Directional spectra comparisons between HF radar and a wave model

Directional spectra measurements using HF radar are compared with model data to confirm limitations of the currently available theory that underpins these measurements. In high seas, waveheight is overestimated but it is demonstrated that there is no clear impact on the shape of the spectrum which is in reasonable agreement with the model. The need for increased averaging before inversion is discussed

Identification of the X-ray pulsar in Hercules: A new optical pulsar

A series of photographic, photoelectric, and spectroscopic observations beginning June 1, 1972 has led to the optical identification of Her X-1 (2U 1705 + 34), a pulsed X-ray source in an eclipsing binary system, with the thirteenth magnitude blue variable star HZ Herculis. The detection of optical pulses at the frequency of the X-ray pulsar on three nights makes the identification conclusive and establishes HZ Her as the second known optical pulsar. The strength of the optical pulses may be correlated with the orbital phase but is not obviously related to the high or low intensity states of the X-ray source

Suitability of the Southern Australia Integrated Marine Observing System’s (SA-IMOS) HF-Radar for operational forecasting

The IMOS HF-Radar array in South Australia provides observations of the ocean waters south of Spencer Gulf. In addition to ocean surface currents, the data from this array can be processed to provide near-real time observations of wave statistics and wind direction. The Australian Bureau of Meteorology requires access to these observations for forecast modelling but currently only have a single Waverider buoy operating in South Australian waters at Cape du Couedic, south of Kangaroo Island, which provides no directional information. The HF-Radar array could potentially be used to augment the current operational observation systems used by the Bureau. In this paper we evaluate the performance of the HF-Radar system against observations from the Waverider buoy and an automatic weather station at Neptune Island and also compare the HF-Radar observations to a wave model based on the eSA-Marine forecast grid. The results suggest that upgrading the HF-Radar to provide near-real time wave and wind data would provide a new, independent source of environmental observations for the Bureau

HST/WFPC2 observations of the LMC pulsar PSR B0540-69

The study of the younger, and brighter, pulsars is important to understand the optical emission properties of isolated neutron stars. PSRB0540-69, the second brightest (V~22) optical pulsar, is obviously a very interesting target for these investigations. The aim of this work is threefold: constraining the pulsar proper motion and its velocity on the plane of the sky through optical astrometry, obtaining a more precise characterisation of the pulsar optical spectral energy distribution (SED) through a consistent set of multi-band, high-resolution, imaging photometry observations, measuring the pulsar optical phase-averaged linear polarisation, for which only a preliminary and uncertain measurement was obtained so far from ground-based observations. We performed high-resolution observations of PSRB0540-69 with the WFPC2 aboard the HST, in both direct imaging and polarimetry modes. From multi-epoch astrometry we set a 3sigma upper limit of 1 mas/yr on the pulsar proper motion, implying a transverse velocity <250 km/s at the 50 kpc LMC distance. Moreover, we determined the pulsar absolute position with an unprecedented accuracy of 70 mas. From multi-band photometry we characterised the pulsar power-law spectrum and we derived the most accurate measurement of the spectral index (0.70+/-0.07) which indicates a spectral turnover between the optical and X-ray bands. Finally, from polarimetry we obtained a new measurement of the pulsar phase-averaged polarisation degree (16+/-4%),consistent with magnetosphere models depending on the actual intrinsic polarisation degree and depolarisation factor, and we found that the polarisation vector (22+/-12deg position angle) is possibly aligned with the semi-major axis of the pulsar-wind nebula and with the apparent proper motion direction of its bright emission knot.Comment: 14 pages, 12 figures, accepted for publication in Astronomy & Astrophysic

BeppoSAX observations of the X-ray binary pulsar 4U1626-67

We report on observations of the low-mass X-ray binary 4U1626-67 performed during the BeppoSAX Science Verification Phase. We present the broad-band 0.1-100 keV pulse averaged spectrum, that is well fit by a two-component function: a 0.27 +/- 0.02 keV blackbody and an absorbed power law with a photon index of 0.89 +/- 0.02. A very deep and narrow absorption feature at 38 keV, attributable to electron cyclotron resonance, is clearly visible in the broad-band spectrum. It corresponds to a neutron star magnetic field strength of 3.3 x 10^{12} G. The 4U1626-67 pulse profiles show a dramatic dependance on energy: the transition between the low energy (E<10 keV) "bi-horned" shape to the high-energy (E>10 keV) sinusoidal profile is clearly visible in our data. The modulation index shows a monotonic increase with energy.Comment: 4 pages, 2 figures. Uses espcrc2.sty (included). To appear in Proceedings of "The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE

