Matching of spatially homogeneous non-stationary space--times to vacuum in cylindrical symmetry

We study the matching of LRS spatially homogeneous collapsing dust space-times with non-stationary vacuum exteriors in cylindrical symmetry. Given an interior with diagonal metric we prove existence and uniqueness results for the exterior. The matched solutions contain trapped surfaces, singularities and Cauchy horizons. The solutions cannot be asymptotically flat and we present evidence that they are singular on the Cauchy horizons.Comment: LaTeX, 15 pages, 1 figure, submitted for publicatio

On the evolution of the inner disk radius with flux in the neutron star low-mass X-ray binary Serpens X-1

We analyze the latest \emph{Suzaku} observation of the bright neutron star low-mass X-ray binary Serpens X-1 taken in 2013 October and 2014 April. The observation was taken using the burst mode and only suffered mild pile-up effects. A broad iron line is clearly detected in the X-ray spectrum. We test different models and find that the iron line is asymmetric and best interpreted by relativistic reflection. The relativistically broadened iron line is generally believed to originate from the innermost regions of the accretion disk, where strong gravity causes a series of special and general relativistic effects. The iron line profile indicates an inner radius of $\sim8$ $R_{\rm G}$, which gives an upper limit on the size of the neutron star. The asymmetric iron line has been observed in a number of previous observations, which gives several inner radius measurements at different flux states. We find that the inner radius of Serpens X-1 does not evolve significantly over the range of $L/L_{\rm Edd}\sim0.4-0.6$, and the lack of flux dependence of the inner radius implies that the accretion disk may be truncated outside the innermost stable circular orbit by the boundary layer rather than the stellar magnetic field.Comment: 8 pages, 6 figures, accepted for publication in Ap

Discovery of a 6.4 keV Emission Line in a Burst from SGR 1900+14

We present evidence of a 6.4 keV emission line during a burst from the soft gamma-ray repeater SGR 1900+14. The Rossi X-ray Timing Explorer (RXTE) monitored this source extensively during its outburst in the summer of 1998. A strong burst observed on August 29, 1998 revealed a number of unique properties. The burst exhibits a precursor and is followed by a long (~ 1000 s) tail modulated at the 5.16 s stellar rotation period. The precursor has a duration of 0.85 s and shows both significant spectral evolution as well as an emission feature centered near 6.4 keV during the first 0.3 s of the event, when the X-ray spectrum was hardest. The continuum during the burst is well fit with an optically thin thermal bremsstrahlung (OTTB) spectrum with the temperature ranging from about 40 to 10 keV. The line is strong, with an equivalent width of 400 eV, and is consistent with Fe K-alpha fluorescence from relatively cool material. If the rest-frame energy is indeed 6.4 keV, then the lack of an observed redshift indicates that the source is at least 80 km above the neutron star surface. We discuss the implications of the line detection in the context of models for SGRs.Comment: AASTex preprint, 14 pages, 3 embedded figures. Accepted for Publication in Astrophysical Journal Letter

On the central quadric ansatz: integrable models and Painleve reductions

It was observed by Tod and later by Dunajski and Tod that the Boyer-Finley (BF) and the dispersionless Kadomtsev-Petviashvili (dKP) equations possess solutions whose level surfaces are central quadrics in the space of independent variables (the so-called central quadric ansatz). It was demonstrated that generic solutions of this type are described by Painleve equations PIII and PII, respectively. The aim of our paper is threefold: -- Based on the method of hydrodynamic reductions, we classify integrable models possessing the central quadric ansatz. This leads to the five canonical forms (including BF and dKP). -- Applying the central quadric ansatz to each of the five canonical forms, we obtain all Painleve equations PI - PVI, with PVI corresponding to the generic case of our classification. -- We argue that solutions coming from the central quadric ansatz constitute a subclass of two-phase solutions provided by the method of hydrodynamic reductions.Comment: 12 page

A Fast X-ray Disk Wind in the Transient Pulsar IGR J17480-2446 in Terzan 5

Accretion disk winds are revealed in Chandra gratings spectra of black holes. The winds are hot and highly ionized (typically composed of He-like and H-like charge states) and show modest blueshifts. Similar line spectra are sometimes seen in dipping low-mass X-ray binaries (LMXBs), which are likely viewed edge-on; however, that absorption is tied to structures in the outer disk, and blueshifts are not typically observed. Here, we report the detection of blueshifted He-like Fe XXV (3100 ± 400 km s-1) and H-like Fe XXVI (1000 ± 200 km s-1) absorption lines in a Chandra/HETG spectrum of the transient pulsar and LMXB IGR J17480-2446 in Terzan 5. These features indicate a disk wind with at least superficial similarities to those observed in stellar-mass black holes. The wind does not vary strongly with numerous weak X-ray bursts or flares. A broad Fe K emission line is detected in the spectrum, and fits with different line models suggest that the inner accretion disk in this system may be truncated. If the stellar magnetic field truncates the disk, a field strength of B= (0.7-4.0)×109 G is implied, which is in line with estimates based on X-ray timing techniques. We discuss our findings in the context of accretion flows onto neutron stars and stellar-mass black holes

