TY - JOUR
T1 - Long-term GRMHD simulations of neutron star merger accretion discs
T2 - Implications for electromagnetic counterparts
AU - Fernández, Rodrigo
AU - Tchekhovskoy, Alexander
AU - Quataert, Eliot
AU - Foucart, Francois
AU - Kasen, Daniel
N1 - Funding Information:
We thank Meng-Ru Wu, Yong-Zhong Qian, and Stéphane Goriely for helpful discussions. We also thank Daniel Siegel for providing additional information about published simulation results, and Austin Harris for help with running simulations. The anonymous referee provided constructive comments that improved the presentation of the paper. RF acknowledges support from the Natural Sciences and Engineering Research Council (NSERC) of Canada, and from the Faculty of Science at the University of Alberta. AT acknowledges support from Northwestern University. EQ was supported in part by a Simons Investigator award from the Simons Foundation, and the David and Lucile Packard Foundation. This work was also supported in part by the Gordon and Betty Moore Foundation through Grant GBMF5076. Support for this work was provided by NASA through Einstein Postdoctoral Fellowship grant numbers PF4-150122 (FF) and PF3-140115 (AT) awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060, and through grant 80NSSC18K0565 (FF, AT). DK is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under contract numbers DE-AC02-05CH11231, DESC0017616, and DE-SC0018297. The software used in this work was in part developed by the DOE NNSA-ASC OASCR Flash Center at the University of Chicago. This research used resources of the National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Computations were performed at Carver and Edison (repositories m1186, m2058, m2401, and the scavenger queue).
Funding Information:
We thank Meng-Ru Wu, Yong-Zhong Qian, and Stéphane Goriely for helpful discussions. We also thank Daniel Siegel for providing additional information about published simulation results, and Austin Harris for help with running simulations. The anonymous referee provided constructive comments that improved the presentation of the paper. RF acknowledges support from the Natural Sciences and Engineering Research Council (NSERC) of Canada, and from the Faculty of Science at the University of Alberta. AT acknowledges support from Northwestern University. EQ was supported in part by a Simons Investigator award from the Simons Foundation, and the David and Lucile Packard Foundation. This work was also supported in part by the Gordon and Betty Moore Foundation through Grant GBMF5076. Support for this work was provided by NASA through Einstein Postdoctoral Fellowship grant numbers PF4-150122 (FF) and PF3-140115 (AT) awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060, and through grant 80NSSC18K0565 (FF, AT). DK is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under contract numbers DE-AC02-05CH11231, DE-SC0017616, and DE-SC0018297. The software used in this work was in part developed by the DOE NNSA-ASC OASCR Flash Center at the University of Chicago. This research used resources of the National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Computations were performed at Carver and Edison (repositories m1186, m2058, m2401, and the scavenger queue).
Publisher Copyright:
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
PY - 2019/1/21
Y1 - 2019/1/21
N2 - We investigate the long-term evolution of black hole accretion discs formed in neutron star mergers. These discs expel matter that contributes to an r-process kilonova, and can produce relativistic jets powering short gamma-ray bursts. Here we report the results of a three-dimensional, general-relativistic magnetohydrodynamic (GRMHD) simulation of such a disc which is evolved for long enough (∼9 s, or ∼6 × 105rg/c) to achieve completion of mass ejection far from the disc. Our model starts with a poloidal field, and fully resolves the most unstable mode of the magnetorotational instability. We parametrize the dominant microphysics and neutrino cooling effects, and compare with axisymmetric hydrodynamic models with shear viscosity. The GRMHD model ejects mass in two ways: a prompt MHD-mediated outflow and a late-time, thermally driven wind once the disc becomes advective. The total amount of unbound mass ejected (0.013 M, or 40 per cent of the initial torus mass) is twice as much as in hydrodynamic models, with higher average velocity (0.1c) and a broad electron fraction distribution with a lower average value (0.16). Scaling the ejected fractions to a disc mass of ∼0.1 M can account for the red kilonova from GW170817 but underpredicts the blue component. About ∼10−3 M of material should undergo neutron freezout and could produce a bright kilonova precursor in the first few hours after the merger. With our idealized initial magnetic field configuration, we obtain a robust jet and sufficient ejecta with Lorentz factor ∼1−10 to (over)produce the non-thermal emission from GW1708107.
AB - We investigate the long-term evolution of black hole accretion discs formed in neutron star mergers. These discs expel matter that contributes to an r-process kilonova, and can produce relativistic jets powering short gamma-ray bursts. Here we report the results of a three-dimensional, general-relativistic magnetohydrodynamic (GRMHD) simulation of such a disc which is evolved for long enough (∼9 s, or ∼6 × 105rg/c) to achieve completion of mass ejection far from the disc. Our model starts with a poloidal field, and fully resolves the most unstable mode of the magnetorotational instability. We parametrize the dominant microphysics and neutrino cooling effects, and compare with axisymmetric hydrodynamic models with shear viscosity. The GRMHD model ejects mass in two ways: a prompt MHD-mediated outflow and a late-time, thermally driven wind once the disc becomes advective. The total amount of unbound mass ejected (0.013 M, or 40 per cent of the initial torus mass) is twice as much as in hydrodynamic models, with higher average velocity (0.1c) and a broad electron fraction distribution with a lower average value (0.16). Scaling the ejected fractions to a disc mass of ∼0.1 M can account for the red kilonova from GW170817 but underpredicts the blue component. About ∼10−3 M of material should undergo neutron freezout and could produce a bright kilonova precursor in the first few hours after the merger. With our idealized initial magnetic field configuration, we obtain a robust jet and sufficient ejecta with Lorentz factor ∼1−10 to (over)produce the non-thermal emission from GW1708107.
KW - Accretion, accretion discs
KW - Gravitation
KW - MHD
KW - Neutrinos
KW - Nuclear reactions, nucleosynthesis, abundances
UR - http://www.scopus.com/inward/record.url?scp=85057265242&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85057265242&partnerID=8YFLogxK
U2 - 10.1093/mnras/sty2932
DO - 10.1093/mnras/sty2932
M3 - Article
AN - SCOPUS:85057265242
SN - 0035-8711
VL - 482
SP - 3373
EP - 3393
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 3
ER -