Observations of microglitches in HartRAO radio pulsars

A detailed observation of microglitch phenomenon in relatively slow radio pulsars is presented. Our analyses for these small amplitude jumps in pulse rotation frequency ($\nu$) and/or spin down rate ($\dot{\nu}$) combine the traditional manual detection method (which hinges on careful visual inspections of the residuals of pulse phase residuals) and a new, and perhaps more objective, automated search technique (which exploits the power of the computer, rather than the eyes, for resolving discrete events in pulsar spin parameters). The results of the analyses of a sample of 26 radio pulsars reveal that: (i) only 20 pulsars exhibit significant fluctuations in their arrival times to be considered suitable for meaningful microglitch analyses; (ii) a phenomenal 299 microglitch events were identified in $\nu$ and/or $\dot{\nu}$: 266 of these events were found to be simultaneously significant in $\nu$ and $\dot{\nu}$, while 19 and 14 were noticeable only in $\nu$ and $\dot{\nu}$, respectively; (iii) irrespective of sign, the microglitches have fractional sizes which cover about 3 orders of magnitude in $\nu$ and $\dot{\nu}$ ($10^{-11} < |\Delta{\nu}/\nu| < 2.0\times10^{-8}$ and $5.0\times10^{-5} < |\Delta{\dot{\nu}}/\dot{\nu}| < 2.0\times10^{-2}$) with median values as $0.78\times10^{-9}$ and $0.36\times10^{-3}$, respectively.Comment: 12 pages, 3 figures, 2 Tables. Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

Optical and infrared observations of the Crab Pulsar and its nearby knot

We study the spectral energy distribution (SED) of the Crab Pulsar and its nearby knot in the optical and in the infrared (IR) regime. We present high-quality UBVRIz, as well as adaptive optics JHK_sL' photometry, achieved under excellent conditions with the FORS1 and NAOS/CONICA instruments at the VLT. We combine these data with re-analyzed archival Spitzer Space Telescope data to construct a SED for the pulsar, and quantify the contamination from the knot. We have also gathered optical imaging data from 1988 to 2008 from several telescopes in order to examine the predicted secular decrease in luminosity. For the Crab Pulsar SED we find a spectral slope of alpha_nu = 0.27+-0.03 in the optical/near-IR regime, when we exclude the contribution from the knot. For the knot itself, we find a much redder slope of alpha_nu = -1.3 +- 0.1. Our best estimate of the average decrease in luminosity for the pulsar is 2.9+-1.6 mmag per year. We have demonstrated the importance of the nearby knot in precision measurements of the Crab Pulsar SED, in particular in the near-IR. We have scrutinized the evidence for the traditional view of a synchrotron self-absorption roll-over in the infrared, and find that these claims are unfounded. We also find evidence for a secular decrease in the optical light for the Crab Pulsar, in agreement with current pulsar spin-down models. However, although our measurements of the decrease significantly improve on previous investigations, the detection is still tentative. We finally point to future observations that can improve the situation significantly.Comment: For publication in A&

Pulsar timing irregularities and the imprint of magnetic field evolution

(Abridged) The rotational evolution of isolated neutron stars is dominated by the magnetic field anchored to the solid crust of the star. Assuming that the core field evolves on much longer timescales, the crustal field evolves mainly though Ohmic dissipation and the Hall drift, and it may be subject to relatively rapid changes with remarkable effects on the observed timing properties. We investigate whether changes of the magnetic field structure and strength during the star evolution may have observable consequences in the braking index, which is the most sensitive quantity to reflect small variations of the timing properties that are caused by magnetic field rearrangements. By performing axisymmetric, long-term simulations of the magneto-thermal evolution of neutron stars with state-of-the-art microphysical inputs, we find that the effect of the magnetic field evolution on the braking index can be divided into three qualitatively different stages depending on the age and the internal temperature: a first stage that may be different for standard pulsars (with n~3) or low field neutron stars that accreted fallback matter during the supernova explosion (systematically n<3); in a second stage, the evolution is governed by almost pure Ohmic field decay, and a braking index n>3 is expected; in the third stage, at late times, when the interior temperature has dropped to very low values, Hall oscillatory modes in the neutron star crust result in braking indices of high absolute value and both positive and negative signs. Models with strong (1e14 G) multipolar or toroidal components, even with a weak (~1e12 G) dipolar field are consistent with the observed trend of the timing properties.Comment: 7 pages, 5 figures, accepted for publication in Astronomy & Astrophysics (submitted July 24, 2012

Preoperative N-terminal pro-B-type natriuretic peptide and myocardial injury after stopping or continuing renin-angiotensin system inhibitors in noncardiac surgery: a prespecified analysis of a phase 2 randomised controlled multicentre trial.

