57 research outputs found
Understanding the LMXB X2127+119 in M15 I. X-ray eclipses and dips
We present X-ray observations of the high-inclination low-mass X-ray binary
system X2127+119 (AC211) in the globular cluster M15 (NGC 7078). The
observations consist of data acquired in 1996 with the RXTE satellite and in
1995 with the ASCA satellite. Also, the MPC1 data from the 1988 GINGA
observations were de-archived and re-analysed. The phase-folded 2-10 keV
hardness ratios from all three missions differ significantly indicating that
the system can exhibit different spectral behaviours. We find that the X-ray
eclipse profiles can be described relatively well using a simple model where
the secondary star passes in front of a large X-ray emitting region. For this
we require a mass ratio (q=M1/M2) of about one. The radius of this X-ray
emitting region is ~0.8 RL1 and its vertical extent 60 degrees above the
orbital plane. We suggest that if this X-ray emitting region were an optically
thick corona, it would explain various puzzling aspects of this system. We also
show that the X-ray dip observed at phases around 0.65 does not conform with
the idea that the dip is caused by vertically extended material associated with
the stream/disc impact region, but that it could be due to structure in the
inner parts of the disc.Comment: 12 pages, 14 figures, accepted for publication in A&
Discovery of X-ray absorption features from the dipping low-mass X-ray binary XB 1916-053 with XMM-Newton
We report the discovery of narrow Fe XXV and Fe XXVI K alpha X-ray absorption
lines at 6.65 and 6.95 keV in the persistent emission of the dipping low-mass
X-ray binary (LMXB) XB 1916-053 during an XMM-Newton observation performed in
September 2002. In addition, there is marginal evidence for absorption features
at 1.48 keV, 2.67 kev, 7.82 keV and 8.29 keV consistent with Mg XII, S XVI, Ni
XXVII K alpha and Fe XXVI K beta transitions, respectively. Such absorption
lines from highly ionized ions are now observed in a number of high inclination
(ie. close to edge-on) LMXBs, such as XB 1916-053, where the inclination is
estimated to be between 60-80 degrees. This, together with the lack of any
orbital phase dependence of the features (except during dips), suggests that
the highly ionized plasma responsible for the absorption lines is located in a
cylindrical geometry around the compact object. Using the ratio of Fe XXV and
Fe XXVI column densities, we estimate the photo-ionization parameter of the
absorbing material to be 10^{3.92} erg cm s^{-1}. Only the Fe XXV line is
observed during dipping intervals and the upper-limits to the Fe XXVI column
density are consistent with a decrease in the amount of ionization during
dipping intervals. This implies the presence of cooler material in the line of
sight during dipping. We also report the discovery of a 0.98 keV absorption
edge in the persistent emission spectrum. The edge energy decreases to 0.87 keV
during deep dipping intervals. The detected feature may result from edges of
moderately ionized Ne and/or Fe with the average ionization level decreasing
from persistent emission to deep dipping. This is again consistent with the
presence of cooler material in the line of sight during dipping.Comment: 13 pages, accepted for publication in Astronomy and Astrophysic
Formation of millisecond pulsars with CO white dwarf companions - II. Accretion, spin-up, true ages and comparison to MSPs with He white dwarf companions
Millisecond pulsars (MSPs) are mainly characterised by their spin periods,
B-fields and masses - quantities which are largely affected by previous
interactions with a companion star in a binary system. In this paper, we
investigate the formation mechanism of MSPs by considering the pulsar recycling
process in both intermediate-mass X-ray binaries (IMXBs) and low-mass X-ray
binaries (LMXBs). The IMXBs mainly lead to the formation of binary MSPs with a
massive carbon-oxygen (CO) or an oxygen-neon-magnesium white dwarf (ONeMg WD)
companion, whereas the LMXBs form recycled pulsars with a helium white dwarf
(He WD) companion. We discuss the accretion physics leading to the spin-up line
in the PPdot-diagram and demonstrate that such a line cannot be uniquely
defined. We derive a simple expression for the amount of accreted mass needed
for any given pulsar to achieve its equilibrium spin and apply this to explain
the observed differences of the spin distributions of recycled pulsars with
different types of companions. From numerical calculations we present further
evidence for significant loss of rotational energy in accreting X-ray MSPs in
LMXBs during the Roche-lobe decoupling phase (Tauris 2012) and demonstrate that
the same effect is negligible in IMXBs. We examine the recycling of pulsars
with CO WD companions via Case BB Roche-lobe overflow (RLO) of naked helium