On quasi-local charges and Newman--Penrose type quantities in Yang--Mills theories

We generalize the notion of quasi-local charges, introduced by P. Tod for Yang--Mills fields with unitary groups, to non-Abelian gauge theories with arbitrary gauge group, and calculate its small sphere and large sphere limits both at spatial and null infinity. We show that for semisimple gauge groups no reasonable definition yield conserved total charges and Newman--Penrose (NP) type quantities at null infinity in generic, radiative configurations. The conditions of their conservation, both in terms of the field configurations and the structure of the gauge group, are clarified. We also calculate the NP quantities for stationary, asymptotic solutions of the field equations with vanishing magnetic charges, and illustrate these by explicit solutions with various gauge groups.Comment: 22 pages, typos corrected, appearing in Classical and Quantum Gravit

RXTE Observations of 1A 1744-361: Correlated Spectral and Timing Behavior

We analyze Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of the transient low mass X-ray binary (LMXB) system 1A 1744-361. We explore the X-ray intensity and spectral evolution of the source, perform timing analysis, and find that 1A 1744-361 shows `atoll' behavior during the outbursts. The color-color diagram indicates that this LMXB was observed in a low intensity spectrally hard (low-hard) state and in a high intensity `banana' state. The low-hard state shows a horizontal pattern in the color-color diagram, and the previously reported `dipper QPO' appears only during this state. We also perform energy spectral analyses, and report the first detection of broad iron emission line and iron absorption edge from 1A 1744-361.Comment: 20 pages, 4 tables, 4 figures, accepted for publication in Ap

Compact Einstein-Weyl four-dimensional manifolds

We look for four dimensional Einstein-Weyl spaces equipped with a regular Bianchi metric. Using the explicit 4-parameters expression of the distance obtained in a previous work for non-conformally-Einstein Einstein-Weyl structures, we show that only four 1-parameter families of regular metrics exist on orientable manifolds : they are all of Bianchi $IX$ type and conformally K\"ahler ; moreover, in agreement with general results, they have a positive definite conformal scalar curvature. In a Gauduchon's gauge, they are compact and we obtain their topological invariants. Finally, we compare our results to the general analyses of Madsen, Pedersen, Poon and Swann : our simpler parametrisation allows us to correct some of their assertions.Comment: Latex file, 13 pages, an important reference added and a critical discussion of its claims offered, others minor modification

The association between care left undone and temporary Nursing staff ratios in acute settings: a cross- sectional survey of registered nurses

Background The shortage of health workers is a global phenomenon. To meet increasing patient demands on UK health services, providers are increasingly relying on temporary staff to fill permanent posts. This study examines the occurrence of ‘care left undone’, understaffing and temporary staffing across acute sector settings. Methods “Secondary data analysis from an RCN administered online survey covering nurses from hospitals and trusts across all four UK countries. Staffing and ‘care left undone’ measures were derived from the responses of 8841 registered nurses across the UK. A locally smoothed scatterplot smoothing regression analysis (Loess) was used to model the relationship between any ‘care left undone’ events and full complement, modest and severely understaffed shifts, and proportions of temporary staff. Results Occurrence of ‘care left undone’ was highest in Emergency Departments (48.4%) and lowest in Theatre settings (21%). The odds of ‘care left undone’ increase with increasing proportion of temporary staff. This trend is the same in all understaffing categories. On shifts with a full quota of nursing staff, an increase in the proportion of temporary staff from 0 to 10% increases the odds of care left undone by 6% (OR = 1.06, 95% CI, 1.04–1.09). Within the full quota staffing category, the difference becomes statistically significant (p < 0.05) on shifts with a proportion of temporary nursing staff of 40% or more. On shifts with a full quota of nursing staff the odds of a ‘care left undone’ event is 10% more with the proportion of temporary nursing staff at 50%, compared to shifts with modest understaffing of 25% or less with no temporary nursing staff (OR = 1.1, 95%CI, 0.96–1.25). Conclusion The odds of a ‘care left undone’ event are similar for fully staffed shifts with a high temporary nursing staff ratio compared to severely understaffed shifts with no temporary nursing staff. Increasing the proportion of temporary nurse staff is associated with higher rates of self-reported care left undone by nursing staff. This has significant implications for nurse managers and policy makers