[en] The induced gravitational collapse paradigm explains a class of energetic, $E_{\mathrm{i}\mathrm{s}\mathrm{o}}\gtrsim <!--\; ???\; -->{10}^{52}$ erg, long-duration gamma-ray bursts (GRBs) associated with Ic supernovae, recently named binary-driven hypernovae. The progenitor is a tight binary system formed of a carbon–oxygen (CO) core and a neutron star (NS) companion. The supernova ejecta of the exploding CO core trigger a hypercritical accretion process onto the NS, which reaches the critical mass in a few seconds, and gravitationally collapses to a black hole, emitting a GRB. In our previous simulations of this process, we adopted a spherically symmetric approximation to compute the features of the hypercritical accretion process. We here present the first estimates of the angular momentum transported by the supernova ejecta, $L_{\mathrm{a}\mathrm{c}\mathrm{c}},$ and perform numerical simulations of the angular momentum transfer to the NS during the hyperaccretion process in full general relativity. We show that the NS (1) reaches either the mass-shedding limit or the secular axisymmetric instability in a few seconds depending on its initial mass, (2) reaches a maximum dimensionless angular momentum value, ${[cJ/({GM}^2)]}_{\mathrm{m}\mathrm{a}\mathrm{x}}\approx <!--\; ???\; -->0.7$, and (3) can support less angular momentum than the one transported by supernova ejecta, $L_{\mathrm{a}\mathrm{c}\mathrm{c}}><!--\; >\; -->J_{\mathrm{N}\mathrm{S},\mathrm{m}\mathrm{a}\mathrm{x}},$ hence there is an angular momentum excess that necessarily leads to jetted emission.

[en] The new era of multimessenger astrophysics requires the capability of studying different aspects of the evolution of compact objects. In particular, the merger of neutron star binaries is a strong source of gravitational waves and electromagnetic radiation, from radio to γ-rays, as demonstrated by the detection of GW170817 and its electromagnetic counterparts. In order to understand the physical mechanisms involved in such systems, it is necessary to employ fully general relativistic magnetohydrodynamic (GRMHD) simulations able to include the effects of a composition and temperature dependent equation of state describing neutron star matter as well as neutrino emission and reabsorption. Here, we present our new code named Spritz that solves the GRMHD equations in 3D Cartesian coordinates and on a dynamical spacetime. The code can support tabulated equations of state, taking into account finite temperature effects and allowing for the inclusion of neutrino radiation. In this first paper, we present the general features of the code and a series of tests performed in special and general relativity to assess the robustness of the basic GRMHD algorithms implemented. Among these tests, we also present the first comparison between a non-staggered and a staggered formulation of the vector potential evolution, which is used to guarantee the divergence-less character of the magnetic field. With respect to other publicly available GRMHD codes, Spritz combines the robust approach of a staggered formulation of the vector potential together with the use of an equation of state driver (EOS_Omni) that can allow the code to use finite temperature equations of state. A next version of the code will fully test the EOS_Omni driver by coupling it with a neutrino leakage scheme. (paper)

[en] We here present a new version of the publicly available general relativistic magnetohydrodynamic (GRMHD) code Spritz, which now includes an approximate neutrino leakage scheme able to handle neutrino cooling and heating. The leakage scheme is based on the publicly available ZelmaniLeak code, with a few modifications in order to properly work with Spritz. We discuss the involved equations, physical assumptions, and implemented numerical methods, along with a large battery of general relativistic tests performed with and without magnetic fields. Our tests demonstrate the correct implementation of the neutrino leakage scheme, paving the way for further improvements of our neutrino treatment and the first application to magnetized binary neutron star mergers. We also discuss the implementation in the Spritz code of high-order methods for a more accurate evolution of hydrodynamical quantities. (paper)

[en] We summarize the recent results on the physics and astrophysics of neutron stars presented in the Second ICRANet César Lattes Meeting in 2015