TY - JOUR
T1 - Outflows from accretion discs formed in neutron star mergers
T2 - Effect of black hole spin
AU - Fernández, Rodrigo
AU - Kasen, Daniel
AU - Metzger, Brian D.
AU - Quataert, Eliot
N1 - Publisher Copyright:
© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
Copyright:
Copyright 2016 Elsevier B.V., All rights reserved.
PY - 2015/1/1
Y1 - 2015/1/1
N2 - The accretion disc that forms after a neutron star merger is a source of neutron-rich ejecta. The ejected material contributes to a radioactively powered electromagnetic transient, with properties that depend sensitively on the composition of the outflow. Here, we investigate how the spin of the black hole (BH) remnant influences mass ejection on the thermal and viscous time-scales. We carry out two-dimensional, time-dependent hydrodynamic simulations of merger remnant accretion discs including viscous angular momentum transport and approximate neutrino self-irradiation. The gravity of the spinning BH is included via a pseudo-Newtonian potential. We find that a disc around a spinning BH ejects more mass, up to a factor of several, relative to the non-spinning case. The enhanced mass-loss is due to energy release by accretion occurring deeper in the gravitational potential, raising the disc temperature and hence the rate of viscous heating in regions where neutrino cooling is ineffective. The mean electron fraction of the outflow increases moderately with BH spin due to a highly irradiated (though not neutrino-driven) wind component. While the bulk of the ejecta is still very neutron-rich, thus generating heavy r-process elements, the leading edge of the wind contains a small amount of Lanthanide-free material. This component can give rise to an ≲1 d blue optical 'bump' in a kilonova light curve, even in the case of prompt BH formation, which may facilitate its detection.
AB - The accretion disc that forms after a neutron star merger is a source of neutron-rich ejecta. The ejected material contributes to a radioactively powered electromagnetic transient, with properties that depend sensitively on the composition of the outflow. Here, we investigate how the spin of the black hole (BH) remnant influences mass ejection on the thermal and viscous time-scales. We carry out two-dimensional, time-dependent hydrodynamic simulations of merger remnant accretion discs including viscous angular momentum transport and approximate neutrino self-irradiation. The gravity of the spinning BH is included via a pseudo-Newtonian potential. We find that a disc around a spinning BH ejects more mass, up to a factor of several, relative to the non-spinning case. The enhanced mass-loss is due to energy release by accretion occurring deeper in the gravitational potential, raising the disc temperature and hence the rate of viscous heating in regions where neutrino cooling is ineffective. The mean electron fraction of the outflow increases moderately with BH spin due to a highly irradiated (though not neutrino-driven) wind component. While the bulk of the ejecta is still very neutron-rich, thus generating heavy r-process elements, the leading edge of the wind contains a small amount of Lanthanide-free material. This component can give rise to an ≲1 d blue optical 'bump' in a kilonova light curve, even in the case of prompt BH formation, which may facilitate its detection.
KW - Accretion, accretion discs
KW - Dense matter
KW - Gravitational waves
KW - Hydrodynamics
KW - Neutrinos
KW - Nuclear reactions, nucleosynthesis, abundances
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U2 - 10.1093/mnras/stu2112
DO - 10.1093/mnras/stu2112
M3 - Article
AN - SCOPUS:84924517150
VL - 446
SP - 750
EP - 758
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 1
ER -