Spectroscopy of high mass X-ray binaries with Swift/XRT

We present the X-ray spectroscopy study of three high mass X-ray binary systems, Vela X-1, Cen X-3 and V0332+53 using data obtained with Swift/XRT. The continuum emission of Vela X-1 is consistent with two absorbed power laws, each of them modified by different absorbing columns and with the same power law index. Moreover, the high energy part of the spectrum is modified by absorption components, like Gaussian profile, smedge} or edge} functions. We also detect emission lines and fit as Gaussians at 6.406^+0.004_-0.021 keV (Fe Kalpha) and 2.44^+0.04_-0.03 keV (S XV He_alpha). The continuum emission of Cen X-3 is consistent with two absorbed power laws, each of them modified by different absorbing columns and with the same power law index. We also detect emission lines and fit as Gaussians at 6.432^+0.020_-0.023 keV (Fe Kalpha), 6.84^+0.12_-0.10 keV (Fe XXVI), 2.90 +/- 0.18 keV Ar Kalpha and 1.12^+0.07_-0.06 keV (Ne X Ly_alpha). The presence of iron emission lines at 6.4 keV and 6.8 keV simultaneously indicates that there are at least two distinct emission sites. Fluorescence in a localized region of relatively low ionization may be responsible for the 6.4 keV emission. We could interpret the emission line at 6.8 keV as a blend of several narrow lines due to scattering of radiation from the neutron star in an extended highly ionized stellar wind. Finally, the continuum emission of V0332+53 is consistent with an absorbed power law and a Gaussian emission line to describe the soft excess at low energies. No emission lines are present in this system.Part of this work was supported by the Spanish Ministry of Education and Science Primera ciencia con el GTC: La astronomía española en vanguardia de la astronomía europea CSD200670 and Multiplicidad y evolución de estrellas masivas project number AYA200806166C0303. KLP and JPO acknowledge support from STFC. JMT & JJRR acknowledge support by the Spanish Ministerio de Educación y Ciencia (MEC) under grants PR2007-0176 & PR2009-0455. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester

Resolving iron emission lines in 4U 1538-52 with XMM-Newton

The X-ray Universe 2011, Presentations of the Conference held in Berlin, Germany, 27-30 June 2011. Available online at: http://xmm.esac.esa.int/external/xmm_science/workshops/2011symposium/, article id.275We present the results of a XMM-Newton observation of the high-mass X-ray binary 4U 1538-52 at orbital phases between 0.75-1.00 (in the eclipse-ingress phase). Here we concentrate on the study of discrete features in the energy range from 5.9 keV to 7.8 keV, i.e. on the iron Kα line region, using the EPIC/PN instrument on board XMM-Newton observatory. We clearly see a Kα neutral iron line at around 6.4 keV and were able to distinguish two hot lines from highly photoionized Fe XXV and Fe XXVI. We discuss the implications of the simultaneous presence of iron with both low and high ionization levels.This work was supported by the Spanish Ministry of Education and Science De INTEGRAL a IXO: binarias de rayos X y estrellas activas AYA2010-15431 and partially supported by Primera ciencia con el GTC: La astronomía española en vanguardia de la astronomía europea CSD200670. KLP and JPO acknowledge support from the UK Space Agency. JJRR acknowledges support by the Spanish Ministerio de Educación y Ciencia (MEC) under grant PR2009-0455. This work made use of data obtained through the XMM-Newton Science Archive (XSA), rovided by European Space Agency (ESA)

Trapping in the random conductance model

We consider random walks on $\Z^d$ among nearest-neighbor random conductances which are i.i.d., positive, bounded uniformly from above but whose support extends all the way to zero. Our focus is on the detailed properties of the paths of the random walk conditioned to return back to the starting point at time $2n$. We show that in the situations when the heat kernel exhibits subdiffusive decay --- which is known to occur in dimensions $d\ge4$ --- the walk gets trapped for a time of order $n$ in a small spatial region. This shows that the strategy used earlier to infer subdiffusive lower bounds on the heat kernel in specific examples is in fact dominant. In addition, we settle a conjecture concerning the worst possible subdiffusive decay in four dimensions.Comment: 21 pages, version to appear in J. Statist. Phy

