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Title: The role of magnetic field geometry in the evolution of neutron star merger accretion discs

Abstract

ABSTRACT Neutron star mergers are unique laboratories of accretion, ejection, and r-process nucleosynthesis. We used 3D general relativistic magnetohydrodynamic simulations to study the role of the post-merger magnetic geometry in the evolution of merger remnant discs around stationary Kerr black holes. Our simulations fully capture mass accretion, ejection, and jet production, owing to their exceptionally long duration exceeding 4 s. Poloidal post-merger magnetic field configurations produce jets with energies Ejet ∼ (4–30) × 1050 erg, isotropic equivalent energies Eiso ∼ (4–20) × 1052 erg, opening angles θjet ∼ 6–13°, and durations tj ≲ 1 s. Accompanying the production of jets is the ejection of $$f_\mathrm{ej}\sim 30\!-\!40{{\ \rm per\ cent}}$$ of the post-merger disc mass, continuing out to times >1 s. We discover that a more natural, purely toroidal post-merger magnetic field geometry generates large-scale poloidal magnetic flux of alternating polarity and striped jets. The first stripe, of $$E_\mathrm{jet}\simeq 2\times 10^{48}\, \mathrm{erg}$$, Eiso ∼ 1051 erg, θjet ∼ 3.5–5°, and tj ∼ 0.1 s, is followed by ≳4 s of striped jet activity with $$f_\mathrm{ej}\simeq 27{{\ \rm per\ cent}}$$. The dissipation of such stripes could power the short-duration gamma-ray burst (sGRB) prompt emission. Our simulated jet energies and durations span the range of sGRBs. We find that although the blue kilonova component is initially hidden from view by the red component, it expands faster, outruns the red component, and becomes visible to off-axis observers. In comparison to GW 170817/GRB 170817A, our simulations underpredict the mass of the blue relative to red component by a factor of few. Including the dynamical ejecta and neutrino absorption may reduce this tension.

Authors:
 [1];  [1];  [1]; ORCiD logo [2];  [3]; ORCiD logo [4];  [5]
  1. Center for Interdisciplinary Exploration & Research in Astrophysics (CIERA), Physics & Astronomy, Northwestern University, Evanston, IL 60202, USA
  2. Department of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada
  3. Department of Physics and Astronomy, University of New Hampshire, Durham, NH 03824, USA
  4. Departments of Physics & Astronomy, and Theoretical Astrophysics Center, University of California, Berkeley, CA 94720, USA
  5. Departments of Physics & Astronomy, and Theoretical Astrophysics Center, University of California, Berkeley, CA 94720, USA, Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1574033
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Published Article
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Name: Monthly Notices of the Royal Astronomical Society Journal Volume: 490 Journal Issue: 4; Journal ID: ISSN 0035-8711
Publisher:
Oxford University Press
Country of Publication:
United Kingdom
Language:
English

Citation Formats

Christie, I. M., Lalakos, A., Tchekhovskoy, A., Fernández, R., Foucart, F., Quataert, E., and Kasen, D. The role of magnetic field geometry in the evolution of neutron star merger accretion discs. United Kingdom: N. p., 2019. Web. doi:10.1093/mnras/stz2552.
Christie, I. M., Lalakos, A., Tchekhovskoy, A., Fernández, R., Foucart, F., Quataert, E., & Kasen, D. The role of magnetic field geometry in the evolution of neutron star merger accretion discs. United Kingdom. doi:10.1093/mnras/stz2552.
Christie, I. M., Lalakos, A., Tchekhovskoy, A., Fernández, R., Foucart, F., Quataert, E., and Kasen, D. Mon . "The role of magnetic field geometry in the evolution of neutron star merger accretion discs". United Kingdom. doi:10.1093/mnras/stz2552.
@article{osti_1574033,
title = {The role of magnetic field geometry in the evolution of neutron star merger accretion discs},
author = {Christie, I. M. and Lalakos, A. and Tchekhovskoy, A. and Fernández, R. and Foucart, F. and Quataert, E. and Kasen, D.},
abstractNote = {ABSTRACT Neutron star mergers are unique laboratories of accretion, ejection, and r-process nucleosynthesis. We used 3D general relativistic magnetohydrodynamic simulations to study the role of the post-merger magnetic geometry in the evolution of merger remnant discs around stationary Kerr black holes. Our simulations fully capture mass accretion, ejection, and jet production, owing to their exceptionally long duration exceeding 4 s. Poloidal post-merger magnetic field configurations produce jets with energies Ejet ∼ (4–30) × 1050 erg, isotropic equivalent energies Eiso ∼ (4–20) × 1052 erg, opening angles θjet ∼ 6–13°, and durations tj ≲ 1 s. Accompanying the production of jets is the ejection of $f_\mathrm{ej}\sim 30\!-\!40{{\ \rm per\ cent}}$ of the post-merger disc mass, continuing out to times >1 s. We discover that a more natural, purely toroidal post-merger magnetic field geometry generates large-scale poloidal magnetic flux of alternating polarity and striped jets. The first stripe, of $E_\mathrm{jet}\simeq 2\times 10^{48}\, \mathrm{erg}$, Eiso ∼ 1051 erg, θjet ∼ 3.5–5°, and tj ∼ 0.1 s, is followed by ≳4 s of striped jet activity with $f_\mathrm{ej}\simeq 27{{\ \rm per\ cent}}$. The dissipation of such stripes could power the short-duration gamma-ray burst (sGRB) prompt emission. Our simulated jet energies and durations span the range of sGRBs. We find that although the blue kilonova component is initially hidden from view by the red component, it expands faster, outruns the red component, and becomes visible to off-axis observers. In comparison to GW 170817/GRB 170817A, our simulations underpredict the mass of the blue relative to red component by a factor of few. Including the dynamical ejecta and neutrino absorption may reduce this tension.},
doi = {10.1093/mnras/stz2552},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 4,
volume = 490,
place = {United Kingdom},
year = {2019},
month = {9}
}

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