Pulsar timing irregularities and the imprint of magnetic field evolution

Context. 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. Aims. We investigate whether changes of the magnetic field structure and strength during the star evolution may have observable consequences in the braking index n. This is the most sensitive quantity to reflect small variations of the timing properties that are caused by magnetic field rearrangements. Methods. We performed axisymmetric, long-term simulations of the magneto-thermal evolution of neutron stars with state-of-the-art microphysical inputs to calculate the evolution of the braking index. Relatively rapid magnetic field modifications can be expected only in the crust of neutron stars, where we focus our study. Results. 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 a high absolute value and both positive and negative signs. Conclusions. Current magneto-thermal evolution models predict a large contribution to the timing noise and, in particular, to the braking index, from temporal variations of the magnetic field. Models with strong (≳ 1014 G) multipolar or toroidal components, even with a weak (~1012 G) dipolar field are consistent with the observed trend of the timing properties.

The outburst decay of the low magnetic field magnetar SGR 0418+5729

We report on the long-term X-ray monitoring of the outburst decay of the low magnetic field magnetar SGR 0418+5729 using all the available X-ray data obtained with RXTE, Swift, Chandra, and XMM-Newton observations from the discovery of the source in 2009 June up to 2012 August. The timing analysis allowed us to obtain the first measurement of the period derivative of SGR 0418+5729: ˙ P = 4(1) × 10−15 s s−1, significant at a ∼3.5σ confidence level. This leads to a surface dipolar magnetic field of Bdip 6 × 1012 G. This measurement confirms SGR 0418+5729 as the lowest magnetic field magnetar. Following the flux and spectral evolution from the beginning of the outburst up to ∼1200 days, we observe a gradual cooling of the tiny hot spot responsible for the X-ray emission, from a temperature of ∼0.9 to 0.3 keV. Simultaneously, the X-ray flux decreased by about three orders of magnitude: from about 1.4 × 10−11 to 1.2 × 10−14 erg s−1 cm−2. Deep radio, millimeter, optical, and gamma-ray observations did not detect the source counterpart, implying stringent limits on its multi-band emission, as well as constraints on the presence of a fossil disk. By modeling the magneto-thermal secular evolution of SGR 0418+5729, we infer a realistic age of ∼550 kyr, and a dipolar magnetic field at birth of ∼1014 G. The outburst characteristics suggest the presence of a thin twisted bundle with a small heated spot at its base. The bundle untwisted in the first few months following the outburst, while the hot spot decreases in temperature and size. We estimate the outburst rate of low magnetic field magnetars to be about one per year per galaxy, and we briefly discuss the consequences of such a result in several other astrophysical contexts.

Is SGR 0418+5729 indeed a waning magnetar?

SGR 0418+5729 is a transient soft gamma-ray repeater which underwent a major outburst in 2009 June, during which the emission of short bursts was observed. Its properties appeared quite typical of other sources of the same class until long-term X-ray monitoring failed to detect any period derivative. The present upper limit on P implies that the surface dipole field is Bp lsim 7.5 × 1012 G, well below those measured in other soft gamma-ray repeaters (SGRs) and in the Anomalous X-ray Pulsars (AXPs), a group of similar sources. Both SGRs and AXPs are currently believed to be powered by ultra-magnetized neutron stars (magnetars, Bp ≈ 1014-1015 G). SGR 0418+5729 hardly seems to fit in such a picture. We show that the magneto-rotational properties of SGR 0418+5729 can be reproduced if this is an aged magnetar, ≈1 Myr old, which experienced substantial field decay. The large initial toroidal component of the internal field required to match the observed properties of SGR 0418+5729 ensures that crustal fractures, and hence bursting activity, can still occur at the present time. The thermal spectrum observed during the outburst decay is compatible with the predictions of a resonant Compton scattering model (as in other SGRs/AXPs) if the field is low and the magnetospheric twist is moderate.

Binderless thin films of zeolite-templated carbon electrodes useful for electrochemical microcapacitors with ultrahigh rate performance

Controlled nanozeolite deposits are prepared by electrochemical techniques on a macroporous carbon support and binderless thin film electrodes of zeolite-templated carbon are synthesized using the deposits as templates. The obtained film electrodes exhibit extremely high area capacitance (10–12 mF cm−2) and ultrahigh rate capability in a thin film capacitor.

España: de los impactos de la crisis a las movilizaciones de protesta

El sur de Europa está experimentando una crisis económica de una intensidad y duración desconocida en la memoria de muchas generaciones. El impacto se agrava al producirse tras un breve período de bonanza económica y expansión del consumo, cuyo efecto a medio plazo fue endeudar fuertemente a las clases medias y populares. La destrucción acelerada del empleo ha cambiado el panorama social, al producir una emergente contestación social, consecuencia, entre otros motivos, de los abusos normativos que protegen al sistema financiero. Estas tensiones se producen en un contexto donde las instituciones políticas experimentan una crisis de credibilidad como fruto de la corrupción, la financiación ilegal de partidos y los lucros y privilegios personales de los políticos. Por efecto de la crisis económica la sensibilidad social a estos casos se ha incrementado. La bifurcación de la crisis económica en crisis social y política, y la interacción entre éstas define la movilización sociopolítica en España. Movilización en las calles, pero también cambios en las posiciones adoptadas ante el sistema de partidos y la práctica democrática en conjunto. Las críticas al modo de hacer política en España han llevado, como reflexión popular colectiva, a cuestionar el concepto de democracia como una simple expresión formal de reglas y procedimientos. En la actualidad esta situación puede transformar profundamente el sistema político español. Primero como consecuencia de los movimientos de resiliencia democrática que buscan nuevas expresiones políticas. Y segundo, dada la difusión de una alienación política que enajena a los ciudadanos del actual sistema de partidos.