stars in post common envelope binaries. We find that such pulsars typically
accrete of the order 0.002-0.007 M_sun which is just about sufficient to
explain their observed spin periods. We introduce isochrones of radio MSPs in
the PPdot-diagram to follow their spin evolution and discuss their true ages
from comparison with observations. Finally, we apply our results of the spin-up
process to the massive pulsar J1614-2230 (Paper I) and put new constraints on
the birth masses of a number of recycled pulsars. [Abridged]Comment: MNRAS in press, 32 pages, 14 figures, 4 tables, appendix. Version 2:
minor typos correcte
Global optical/infrared - X-ray correlations in X-ray binaries: quantifying disc and jet contributions
The optical/near-infrared (OIR) region of the spectra of low-mass X-ray
binaries appears to lie at the intersection of a variety of different emission
processes. In this paper we present quasi-simultaneous OIR - X-ray observations
of 33 XBs in an attempt to estimate the contributions of various emission
processes in these sources, as a function of X-ray state and luminosity. A
global correlation is found between OIR and X-ray luminosity for low-mass black
hole candidate XBs (BHXBs) in the hard X-ray state, of the form L_OIR is
proportional to Lx^0.6. This correlation holds over 8 orders of magnitude in Lx
and includes data from BHXBs in quiescence and at large distances (LMC and
M31). A similar correlation is found in low-mass neutron star XBs (NSXBs) in
the hard state. For BHXBs in the soft state, all the near-infrared (NIR) and
some of the optical emission is suppressed below the correlation, a behaviour
indicative of the jet switching off/on in transition to/from the soft state. We
compare these relations to theoretical models of a number of emission
processes. We find that X-ray reprocessing in the disc and emission from the
jets both predict a slope close to 0.6 for BHXBs, and both contribute to the
OIR in BHXBs in the hard state, the jets producing ~90 percent of the NIR
emission at high luminosities. X-ray reprocessing dominates the OIR in NSXBs in
the hard state, with possible contributions from the jets (only at high
luminosity) and the viscously heated disc. We also show that the optically
thick jet spectrum of BHXBs extends to near the K-band. (abridged)Comment: Accepted for publication in MNRAS; 19 pages, 7 figure
Using Dynamic Stochastic Modelling to Estimate Population Risk Factors in Infectious Disease: The Example of FIV in 15 Cat Populations
BACKGROUND:In natural cat populations, Feline Immunodeficiency Virus (FIV) is transmitted through bites between individuals. Factors such as the density of cats within the population or the sex-ratio can have potentially strong effects on the frequency of fight between individuals and hence appear as important population risk factors for FIV. METHODOLOGY/PRINCIPAL FINDINGS:To study such population risk factors, we present data on FIV prevalence in 15 cat populations in northeastern France. We investigate five key social factors of cat populations; the density of cats, the sex-ratio, the number of males and the mean age of males and females within the population. We overcome the problem of dependence in the infective status data using sexually-structured dynamic stochastic models. Only the age of males and females had an effect (p = 0.043 and p = 0.02, respectively) on the male-to-female transmission rate. Due to multiple tests, it is even likely that these effects are, in reality, not significant. Finally we show that, in our study area, the data can be explained by a very simple model that does not invoke any risk factor. CONCLUSION:Our conclusion is that, in host-parasite systems in general, fluctuations due to stochasticity in the transmission process are naturally very large and may alone explain a larger part of the variability in observed disease prevalence between populations than previously expected. Finally, we determined confidence intervals for the simple model parameters that can be used to further aid in management of the disease
Perceived organizational membership and the retention of older workers
Drawing on the perceived organizational membership theoretical framework and the group-value justice model, we developed and tested a model predicting older workers\u27 intention to remain with their organization. We hypothesized that human resource practices targeted to older workers would be related to perceived insider status through how older workers perceived their supervisor managed these practices (perceived procedural and interpersonal justice). We also hypothesized that perceived insider status would mediate the relationship between perceived contribution and intention to remain. We conducted two studies to test the hypothesized model. Study 1 participants (N = 236) were a diverse group of older workers and Study 2 participants (N = 420) were older registered nurses. Using structural equation modeling, we found support for the hypothesized model. All of the hypothesized relationships were significant in Study 2 and all except one were significant in Study 1. Older workers will want to remain a member of their organization when their organization engages in practices tailored to the needs of older workers, their supervisor implements these practices fairly, and their organization conveys that it values the contribution of its older workers thereby fostering a strong sense of belonging
