Long-term GRMHD simulations of neutron star merger accretion discs: implications for electromagnetic counterparts

• DOI: 10.1093/mnras/sty2932
• Publication Date: 2018-10-29T17:00:34Z
• Authors: Rodrigo Fernández; Alexander Tchekho...; Eliot Quataert; Francois Foucart; Daniel Kasen
• Keywords: Kilonova; Magnetorotational instability; Black hole (networking)

We investigate the long-term evolution of black hole accretion disks formed in neutron star mergers. These expel matter that contributes to an $r$-process kilonova, and can produce relativistic jets powering short gamma-ray bursts. Here we report results a three-dimensional, general-relativistic magnetohydrodynamic (GRMHD) simulation such disk which is evolved for long enough ($\sim 9$s, or $\sim 6\times 10^5 r_{\rm g}/c$) achieve completion mass ejection far from disk. Our model starts with poloidal field, fully resolves most unstable mode magnetorotational instability. parameterize dominant microphysics neutrino cooling effects, compare axisymmetric hydrodynamic models shear viscosity. The GRMHD ejects two ways: prompt MHD-mediated outflow late-time, thermally-driven wind once becomes advective. total amount unbound ejected ($0.013M_\odot$, $\simeq 40\%$ initial torus mass) twice as much models, higher average velocity ($0.1c$) broad electron fraction distribution lower value ($0.16$). Scaling fractions 0.1M_\odot$ account red kilonova GW170817 but underpredicts blue component. About 10^{-3}M_\odot$ material should undergo freezout could bright precursor first few hours after merger. With our idealized magnetic field configuration, obtain robust jet sufficient ejecta Lorentz factor 1-10$ (over)produce non-thermal emission GW1708107.