High-energy multimessenger emission from jets propagating in neutron star merger ejecta

Neutron star (NS) mergers are amongst the most promising multimessenger sources in the Universe, as demonstrated by the coincident detection of gravitational waves (GWs) and multi-wavelength electromagnetic (EM) radiation in the GW170817 event. Moreover, they have been proposed as potential sources of ultra-high-energy cosmic rays and high-energy neutrinos. Short-duration gamma-ray bursts (sGRBs) are thought to originate from relativistic jets launched by NS merger remnants, but there are still uncertainties about the exact nature of such a remnant: it may be a promptly formed black hole (BH), a hypermassive NS that later collapses to a BH, or even a stable NS. The jet launching mechanism and its properties may differ for each scenario, and so do the observable phenomena. In this work, we investigate jet propagation in realistic merger ejecta obtained from numerical simulations with the General-Relativistic Hydrodynamic (GRHD) code THC_M1. We construct a semi-analytical jet propagation model to perform a comprehensive analysis of the role of the central engine properties on jet propagation, its interplay with the merger ejecta, and the cocoon formed by such an interaction. We examine the conditions for which the jet successfully breaks out and/or gets collimated, to calculate high-energy EM and neutrino signatures and estimate their potential detectability with current and future detectors.