paper

Effects of spin on magnetized binary neutron star mergers and jet launching

arXiv:1902.08636 · doi:10.1103/PhysRevD.99.084032

Abstract

Events GW170817 and GRB 170817A provide the best confirmation so far that compact binary mergers where at least one of the companions is a neutron star (NS) can be the progenitors of short gamma-ray bursts (sGRBs). An open question for GW170817 remains the values and impact of the initial NS spins. The initial spins could possibly affect the remnant black hole (BH) mass and spin, the remnant disk and the formation and lifetime of a jet and its luminosity. Here we summarize our general relativistic magnetohydrodynamic simulations of spinning, NS binaries undergoing merger and delayed collapse to a BH. The binaries consist of two identical NSs, modeled as polytropes, in quasicircular orbit, each with spins , or . The stars are endowed initially with a dipolar magnetic field extending from the interior into the exterior, as in a radio pulsar. Following merger, the redistribution of angular momentum by magnetic braking and magnetic turbulent viscosity in the hypermassive neutron star (HMNS) remnant, along with the loss of angular momentum due to gravitational radiation, induce the formation of a massive, nearly uniformly rotating inner core surrounded by a magnetized Keplerian disk-like envelope. The HMNS eventually collapses to a BH, with spin independent of the initial spin of the NSs, surrounded by a magnetized accretion disk. The larger the initial NS spin the heavier the disk. After following merger, a mildly relativistic jet is launched. The lifetime of the jet [] and its outgoing Poynting luminosity [] are consistent with typical sGRBs, as well as with the Blandford--Znajek mechanism for launching jets and their associated Poynting luminosities.

arXiv comment16 pages, 11 figures. Matches published version. Simulations are available at http://research.physics.illinois.edu/cta/movies/NSNS_2018/

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