
A Random Shuffle Method to Expand a Narrow Dataset and Overcome the Associated Challenges in a Clinical Study: A Heart Failure Cohort Example
Heart failure (HF) affects at least 26 million people worldwide, so predicting adverse events in HF patients represents a major target of clinical data science. However, achieving large sample sizes sometimes represents a challenge due to difficulties in patient recruiting and long follow-up times, increasing the problem of missing data. To overcome the issue of a narrow dataset cardinality (in a clinical dataset, the cardinality is the number of patients in that dataset), population-enhancing algorithms are therefore crucial. The aim of this study was to design a random shuffle method to enhance the cardinality of an HF dataset while it is statistically legitimate, without the need of specific hypotheses and regression models. The cardinality enhancement was validated against an established random repeated-measures method with regard to the correctness in predicting clinical conditions and endpoints. In particular, machine learning and regression models were employed to highlight the benefits of the enhanced datasets. The proposed random shuffle method was able to enhance the HF dataset cardinality (711 patients before dataset preprocessing) circa 10 times and circa 21 times when followed by a random repeated-measures approach. We believe that the random shuffle method could be used in the cardiovascular field and in other data science problems when missing data and the narrow dataset cardinality represent an issue
No Confirmed New Isolated Neutron Stars In The SDSS Data Release 4
We report on follow-up observations of candidate X-ray bright, radio-quiet
isolated neutron stars (INSs) identified from correlations of the ROSAT All-Sky
Survey (RASS) and the Sloan Digital Sky Survey (SDSS) Data Release 4 in
Ag\"ueros et al. (2006). We obtained Chandra X-ray Telescope exposures for 13
candidates in order to pinpoint the source of X-ray emission in optically blank
RASS error circles. These observations eliminated 12 targets as good INS
candidates. We discuss subsequent observations of the remaining candidate with
the XMM-Newton X-ray Observatory, the Gemini North Observatory, and the Apache
Point Observatory. We identify this object as a likely extragalactic source
with an unusually high log(fX/fopt) ~ 2.4. We also use an updated version of
the population synthesis models of Popov et al. (2010) to estimate the number
of RASS-detected INSs in the SDSS Data Release 7 footprint. We find that these
models predict ~3-4 INSs in the 11,000 square deg imaged by SDSS, which is
consistent with the number of known INSs that fall within the survey footprint.
In addition, our analysis of the four new INS candidates identified by Turner
et al. (2010) in the SDSS footprint implies that they are unlikely to be
confirmed as INSs; together, these results suggest that new INSs are not likely
to be found from further correlations of the RASS and SDSS.Comment: 11 pages, 2 figures, 3 tables; accepted for publication in A
Algebraic volume density property of affine algebraic manifolds
We introduce the notion of algebraic volume density property for affine
algebraic manifolds and prove some important basic facts about it, in
particular that it implies the volume density property. The main results of the
paper are producing two big classes of examples of Stein manifolds with volume
density property. One class consists of certain affine modifications of \C^n
equipped with a canonical volume form, the other is the class of all Linear
Algebraic Groups equipped with the left invariant volume form.Comment: 35 page
Non variability of intervening absorbers observed in the UVES spectra of the "naked-eye" GRB080319
The aim of this paper is to investigate the properties of the intervening
absorbers lying along the line of sight of Gamma-Ray Burst (GRB) 080319B
through the analysis of its optical absorption features. To this purpose, we
analyze a multi-epoch, high resolution spectroscopic observations (R=40000,
corresponding to 7.5 km/s) of the optical afterglow of GRB080319B (z=0.937),
taken with UVES at the VLT. Thanks to the rapid response mode (RRM), we
observed the afterglow just 8m:30s after the GRB onset when the magnitude was R
~ 12. This allowed us to obtain the best signal-to-noise, high resolution
spectrum of a GRB afterglow ever (S/N per resolution element ~ 50). Two further
RRM and target of opportunity observations were obtained starting 1.0 and 2.4
hours after the event, respectively. Four MgII absorption systems lying along
the line of sight to the afterglow have been detected in the redshift range 0.5
< z < 0.8, most of them showing a complex structure featuring several
components. Absorptions due to FeII, MgI and MnII are also present; they appear
in four, two and one intervening absorbers, respectively. One out of four
systems show a MgII2796 rest frame equivalent width larger than 1A. This
confirms the excess of strong MgII absorbers compared to quasars, with dn/dz =
0.9, ~ 4 times larger than the one observed along quasar lines of sight. In
addition, the analysis of multi-epoch, high-resolution spectra allowed us to
exclude a significant variability in the column density of the single
components of each absorber. Combining this result with estimates of the size
of the emitting region, we can reject the hypothesis that the difference
between GRB and QSO MgII absorbers is due to a different size of the emitting
regions.Comment: 10 pages, 15 ps figures, submitted to MNRA
Chandra Observation of the Globular Cluster NGC 6440 and the Nature of Cluster X-ray Luminosity Functions
As part of our campaign to determine the nature of the various source
populations of the low-luminosity globular cluster X-ray sources, we have
obtained a Chandra X-ray Observatory ACIS-S3 image of the globular cluster NGC
6440. We detect 24 sources to a limiting luminosity of ~2 times 10^31 erg/s
(0.5-2.5keV) inside the cluster's half-mass radius, all of which lie within ~2
core radii of the cluster center. We also find excess emission in and around
the core which could be due to unresolved point sources. Based upon X-ray
luminosities and colors, we conclude that there are 4-5 likely quiescent
low-mass X-ray binaries and that most of the other sources are cataclysmic
variables. We compare these results to Chandra results from other globular
clusters and find the X-ray luminosity functions differ among the clusters.Comment: 9 pages, 4 figures, accepted by ApJ, minor changes, added table of
clusters' physical parameter
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