Inferring properties of binary neutron star mergers from the shock breakout emission*

Neutron star (NS) mergers are amongst the most promising multimessenger sources in the Universe, as demonstrated by the coincident detection of gravitational waves (GWs) with multi-wavelength electromagnetic (EM) radiation for GW170817. Short gamma-ray bursts (GRBs) are thought to originate from relativistic jets launched by NS merger remnants. However, there are still uncertainties about the exact nature of such a remnant: whether it is a promptly formed black hole (BH), a hypermassive NS that later collapses to a BH or a stable NS. The engine properties, in particular the jet launching mechanism, can affect the jet evolution and their observable signatures. In this work, we investigate the propagation of jets through realistic NS merger ejecta modeled through General-Relativistic Hydrodynamic (GRHD) simulations. We construct a semi-analytical jet+cocoon propagation model and examine the conditions under which these successfully break out from the ejecta. We calculate the EM emission associated with the shock breakout and compare several NS merger simulations with different microphysics or binary configurations with the gamma-ray observational data from GW170817. With this analysis, we infer the most favorable engine properties and nuclear microphysics for this event.