The recent multi-messenger observation of the GW-GRB 170817 has proven the gamma ray burst (GRB) coincidence with a gravitational wave produced by a neutron star binary coalescence, and opened a new window in astrophysics. Its subsequent detections obtained by several observatories across the entire electromagnetic spectrum were consistent with the radioactive decay of the nuclei freshly synthesized in the merger ejecta via the rapid neutron capture (r-process). On the other hand, the observational constraints on Galactic r-process elements abundances may point to the collapsars as the dominant sources of chemical enrichment in the Milky Way. The gamma ray bursts associated with these events are similarly powered by accretion onto a spinning black hole, which here has formed after the star’s core collapse, and is able to launch the relativistic jets. The possible astrophysical sites of r-process nucleosynthesis are in both cases the outflows launched from the black hole accretion disks, thus supporting the idea of universality of the central engine schema in short and long GRBs. We aim to make here further progress in understanding the properties of the GRB central engine, which can only be achieved by comparing the observations to accurate theoretical models that account for complex physics and many different scales. The fundamental interactions between elementary particles in the plasma, and proper description of microphysics in the accretion disk, further coupled with the wavelength of the magneto-rotational instability (MRI) turbulence, are on the first extreme limit. On the second extreme, there is the large scale jet propagation, and its interactions with the dynamical, neutron-rich ejecta, or with the stellar envelope, and ultimately with the interstellar medium where the jet terminates at a distance of thousands of millions of kilometers. Therefore, the spatial scales of the processes in interest differ here by almost 30 orders of magnitude. However the observational constraints for the quantities such as the jet power, its opening angle, or variability timescales, may only be obtained by the gamma-ray satellites for the large scale studies, the fundamental physics of the central engine operating at the jet base is governed by the general relativity, magnetodydrodynamics, and nuclear physics, that work on the smallest scales. This project will provide a consistent framework to model all scales of the gamma ray burst phenomenon, including the progenitor star, or binary system of compact stars, the central engine formed after the progenitor’s death, and the properties of relativistic jet expanding to large distances. This will be achieved by constructing the unique interface between numerical simulations working on GR MHD and large-scale hydrodynamics, that will then consistently be used to account for the feedback between the two scales. We will also construct a tool that verifies the probability and properties of a gravitational wave signal being coincident with a long gamma ray burst. The convincing detection of such event is still awaiting, but as the gravitational wave detectors reach their design sensitivity, it is essential to provide theoretical framework to maximize the potential of new discoveries. The same applies finally to the expected new detections of kilonova signals, whether coincident with the binary neutron star merger, or with the collapsars and long GRBs. The constraints obtained from observations will allow us to quantitatively study the physics of gamma ray bursts of various durations, and originating from a number of possible scenarios for their progenitor type and its pre-burst properties.