Numerical resolution of Emden's equation using Adomian polynomials

Purpose: In this paper the authors aim to show the advantages of using the decomposition method introduced by Adomian to solve Emden's equation, a classical non‐linear equation that appears in the study of the thermal behaviour of a spherical cloud and of the gravitational potential of a polytropic fluid at hydrostatic equilibrium. Design/methodology/approach: In their work, the authors first review Emden's equation and its possible solutions using the Frobenius and power series methods; then, Adomian polynomials are introduced. Afterwards, Emden's equation is solved using Adomian's decomposition method and, finally, they conclude with a comparison of the solution given by Adomian's method with the solution obtained by the other methods, for certain cases where the exact solution is known. Findings: Solving Emden's equation for n in the interval [0, 5] is very interesting for several scientific applications, such as astronomy. However, the exact solution is known only for n=0, n=1 and n=5. The experiments show that Adomian's method achieves an approximate solution which overlaps with the exact solution when n=0, and that coincides with the Taylor expansion of the exact solutions for n=1 and n=5. As a result, the authors obtained quite satisfactory results from their proposal. Originality/value: The main classical methods for obtaining approximate solutions of Emden's equation have serious computational drawbacks. The authors make a new, efficient numerical implementation for solving this equation, constructing iteratively the Adomian polynomials, which leads to a solution of Emden's equation that extends the range of variation of parameter n compared to the solutions given by both the Frobenius and the power series methods.

Composición Arquitectónica 5 y 6

La presente Memoria culmina el trabajo colaborativo del área de conocimiento de Composición Arquitectónica por lo que respecta a las materias de Grado en (Fundamentos en) Arquitectura, al haber definido sus contenidos, sus métodos de aprendizaje y sus sistemas de evaluación para el conjunto de la titulación. Ahora se concretan las dos últimas asignaturas de 5º curso: CA5 y CA6. Por un lado está CA5, cuyo eje fundamental es la definición de criterios para el ejercicio de la crítica de arquitectura, una vez que se ha construido una base de información histórica y teórica en los estudiantes a lo largo de cuatro cursos. Una crítica entendida tanto como sistema de contextualización sobre las obras ejecutadas (del presente o del pasado) y, a la vez, como marco de referencia para someter a evaluación las soluciones que se proponen desde proyecto (desde el presente hacia el futuro). Así pues, crítica entendida como herramienta de análisis tanto como de prospección. Por otro lado está CA6, en la que el eje fundamental es la intervención sobre el patrimonio arquitectónico, sea o no monumental, entendido como una realidad ineludible pues gran parte del trabajo de los arquitectos transita sobre preexistencias en sus muy diversos grados.

Are pulsars born with a hidden magnetic field?

The observation of several neutron stars in the centre of supernova remnants and with significantly lower values of the dipolar magnetic field than the average radio-pulsar population has motivated a lively debate about their formation and origin, with controversial interpretations. A possible explanation requires the slow rotation of the protoneutron star at birth, which is unable to amplify its magnetic field to typical pulsar levels. An alternative possibility, the hidden magnetic field scenario, considers the accretion of the fallback of the supernova debris on to the neutron star as responsible for the submergence (or screening) of the field and its apparently low value. In this paper, we study under which conditions the magnetic field of a neutron star can be buried into the crust due to an accreting, conducting fluid. For this purpose, we consider a spherically symmetric calculation in general relativity to estimate the balance between the incoming accretion flow and the magnetosphere. Our study analyses several models with different specific entropy, composition, and neutron star masses. The main conclusion of our work is that typical magnetic fields of a few times 1012 G can be buried by accreting only 10−3–10−2 M⊙, a relatively modest amount of mass. In view of this result, the central compact object scenario should not be considered unusual, and we predict that anomalously weak magnetic fields should be common in very young (< few kyr) neutron stars.

Factores que intervienen en el rendimiento académico universitario: un estudio de caso

Conocer los factores intervinientes en el rendimiento académico de los estudiantes es de vital importancia para mejorar el proceso de enseñanza-aprendizaje y la calidad universitaria. Esta investigación busca identificar los posibles factores que intervienen en el rendimiento académico de los estudiantes universitarios del grado en Arquitectura Técnica de la Universidad de Alicante. El estudio pretende determinar el poder explicativo y predictivo de nueve variables para pronosticar el rendimiento académico de los estudiantes mediante regresión lineal múltiple. Se ha identificado que seis de las variables estudiadas son estadísticamente significativas y que dos de ellas tienen una gran influencia sobre el rendimiento académico.