The impact of disk outflows on the structure of short GRB jets at large scales

Abstract: Short Gamma-Ray Bursts (GRBs) are known to be associated with binary neutron star (NSNS) or black hole-neutron star (BHNS) mergers. The detection of gravitational wave and its associated electromagnetic counterparts GW/GRB 170817A has shown that interactions between relativistic jets and mildly relativistic ejecta influence observed radiation. Previous studies simulated a uniform jet propagating through a homologously expanding wind, however, jets and disk outflows are launched together during accretion, making the interaction more complex. We investigate how the disk wind impacts jet propagation at distances $r\sim 10^8\,-\,10^{11}~$cm. We are using two-dimensional special relativistic hydrodynamical simulations. As initial conditions, we remap the outflows from general relativistic magnetohydrodynamical simulations of BH accretion disks that represent post-merger NSNS or BHNS remnants. We account for wind stratification and r-process nucleosynthesis, which alter the pressure profile from that of an ideal gas in the initial conditions. We found that a) self-consistent wind pressure leads to significant changes in the jet collimation and cocoon expansion; b) the angular structure of thermal and kinetic energy components in the jets, cocoons, and winds differ with respect to simple homologous models; c) the temporal evolution of the structure reveals conversion of thermal to kinetic energy being different for each component in the system (jet, cocoon, and wind); d) dynamical ejecta alters the interaction between jets and disk winds. Our results show that the jet and cocoon structure is shaped by the accretion disk wind that alters the effect of dynamical ejecta and may have an impact on the observed afterglow emission.