BACKGROUND: Patients with elevated preoperative plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP >100 pg ml-1) experience more complications after noncardiac surgery. Individuals prescribed renin-angiotensin system (RAS) inhibitors for cardiometabolic disease are at particular risk of perioperative myocardial injury and complications. We hypothesised that stopping RAS inhibitors before surgery increases the risk of perioperative myocardial injury, depending on preoperative risk stratified by plasma NT-proBNP concentrations. METHODS: In a preplanned analysis of a phase 2a trial in six UK centres, patients ≥60 yr old undergoing elective noncardiac surgery were randomly assigned either to stop or continue RAS inhibitors before surgery. The pharmacokinetic profile of individual RAS inhibitors determined for how long they were stopped before surgery. The primary outcome, masked to investigators, clinicians, and patients, was myocardial injury (plasma high-sensitivity troponin-T ≥15 ng L-1 or a ≥5 ng L-1 increase, when preoperative high-sensitivity troponin-T ≥15 ng L-1) within 48 h after surgery. The co-exposures of interest were preoperative plasma NT-proBNP (100 pg ml -1) and stopping or continuing RAS inhibitors. RESULTS: Of 241 participants, 101 (41.9%; mean age 71 [7] yr; 48% females) had preoperative NT-proBNP >100 pg ml -1 (median 339 [160-833] pg ml-1), of whom 9/101 (8.9%) had a formal diagnosis of cardiac failure. Myocardial injury occurred in 63/101 (62.4%) subjects with NT-proBNP >100 pg ml-1, compared with 45/140 (32.1%) subjects with NT-proBNP 100 pg ml-1, myocardial injury rates were similar regardless of stopping (62.2%) or continuing (62.5%) RAS inhibitors (OR for stopping 0.98 [95% CI 0.44-2.22]). CONCLUSIONS: Stopping renin-angiotensin system inhibitors in lower-risk patients (preoperative NT-proBNP <100 pg ml -1) increased the likelihood of myocardial injury before noncardiac surgery

Spectral evolution and polarization of variable structures in the pulsar wind nebula of PSR B0540-69.3

We present high spatial resolution optical imaging and polarization observations of the PSR B0540-69.3 and its highly dynamical pulsar wind nebula (PWN) performed with HST, and compare them with X-ray data obtained with the Chandra X-ray Observatory. We have studied the bright region southwest of the pulsar where a bright "blob" is seen in 1999. We show that it may be a result of local energy deposition around 1999, and that the emission from this then faded away. Polarization data from 2007 show that the polarization properties show dramatic spatial variations at the 1999 blob position arguing for a local process. Several other positions along the pulsar-"blob" orientation show similar changes in polarization, indicating previous recent local energy depositions. In X-rays, the spectrum steepens away from the "blob" position, faster orthogonal to the pulsar-"blob" direction than along this axis of orientation. This could indicate that the pulsar-"blob" orientation is an axis along where energy in the PWN is mainly injected, and that this is then mediated to the filaments in the PWN by shocks. We highlight this by constructing an [S II]-to-[O III]-ratio map. We argue, through modeling, that the high [S II]/[O III] ratio is not due to time-dependent photoionization caused by possible rapid Xray emission variations in the "blob" region. We have also created a multiwavelength energy spectrum for the "blob" position showing that one can, to within 2sigma, connect the optical and X-ray emission by a single power law. We obtain best power-law fits for the X-ray spectrum if we include "extra" oxygen, in addition to the oxygen column density in the interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen is most naturally explained by the oxygen-rich ejecta of the supernova remnant. The oxygen needed likely places the progenitor mass in the 20 - 25 Msun range.Comment: Accepted by MNRAS on December 6th 2010, 18 pages, 15 figures. The article with full resolution figures is available here ftp://ftp.astro.su.se/pub/peter/papers/pwn0540_2010_corrected.pd