Resonant shattering of neutron star crusts

The resonant excitation of neutron star (NS) modes by tides is investigated as a source of short gamma-ray burst (SGRB) precursors. We find that the driving of a crust-core interface mode can lead to shattering of the NS crust, liberating ～10{46}-10{47} erg of energy seconds before the merger of a NS-NS or NS-black-hole binary. Such properties are consistent with Swift/BAT detections of SGRB precursors, and we use the timing of the observed precursors to place weak constraints on the crust equation of state. We describe how a larger sample of precursor detections could be used alongside coincident gravitational wave detections of the inspiral by Advanced LIGO class detectors to probe the NS structure. These two types of observations nicely complement one another, since the former constrains the equation of state and structure near the crust-core boundary, while the latter is more sensitive to the core equation of state.     

Statistics of magnetic noise in neutron star crusts

The neutron star crust magnetodynamics is demonstrated to exhibit erratic jumps at the fields corresponding to a sharp change of nuclide magnetic moments induced by quantization effects. Such a noise originates from magnetic avalanches and shows intensity and statistical properties which are favorably compared to the burst activity of soft gamma repeaters.     

Specific heat of the superfluid neutron matter in neutron star crusts

By means of X-γ andγ-γ coincidence measurements of the³⁵Cl+⁵⁸Ni reaction products, 38γ lines have been identified to be in coincidence with KX(Tc)-rays and assigned to the decay of⁹⁰Ru. Its half-life of 11±3 s has been deduced from the 154.6 keVγ-decay. The result supports our previous identification of⁹⁰Ru produced in the same reactions.     

Pinning mechanism and vortex trap region in neutron star crusts

We investigate, in the framework of a trap/discharge vortex mechanism for pulsars glitches, different hypoteses in order to explain the origin as well as the behavior of the vortex—capacitor zone in the crust of a neutron star. We provide different scenarios depending of temperature and crustal structures.     

Pinning mechanism and vortex trap region in neutron star crusts

We investigate, in the framework of a trap/discharge vortex mechanism for pulsars glitches, different hypoteses in order to explain the origin as well as the behavior of the vortex-capacitor zone in the crust of a neutron star. We provide different scenarios depending of temperature and crustal structures.     

Thermal conduction across neutron star crusts and cooling of young neutron stars

We calculate thermal conduction times in the crust and core of a neutron star and find that for certain neutron star models the surface remains thermally isolated from the core at initial times. The surface temperature of a few hundred year old neutron star in these models can be insensitive to the presence of a pion-condensed core and might well be within the limits of observability of the HEAO satellite which can help to distinguish between different neutron star models.     

Symmetry energy,unstable nuclei and neutron star crusts

We present an upgraded review of our microscopic investigation on the single-particle properties and the EOS of isospin asymmetric nuclear matter within the framework of the Brueckner theory extended to include a microscopic three-body force. We pay special attention to the discussion of the three-body force effect and the comparison of our results with the predictions by other ab initio approaches. Three-body force is shown to be necessary for reproducing the empirical saturation properties of symmetric nuclear matter within nonrelativistic microscopic frameworks, and also for extending the hole-line expansion to a wide density range. The three-body force effect on nuclear symmetry energy is repulsive, and it leads to a significant stiffening of the density dependence of symmetry energy at supra-saturation densities. Within the Brueckner approach, the three-body force affects the nucleon s.p. potentials primarily via its rearrangement contribution which is strongly repulsive and momentum-dependent at high densities and high momenta. Both the rearrangement contribution induced by the three-body force and the effect of ground-state correlations are crucial for predicting reliably the single-particle properties within the Brueckner framework.     

Shell structure of nuclei in strong magnetic fields in neutron star crusts

By employing Strutinsky's treatment we demonstrate that the magnetic field gives rise to a phase shift of the shell oscillations in nuclear masses. The proton orbital magnetism is shown to enhance the nuclear shell effect especially when the field influence is comparable to the spin-orbit coupling. The magnetic field of the strength scale B approximately 10(16)-10(17) G is found to shift significantly the nuclear magic numbers of the iron region towards smaller mass numbers.     