The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase
The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray
spectrometer, studied since 2015 for flying in the mid-30s on the Athena space
X-ray Observatory, a versatile observatory designed to address the Hot and
Energetic Universe science theme, selected in November 2013 by the Survey
Science Committee. Based on a large format array of Transition Edge Sensors
(TES), it aims to provide spatially resolved X-ray spectroscopy, with a
spectral resolution of 2.5 eV (up to 7 keV) over an hexagonal field of view of
5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement
Review (SRR) in June 2022, at about the same time when ESA called for an
overall X-IFU redesign (including the X-IFU cryostat and the cooling chain),
due to an unanticipated cost overrun of Athena. In this paper, after
illustrating the breakthrough capabilities of the X-IFU, we describe the
instrument as presented at its SRR, browsing through all the subsystems and
associated requirements. We then show the instrument budgets, with a particular
emphasis on the anticipated budgets of some of its key performance parameters.
Finally we briefly discuss on the ongoing key technology demonstration
activities, the calibration and the activities foreseen in the X-IFU Instrument
Science Center, and touch on communication and outreach activities, the
consortium organisation, and finally on the life cycle assessment of X-IFU
aiming at minimising the environmental footprint, associated with the
development of the instrument. Thanks to the studies conducted so far on X-IFU,
it is expected that along the design-to-cost exercise requested by ESA, the
X-IFU will maintain flagship capabilities in spatially resolved high resolution
X-ray spectroscopy, enabling most of the original X-IFU related scientific
objectives of the Athena mission to be retained. (abridged).Comment: 48 pages, 29 figures, Accepted for publication in Experimental
Astronomy with minor editin
The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase
The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory. Athena is a versatile observatory designed to address the Hot and Energetic Universe science theme, as selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), X-IFU aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over a hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR (i.e. in the course of its preliminary definition phase, so-called B1), browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters, such as the instrument efficiency, spectral resolution, energy scale knowledge, count rate capability, non X-ray background and target of opportunity efficiency. Finally, we briefly discuss the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, touch on communication and outreach activities, the consortium organisation and the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. Thanks to the studies conducted so far on X-IFU, it is expected that along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained. The X-IFU will be provided by an international consortium led by France, The Netherlands and Italy, with ESA member state contributions from Belgium, Czech Republic, Finland, Germany, Poland, Spain, Switzerland, with additional contributions from the United States and Japan.The French contribution to X-IFU is funded by CNES, CNRS and CEA. This work has been also supported by ASI (Italian Space Agency) through the Contract 2019-27-HH.0, and by the ESA (European Space Agency) Core Technology Program (CTP) Contract No. 4000114932/15/NL/BW and the AREMBES - ESA CTP No.4000116655/16/NL/BW. This publication is part of grant RTI2018-096686-B-C21 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”. This publication is part of grant RTI2018-096686-B-C21 and PID2020-115325GB-C31 funded by MCIN/AEI/10.13039/501100011033
Identification of Genomic Regions Associated with Phenotypic Variation between Dog Breeds using Selection Mapping
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Integrated analysis of the local and systemic changes preceding the development of post-partum cytological endometritis
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