Precise Timing and Phase-resolved Spectroscopy of the Young Pulsar J1617–5055 with NuSTAR

We report on a Nuclear Spectroscopic Telescope Array (NuSTAR) observation of the young, energetic pulsar PSR J1617–5055. Parkes Observatory 3 GHz radio observations of the pulsar (taken about 7 yr before the NuSTAR observations) are also reported here. NuSTAR detected pulsations at a frequency of f ≈ 14.4 Hz (P ≈ 69.44 ms) and, in addition, the observation was long enough to measure the source’s frequency derivative, f ̇ ≈ − 2.8 × 10 − 11 Hz s−1. We find that the pulsar shows one peak per period at both hard X-ray and radio wavelengths, but that the hard X-ray pulse is broader (having a duty cycle of ∼0.7), than the radio pulse (having a duty cycle of ∼0.08). Additionally, the radio pulse is strongly linearly polarized. J1617's phase-integrated hard X-ray spectrum is well fit by an absorbed power-law model, with a photon index Γ = 1.59 ± 0.02. The hard X-ray pulsations are well described by three Fourier harmonics, and have a pulsed fraction that increases with energy. We also fit the phase-resolved NuSTAR spectra with an absorbed power-law model in five phase bins and find that the photon index varies with phase from Γ = 1.52 ± 0.03 at phases around the flux maximum to Γ = 1.79 ± 0.06 around the flux minimum. Last, we compare our results with other pulsars whose magnetospheric emission is detected at hard X-ray energies and find that, similar to previous studies, J1617's hard X-ray properties are more similar to the MeV pulsars than the GeV pulsars.

Wide-angle Reconfigurable Refraction by Silicon Fourier Metasurfaces

We design metasurfaces based on silicon films with smooth relief described by several Fourier harmonics and study their ability to redirect the refracted light over a wide angular range controlled by subtle variations of the optical setup. We use semi-analytical approach based on the Rayleigh hypothesis as well as full-scale numerical solutions to optimize the relief shape. To illustrate the reconfigurability potential, we design metasurfaces efficiently redirecting the refracted light from 83° to −73° with respect to the normal, when the angle of incidence is varied from 0° to 2°, and from 80° to −74°, when the substrate permittivity is altered from 2.3 to 2.2.

Weak plasmon modes in periodic structures for terahertz detection and amplification

Weak plasmon modes in periodic structures with a two-dimensional electron gas without an inversion center are studied theoretically. The asymmetry of the electric field and Fourier harmonics of weak plasmon modes can lead to the excitation of a travelling plasmon by an electromagnetic wave normally incident on the structure and to the appearance of nonlinear effects leading to the rectification of the incident radiation. The low radiation damping of weak plasmon modes can be used to increase the efficiency of terahertz plasmon amplifiers.

Identificación de stocks de Engraulis ringens en Chile utilizando morfometría de otolitos

Anchovy (Engraulis ringens) population units were analyzed in three zones off the coast of Chile: 1: Arica-Iquique, 2: Coquimbo and 3: Talcahuano-Valdivia from samples obtaineds during the 2012 spawning season. We used 50 left sagittae otoliths from each zone to perform a morphometric analysis, which included basic measurements, shape indexes and contour analysis (elliptical Fourier analysis). A MANOVA and Tukey multiple comparison analyses, applied on basic measures and shape indexes showed significant differences between zone 3 and zones 1 and 2. A classification by Canonical Discriminant analysis of elliptical Fourier harmonics, indicated significant differences among zones. It is concluded, therefore, that otolith shape analysis could be used to discriminate population units of Engraulis ringens. Better results were achieved using elliptic Fourier coefficients than using only shape indices.

A systematic study of soft X-ray pulse profiles of magnetars in quiescence

Magnetars are neutron stars with extremely high surface magnetic fields. They show diverse X-ray pulse profiles in the quiescent state. We perform a systematic Fourier analysis of their soft X-ray pulse profiles. We find that most magnetars have a single-peaked profile and hence have low amplitudes of the second Fourier harmonics (A2). On the other hand, the pulsed fraction (PF) spreads over a wide range. We compared the results with theoretical profiles assuming various surface hotspot asymmetries, viewing geometries, and beaming functions. We found that a single value of the intensity ratio r between two antipodal hotspots is unable to reproduce the observed distribution of A2 and PF for all magnetars. The inferred r is probably anticorrelated with the thermal luminosity, implying that high-luminosity magnetars tend to have two symmetric hotspots. Our results are consistent with theoretical predictions, for which the existence of an evolving toroidal magnetic field breaks the symmetry of the surface temperature.