983 research outputs found

    Evidence for a Binary Companion to the Central Compact Object 1E 1207.4-5209

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    Unique among neutron stars, 1E 1207.4-5209 is an X-ray pulsar with a spin period of 424 ms that contains at least two strong absorption features in its energy spectrum. This neutron star has been identified as a member of the radio-quiet compact central objects in supernova remnants. It has been found that 1E 1207.4-5209 is not spinning down monotonically suggesting that this neutron star undergoes strong, frequent glitches, contains a fall-back disk, or possess a binary companion. Here, we report on a sequence of seven XMM-Newton observations of 1E 1207.4-5209 performed during a 40 day window in June/July 2005. Due to unanticipated variance in the phase measurements beyond the statistical uncertainties, we could not identify a unique phase-coherent timing solution. The three most probable timing solutions give frequency time derivatives of +0.9, -2.6, and +1.6 X 10^(-12) Hz/s (listed in descending order of significance). We conclude that the local frequency derivative during our XMM-Newton observing campaign differs from the long-term spin-down rate by more than an order of magnitude, effectively ruling out glitch models for 1E 1207.4-5209. If the long-term spin frequency variations are caused by timing noise, the strength of the timing noise in 1E 1207.4-5209 is much stronger than in other pulsars with similar period derivatives. Therefore, it is highly unlikely that the spin variations are caused by the same physical process that causes timing noise in other isolated pulsars. The most plausible scenario for the observed spin irregularities is the presence of a binary companion to 1E 1207.4-5209. We identified a family of orbital solutions that are consistent with our phase-connected timing solution, archival frequency measurements, and constraints on the companions mass imposed by deep IR and optical observations.Comment: 8 pages, 4 figures. To be published in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface" (April 24-28, 2006) - eds. D. Page, R. Turolla & S. Zan

    High-precision determination of the critical exponents for the lambda-transition of 4He by improved high-temperature expansion

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    We determine the critical exponents for the XY universality class in three dimensions, which is expected to describe the λ\lambda-transition in 4{}^4He. They are obtained from the analysis of high-temperature series computed for a two-component λϕ4\lambda\phi^4 model. The parameter λ\lambda is fixed such that the leading corrections to scaling vanish. We obtain ν=0.67166(55)\nu = 0.67166(55), γ=1.3179(11)\gamma = 1.3179(11), α=0.0150(17)\alpha=-0.0150(17). These estimates improve previous theoretical determinations and agree with the more precise experimental results for liquid Helium.Comment: 8 pages, revte

    A two-mass expanding exact space-time solution

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    In order to understand how locally static configurations around gravitationally bound bodies can be embedded in an expanding universe, we investigate the solutions of general relativity describing a space-time whose spatial sections have the topology of a 3-sphere with two identical masses at the poles. We show that Israel junction conditions imply that two spherically symmetric static regions around the masses cannot be glued together. If one is interested in an exterior solution, this prevents the geometry around the masses to be of the Schwarzschild type and leads to the introduction of a cosmological constant. The study of the extension of the Kottler space-time shows that there exists a non-static solution consisting of two static regions surrounding the masses that match a Kantowski-Sachs expanding region on the cosmological horizon. The comparison with a Swiss-Cheese construction is also discussed.Comment: 15 pages, 5 figures. Replaced to match the published versio

    25th-order high-temperature expansion results for three-dimensional Ising-like systems on the simple cubic lattice

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    25th-order high-temperature series are computed for a general nearest-neighbor three-dimensional Ising model with arbitrary potential on the simple cubic lattice. In particular, we consider three improved potentials characterized by suppressed leading scaling corrections. Critical exponents are extracted from high-temperature series specialized to improved potentials, obtaining γ=1.2373(2)\gamma=1.2373(2), ν=0.63012(16)\nu=0.63012(16), α=0.1096(5)\alpha=0.1096(5), η=0.03639(15)\eta=0.03639(15), β=0.32653(10)\beta=0.32653(10), δ=4.7893(8)\delta=4.7893(8). Moreover, biased analyses of the 25th-order series of the standard Ising model provide the estimate Δ=0.52(3)\Delta=0.52(3) for the exponent associated with the leading scaling corrections. By the same technique, we study the small-magnetization expansion of the Helmholtz free energy. The results are then applied to the construction of parametric representations of the critical equation of state, using a systematic approach based on a global stationarity condition. Accurate estimates of several universal amplitude ratios are also presented.Comment: 40 pages, 15 figure

    Quantum Breaking Time Scaling in the Superdiffusive Dynamics

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    We show that the breaking time of quantum-classical correspondence depends on the type of kinetics and the dominant origin of stickiness. For sticky dynamics of quantum kicked rotor, when the hierarchical set of islands corresponds to the accelerator mode, we demonstrate by simulation that the breaking time scales as τ(1/)1/μ\tau_{\hbar} \sim (1/\hbar)^{1/\mu} with the transport exponent μ>1\mu > 1 that corresponds to superdiffusive dynamics. We discuss also other possibilities for the breaking time scaling and transition to the logarithmic one τln(1/)\tau_{\hbar} \sim \ln(1/\hbar) with respect to \hbar

    Diagnosing complex regional pain syndrome using an electronic nose, a pilot study

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    Objective: Complex regional pain syndrome (CRPS)is a complication after surgery or trauma and is characterized by a continuing regional pain in a distal extremity. The pain is disproportionate in severity and duration in relation to the preceding trauma. Currently, the diagnosis is based on the patients’signs and symptoms. There is no objective clinically applicable test available to confirm the diagnosis of CRPS, however this could contribute to a more reliable and valid diagnosis. Since the treatment of CRPS differs from that of other types of pain this could thereby lead to earlier and (more) appropriate treatment and possibly to lower medical costs. The Aeonose™ is a diagnostic test device which detects volatile organic profiles in exhaled air. Exhaled breath analysis using an electronic nose has been successfully applied to differentiate between sick and healthy persons for various indications. This study was a feasibility study in which we investigated whether the Aeonose™ is able to

    UV emission from young and middle-aged pulsars: Connecting X-rays with the optical

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    We present the UV spectroscopy and timing of three nearby pulsars (Vela, B0656+14 and Geminga) recently observed with the Space Telescope Imaging Spectrograph. We also review the optical and X-ray properties of these pulsars and establish their connection with the UV properties. We show that the multiwavelengths properties of neutron stars (NSs) vary significantly within the sample of middle-aged pulsars. Even larger differences are found between the thermal components of Ge-minga and B0656+14 as compared to those of radio-quiet isolated NSs. These differences could be attributed to different properties of the NS surface layers.Comment: To appear in Astrophysics and Space Science, Proceedings of "Isolated Neutron Stars: from the Interior to the Surface", eds. D. Page, R. Turolla and S. Zane; 10 pages, 4 figures, 3 table
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