During the initial phase of the project, we focused on exploring the thermodynamics of compact stars as they are behind the potential production of relativistic jets in GRBs (WP1). Using a large number of parameterised equations of state (EOS), we have concluded that neutron stars are likely to have had an interior sound speed above the conformal limit, it (c_s)^2 = 1/3. These results align well with the estimated mass, radius, and tidal deformability obtained from gravitational-wave detectors. More recently, to assess the role played by neutrinos in launching a relativistic jet, we have completed neutrino moment based radiative-transfer code to simulate binary neutron-star mergers. This approach promises to provide reasonably accurate estimates of the energy and momentum losses from the post-merger remnant and and hence determine the physical conditions that could lead to the launching of a relativistic jet.
Further work performed by the JETSET team within WP1 includes a comprehensive study of fully general-relativistic hydrodynamics simulations of binary neutron stars using the V-QCD EOS, which incorporates the possibility of a quark phase appearing during the post-merger phase transition. This scenario could have significant implications for gravitational waves and the merger frequency. Additionally, using fully general-relativistic magnetohydrodynamics (GRMHD) simulations, we have investigated the role of the magnetic field in binary neutron star mergers, particularly in explaining mass ejection, jet launching, and the generation of short gamma-ray bursts. Our research explores the effects of turbulence and Kelvin-Helmholtz instabilities in the crust of neutron stars and the post-merger remnants. These latter study is very important to understand the formation channels of the large magnetic necessary to produce a relativistic jet in a GRB (WP2).
To gain a deeper understanding of particle acceleration within relativistic jets, we employed systematic particle-in-cell (PIC) numerical simulations to investigate the mechanisms behind particle acceleration and plasma heating at microscopic scales (WP1 and WP2). By updating the non-thermal electron and ion distribution functions, our results established a self-consistent connection between electron and proton temperatures, considering macroscopic plasma properties. Overall, our research efforts contribute to advancing the knowledge of jet dynamics in generic jets and shedding light on the processes of jet formation, propagation, and particle acceleration across the mass scale (WP4).
Finally, we analysed the jet dynamics in the M87 galaxy, specifically focusing on the active galactic nuclei, M87*, performing general-relativistic GRMHD simulations to explore the launching and propagation of the jet around a rotating supermassive black hole. We investigated the influence of the accretion disc model and magnetic field morphology, electron temperature, electron distribution function, and black hole rotation (WP1). In addition, we carried out general relativistic radiative transfer (GRRT) calculations to examine the multi-frequency electromagnetic emission. We tested theoretical models and compared them to observations in terms of their morphological features and across their wide electromagnetic spectrum (WP2 and WP5).
