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 can be the progenitors of short gamma-ray bursts ( sGRBs ) .
An open question for GW170817 remains the values and impact of the initial neutron star spins .
The initial spins could possibly affect the remnant black hole mass and spin , the remnant disk and the formation and lifetime of a jet and its outgoing electromagnetic Poynting luminosity .
Here we summarize our general relativistic magnetohydrodynamic simulations of spinning , neutron star binaries undergoing merger and delayed collapse to a black hole .
The binaries consist of two identical stars , modeled as \Gamma = 2 polytropes , in quasicircular orbit , each with spins \chi _ { NS } = -0.053 , 0 , 0.24 , or 0.36 .
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 black hole , with spin a / M _ { BH } \simeq 0.78 independent of the initial spin of the neutron stars , surrounded by a magnetized accretion disk .
The larger the initial neutron star spin the heavier the disk .
After \Delta t \sim 3000 M - 4000 M \sim 45 ( M _ { NS } / 1.625 M _ { \odot } ) ms - 60 ( M _ { NS } % / 1.625 M _ { \odot } ) ms following merger , a mildly relativistic jet is launched .
The lifetime of the jet [ \Delta t \sim 100 ( M _ { NS } / 1.625 M _ { \odot } ) { ms } -140 ( M _ { NS } / 1.625 M _ { % \odot } ) ms ] and its outgoing Poynting luminosity [ L _ { EM } \sim 10 ^ { 51.5 \pm 1 } erg / s ] are consistent with typical sGRBs , as well as with the Blandford–Znajek mechanism for launching jets and their associated Poynting luminosities .