Effects of spin on magnetized binary neutron star mergers and jet launching. (arXiv:1902.08636v1 [astro-ph.HE])

Effects of spin on magnetized binary neutron star mergers and jet launching. (arXiv:1902.08636v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ruiz_M/0/1/0/all/0/1">Milton Ruiz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tsokaros_A/0/1/0/all/0/1">Antonios Tsokaros</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Paschalidis_V/0/1/0/all/0/1">Vasileios Paschalidis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shapiro_S/0/1/0/all/0/1">Stuart L. Shapiro</a>

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 impact of the initial NS spins, which can strongly
affect the remnant black hole (BH) mass and spin, the remnant disk and the
formation and lifetime of a jet and its outgoing Poynting 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 $Gamma=2$ polytropes, in
quasicircular orbit, each with spins $chi_{rm{NS}}=-0.053,,0,,0.24$, 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 BH,
with spin $a/M_{rm BH} simeq 0.78$ 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 $Delta tsim 3000-4000 M sim 45-60(M_{rm
NS}/1.625M_odot)rm ms$ following merger, a mildly relativistic jet is
launched. The lifetime of the jet [$Delta tsim 100-140(M_{rm
NS}/1.625M_odot)rm ms$] and its outgoing Poynting luminosity [$L_{rm EM}sim
10^{51.5pm 1}rm erg/s$] are consistent with typical sGRBs, as well as with
the Blandford–Znajek mechanism for launching jets and their associated
Poynting luminosities.

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 impact of the initial NS spins, which can strongly
affect the remnant black hole (BH) mass and spin, the remnant disk and the
formation and lifetime of a jet and its outgoing Poynting 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 $Gamma=2$ polytropes, in
quasicircular orbit, each with spins $chi_{rm{NS}}=-0.053,,0,,0.24$, 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 BH,
with spin $a/M_{rm BH} simeq 0.78$ 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 $Delta tsim 3000-4000 M sim 45-60(M_{rm
NS}/1.625M_odot)rm ms$ following merger, a mildly relativistic jet is
launched. The lifetime of the jet [$Delta tsim 100-140(M_{rm
NS}/1.625M_odot)rm ms$] and its outgoing Poynting luminosity [$L_{rm EM}sim
10^{51.5pm 1}rm erg/s$] are consistent with typical sGRBs, as well as with
the Blandford–Znajek mechanism for launching jets and their associated
Poynting luminosities.

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