Relativistic MHD simulations of short GRB jets in realistic post-merger environments

The first gravitational wave and electromagnetic (EM) observation of a merging binary neutron star (BNS) in 2017 demonstrated that such systems can launch powerful relativistic jets and, in turn, produce short gamma-ray bursts (SGRBs). However, the observational signatures of the emerging jet, including the multiwavelength afterglow signal produced by its interaction with the interstellar medium, could not provide direct information on the original post-merger dynamics, leaving behind key open questions on the jet launching mechanism and the nature of the merger remnant.

Different groups worldwide are investigating, via relativistic magnetohydrodynamic simulations, (i) the BNS merger process and remnant object formation, and (ii) how a jet launched by such a remnant object would propagate through the surrounding post-merger environment, acquiring the final structure that directly reflects in the EM emission. While the two aspects are typically studied separately, due to the different scales and physical ingredients involved, we presented in 2021 the first simulations of jets propagating through an environment that was directly imported from the outcome of a BNS merger simulation (Pavan et al. 2021).

Building on this pioneering work, we further advanced our description by considering magnetized systems and jets and realized a first fiducial simulation where the environment was imported from the longest magnetized BNS merger simulation (to date), presented in Ciolfi (2020a). This fiducial jet simulation will be presented in an upcoming publication (Pavan et al., in prep.).

In this project, we will start from the above fiducial model to perform another 12 jet simulations, realizing the first parameter study based on a consistent description combining BNS merger and jet propagation. In particular, we will consider initial data from two different BNS mergers and explore different jet launching times, luminosities, durations, and magnetizations.

As a result, we will assess the dependence of the final jet properties on these key physical parameters, also identifying possible trends and universalities. Moreover, we will have the opportunity to combine the final outcome with an advanced afterglow model, obtaining synthetic lightcurves to be directly compared with the rich dataset collected for the 2017 event. In turn, this will provide new constraints on the specific BNS merger remnant and jet launching conditions.