Multi-messenger signals from short gamma ray bursts

Abstract

We present the results of simulations done with the code HARM-COOL developed in the CTP PAS Warsaw research group over the years 2017-2019. It is based in the original GR MHD scheme proposed by Gammie et al. (2003) for the simulation of Active Galactic Nucleus, but now it has been suited for the engine of a short Gamma Ray Burst event. We compute time-dependent evolution of a black hole accretion disk, in two-dimensional, axisymmetric scheme. The code includes neutrino cooling and accounts for nuclear structure of dense, degenerate matter. Free protons, neutrons, and electron-positron pairs form a neutron-rich, magnetically driven outflow that provides site for subsequent r-process nucleosynthesis. Here the heavy elements up to the Uranium and Gold are synthesized and may contribute to the chemical enrichment of the circum-burst medium. Their radio-active decay will give signal in lower energies in a timescale of weeks-months after the GRB prompt phase. In addition, the magnetic fields are responsible for the launching of ultra-relativistic jets along the rotation axis of the central black hole, according to the well-known Blandford-Znajek mechanism. These jets are sites of variable high energy emission in gamma rays. We find that the magnetic field and the black hole spin account for the observed variability timescales and jet energetics.