Transcatheter Aortic Valve Implantation in Dialysis Patients

Background/Aims: Transcatheter aortic valve implantation (TAVI) has emerged as a new therapeutic option for high-risk patients. However, dialysis patients were excluded from all previous studies. The aim of this study is to compare the outcomes of TAVI for dialysis patients with those for patients with chronic kidney disease (CKD) stages 3 and 4 and to compare TAVI with open surgery in dialysis patients. Methods: Part I: comparison of 10 patients on chronic hemodialysis with 116 patients with non-dialysis-dependent CKD undergoing TAVI. Part II: comparison of transcatheter (n = 15) with open surgical (n = 24) aortic valve replacement in dialysis patients. Results: Part I: dialysis patients were significantly younger (72.3 vs. 82.0 years; p < 0.01). Hospital stay was significantly longer in dialysis patients (21.8 vs. 12.1 days; p = 0.01). Overall 30-day mortality was 3.17%, with no deaths among dialysis patients. Six-month survival rates were similar (log-rank p = 0.935). Part II: patient age was comparable (66.5 vs. 69.5 years; p = 0.42). Patients in the surgical group tended to stay longer in hospital than TAVI patients (29.5 vs. 22.5 days; p = 0.35). Conclusion: TAVI is a safe procedure in patients on chronic hemodialysis. Until new data become available, we find no compelling reason to refuse these patients TAVI. Copyright (C) 2012 S. Karger AG, Base

Be‐10 dating of ice‐marginal moraines in the Khumbu Valley, Nepal, Central Himalaya, reveals the response of monsoon‐influenced glaciers to Holocene climate change

The dynamic response of large mountain glaciers to climatic forcing operates over timescales of several centuries and therefore understanding how these glaciers change requires observations of their behavior through the Holocene. We used Be-10 exposure-age dating and geomorphological mapping to constrain the evolution of glaciers in the Khumbu Valley in the Everest region of Nepal. Khumbu and Lobuche Glaciers are surrounded by high-relief lateral and terminal moraines from which seven glacial stages were identified and dated to 7.4 ± 0.2, 5.0 ± 0.3, 3.9 ± 0.1, 2.8 ± 0.2, 1.3 ± 0.1, 0.9 ± 0.02, and 0.6 ± 0.16 ka. These stages correlate to each of the seven latest Holocene regional glacial stages identified across the monsoon-influenced Himalaya, demonstrating that a coherent record of high elevation terrestrial palaeoclimate change can be extracted from dynamic mountain landscapes. The time-constrained moraine complex represents a catchment-wide denudation rate of 0.8–1.4 mm a−1 over the last 8 kyr. The geometry of the ablation area of Khumbu Glacier changed around 4 ka from a broad, shallow ice tongue to become narrower and thicker as restricted by the topographic barrier of the terminal moraine complex

Discovery of a QPO in the X-ray pulsar 1A 1118-615: correlated spectral and aperiodic variability

Our goal is to investigate the X-ray timing and spectral variability of the high-mass X-ray binary 1A 1118-615 during a type-II outburst. We performed a detailed color, spectral and timing analysis of a giant outburst from 1A 1118-615, using RXTE data. Results. We report the discovery of a variable quasi-periodic oscillation (QPO) in the power spectral density of 1A 1118-615, with a centroid frequency of ~0.08 Hz. The centroid frequency of the QPO correlates with the X-ray flux, as expected according to the most accredited models for QPO production. For energies above ~4 keV, the QPO rms variability decreases as the energy increases. Pulse profiles display energy dependence, with a two-peak profile at lower energies, and a single peak at higher energies. From spectral analysis, we confirm the presence of a cyclotron absorption feature at ~60 keV, the highest value measured for an X-ray pulsar. We find that the spectral parameters (photon index, cutoff energy, iron fluorescence line strength) display a marked dependence with flux. We detect two different levels of neutral hydrogen column density, possibly due to the Be companion activity. We report for the first time a correlation between the timing and spectral parameters in an X-ray pulsar. All the correlations found between spectral/timing parameters and X-ray flux are present up to a flux of ~6x10^-9 erg cm^-2 s^-1, when a saturation level is reached. We propose that the saturation observed corresponds to the minimum extent of the neutron star magnetosphere. We estimate the magnetic field of the neutron star from two independent ways, using results from spectral (cyclotron line energy) and timing (QPO frequency) analysis, obtaining consistent values, of ~7-8x10^12 G. Results from the comprehensive spectral and timing analysis are discussed in comparison with other X-ray pulsars.Comment: 9 pages, 11 figures. Accepted for publication in Astronomy and Astrophysic

Perturbation expansion for 2-D Hubbard model

We develop an efficient method to calculate the third-order corrections to the self-energy of the hole-doped two-dimensional Hubbard model in space-time representation. Using the Dyson equation we evaluate the renormalized spectral function in various parts of the Brillouin zone and find significant modifications with respect to the second-order theory even for rather small values of the coupling constant U. The spectral function becomes unphysical for $U \simeq W$, where W is the half-width of the conduction band. Close to the Fermi surface and for U<W, the single-particle spectral weight is reduced in a finite energy interval around the Fermi energy. The increase of U opens a gap between the occupied and unoccupied parts of the spectral function.Comment: 17 pages, 11 Postscript figures, Phys. Rev. B, accepte