Neutron superfluidity and unusual nuclear shapes in neutron stars crusts

We calculate in the frame-work of a semiclassical model the neutron superfluidity in the crust of neutron stars, accounting for the presence of unusual nuclear shape. We have found a marked spatial anisotropy in the calculated pairing energy gap.     

Relativistic equation of state of nuclear matter for supernova and neutron star

We construct the equation of state (EOS) of nuclear matter using the relativistic mean field (RMF) theory in the wide density, temperature range with various proton fractions for the use of supernova simulation and the neutron star calculations. We first construct the EOS of homogeneous nuclear matter. We use then the Thomas-Fermi approximation to describe inhomogeneous matter, where heavy nuclei are formed together with free nucleon gas. We discuss the results on free energy, pressure and entropy in the wide range of astrophysical interest. As an example, we apply the resulting EOS on the neutron star properties by using the Oppenheimer-Volkoff equation.     

Unified neutron star EOSs and neutron star structures in RMF models

In the framework of the Thomas-Fermi approximation, we systematically study the EOSs and microscopic structures of neutron star matter in a vast density range with n_b ≈ 10⁻¹⁰-2 fm⁻³, where various covariant density functionals are adopted, i.e., those with nonlinear self couplings (NL3, PK1, TM1, GM1, MTVTC) and density-dependent couplings (DD-LZ1, DDME-X, PKDD, DD-ME2, DD2, TW99). It is found that the EOSs generally coincide with each other at n_b ≲ 10⁻⁴ fm⁻³ and 0.1 fm⁻³ ≲ n_b ≲ 0.3 fm⁻³, while in other density regions they are sensitive to the effective interactions between nucleons. By adopting functionals with a larger slope of symmetry energy L, the curvature parameter K_sym and neutron drip density generally increases, while the droplet size, proton number of nucleus, core-crust transition density, and onset density of non-spherical nuclei, decrease. All functionals predict neutron stars with maximum masses exceeding the two-solar-mass limit, while those of DD2, DD-LZ1, DD-ME2, and DDME-X predict optimum neutron star radii according to the observational constraints. Nevertheless, the corresponding skewness coefficients J are much larger than expected, while only the functionals MTVTC and TW99 meet the start-of-art constraints on J. More accurate measurements on the radius of PSR J0740 + 6620 and the maximum mass of neutron stars are thus essential to identify the functional that satisfies all constraints from nuclear physics and astrophysical observations. Approximate linear correlations between neutron stars' radii at M = 1.4M_⊙ and 2M_⊙, the slope L and curvature parameter K_sym of symmetry energy are observed as well, which are mainly attributed to the curvature-slope correlations in the functionals adopted here. The results presented here are applicable for investigations of the structures and evolutions of compact stars in a unified manner.     

Connecting neutron star observations to three-body forces in neutron matter and to the nuclear symmetry energy

Using a phenomenological form of the equation of state of neutron matter near the saturation density which has been previously demonstrated to be a good characterization of quantum Monte Carlo simulations, we show that currently available neutron star mass and radius measurements provide a significant constraint on the equation of state of neutron matter. At higher densities we model the equation of state by using polytropes and a quark matter model. We show that observations offer an important constraint on the strength of the three-body force in neutron matter, and thus some theoretical models of the three-body force may be ruled out by currently available astrophysical data. In addition, we obtain an estimate of the symmetry energy of nuclear matter and its slope that can be directly compared to the experiment and other theoretical calculations.     

Time-of-flight neutron spectrometer for micro sample studies under high pressure

Abstract

A new neutron spectrometer for investigations of elastic and inelastic neutron scattering on polycrystal microsamples under high pressure in diamond and sapphire anvils cells is described. The spectrometer is operating at the IBR-2 pulsed reactor at JINR. The time-of-flight method and ring-shaped multicounter detector are used to register the scattered neutrons. Parameters and methodical peculiarities of the device and the examples of experimental studies are given.     

Magnetic equation for a rotating neutron star

The magnetic configuration in the plasma-sphere surrounding a neutron star is described in terms of a model equation that is constructed to be valid from the surface of the star to distances of the order of the light speed cylinder and beyond. Significant asymptotic solutions of this equation, that are valid in limited regions around the star, are presented.