Getti di Lampi di Raggi Gamma Brevi prodotti dalla Coalescenza di Stelle di Neutroni

Short gamma-ray bursts (SGRBs) are flashes of high-energy (sub-MeV) radiation lasting for less than ∼ 2 s, most likely generated as a result of compact binary mergers. The multi-messenger event of August 2017, during which gravitational waves from a binary neutron star (BNS) merger were detected jointly with the SGRB known as GRB 170817A, has demonstrated that such bursts can indeed be produced by coalescing BNSs. Moreover, it has shown that a collimated ultra-relativistic jet was launched by the merger remnant, and powered the SGRB emission by imprinting its angular properties and energetics on the latter. Currently, theoretical investigation of events such as GRB 170817A builds on (i) general-relativistic BNS merger simulations to self-consistently reproduce the launching of an incipient SGRB jet, and (ii) special-relativistic simulations to follow the evolution of the jet on much larger time and spatial scales, until the final properties of the outflow that can be directly probed with the observations are defined. Such a twofold set of simulations, however, presents a major limitation: for the jet evolution on large scales carried out in (ii), idealized hand-made surrounding environments are typically adopted to set the initial conditions, without any direct connection with the realistic distributions of matter and magnetic field resulting from (i). In this Thesis work, we overcome such a limitation by performing the first special-relativistic SGRB jet simulations employing environments directly imported from the outcome of general-relativistic BNS merger simulations. Our jet simulations, carried out in three dimensions, and both in the absence and in presence of magnetic fields, allow us to investigate the role of such realistic environments in the dynamical evolution of SGRB jets and to unveil, for the first time, their crucial importance in shaping the final jet angular structure and energetics, and thus the associated electromagnetic signatures. Such an achievement marks a fundamental step toward an end-to-end description of SGRB events, connecting in a consistent way properties of the system at the time of merger with those characterizing the electromagnetic emission phase, probed by observations. The work presented here paves the way for an in-depth exploration of the relevant parameter space (already on the way) and for a more solid interpretation of GRB 170817A and similar events in the future.