Acute kidney injury following transcatheter aortic valve implantation: predictive factors, prognostic value, and comparison with surgical aortic valve replacement

Aims: Very few data exist on the occurrence of acute kidney injury (AKI) associated with transcatheter aortic valve implantation (TAVI). The objectives of the present study were (i) to determine the incidence, predictive factors, and prognostic value of AKI following TAVI, and (ii) to compare the occurrence of AKI in TAVI vs. surgical aortic valve replacement (SAVR) in patients with pre-procedural chronic kidney disease (CKD). Methods and results: A total of 213 patients (mean age 82 ± 8 years) undergoing TAVI for the treatment of severe aortic stenosis were included in the study. Acute kidney injury was defined as a reduction of >25% in estimated glomerular filtration rate (eGFR) within 48 h following the procedure or the need for haemodialysis during index hospitalization. Those patients with pre-procedural CKD (eGFR <60 mL/min/1.73 m2, n = 119) were compared with 104 contemporary patients with CKD who underwent isolated SAVR. The incidence of AKI following TAVI was 11.7%, with 1.4% of the patients requiring haemodialysis. Predictive factors of AKI were hypertension (OR: 4.66; 95% CI: 1.04–20.87), chronic obstructive pulmonary disease (OR: 2.64, 95% CI: 1.10–6.36), and peri-operative blood transfusion (OR: 3.47, 95% CI: 1.30–9.29). Twenty-one patients (9.8%) died during index hospitalization, and the logistic EuroSCORE (OR: 1.03 for each increase of 1%; 95% CI: 1.01–1.06) and occurrence of AKI (OR: 4.14, 95% CI: 1.42–12.13) were identified as independent predictors of postoperative mortality. Patients with CKD who underwent TAVI were older, had a higher logistic EuroSCORE and lower pre-procedural eGFR values compared with those who underwent SAVR (P < 0.0001 for all). The incidence of AKI was lower (P = 0.001; P = 0.014 after propensity score adjustment) in CKD patients who underwent TAVI (9.2%, need for haemodialysis: 2.5%) compared with those who underwent SAVR (25.9%, need for haemodialysis: 8.7%). Conclusion: Acute kidney injury occurred in 11.7% of the patients following TAVI and was associated with a greater than four-fold increase in the risk of postoperative mortality. Hypertension, chronic obstructive pulmonary disease, and blood transfusion were predictive factors of AKI. In those patients with pre-procedural CKD, TAVI was associated with a significant reduction of AKI compared with SAVR

Detecting emission lines with XMM-Newton in 4U 1538–52

Context. The properties of the X-ray emission lines are a fundamental tool for studying the nature of the matter surrounding the neutron star and the phenomena that produce these lines. Aims. The aim of this work is to analyse the X-ray spectrum of 4U 1538−52 obtained by the XMM-Newton observatory and to look for the presence of diagnostic lines in the energy range 0.3−11.5 keV. Methods. We used a 54 ks PN & MOS/XMM-Newton observation of the high-mass X-ray binary 4U 1538−52 covering the orbital phase between 0.75 to 1.00 (the eclipse ingress). We modelled the 0.3−11.5 keV continuum emission with three absorbed power laws and looked for the emission lines. Results. We found previously unreported recombination lines in this system at ~2.4 keV, ~1.9 keV, and ~1.3 keV, which is consistent with the presence of highly ionized states of S XV Heα, Si XIII Heα, and either Mg Kα or Mg XI Heα. On the other hand, in spectra that are both out of eclipse and in eclipse, we detect a fluorescence iron emission line at 6.4 keV, which is resolved into two components: a narrow (σ ≤ 10 eV) fluorescence Fe Kα line plus one hot line from highly photoionized Fe XXV. Conclusions. The detection of new recombination lines during eclipse ingress in 4U 1538−52 indicates that there is an extended ionized region surrounding the neutron star.Part of this work was supported by the Spanish Ministry of Education and Science Primera ciencia con el GTC: La astronomía española en vanguardia de la astronomía europea CSD200670 and Multiplicidad y evolución de estrellas masivas project number AYA200806166C0303 and partially supported by AYA2010-15431. J.J.R.R. acknowledges the support by the Spanish Ministerio de Educación y Ciencia under grant PR2009-0455