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Title: Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers

Abstract

We investigate the nucleosynthesis of heavy elements in the winds ejected by accretion discs formed in neutron star mergers. We compute the element formation in disc outflows from hypermassive neutron star (HMNS) remnants of variable lifetime, including the effect of angular momentum transport in the disc evolution. We employ long-term axisymmetric hydrodynamic disc simulations to model the ejecta, and compute r-process nucleosynthesis with tracer particles using a nuclear reaction network containing ~8000 species. We find that the previously known strong correlation between HMNS lifetime, ejected mass and average electron fraction in the outflow is directly related to the amount of neutrino irradiation on the disc, which dominates mass ejection at early times in the form of a neutrino-driven wind. Production of lanthanides and actinides saturates at short HMNS lifetimes (≲10 ms), with additional ejecta contributing to a blue optical kilonova component for longer-lived HMNSs. We find good agreement between the abundances from the disc outflow alone and the solar r-process distribution only for short HMNS lifetimes (≲10 ms). For longer lifetimes, the rare-earth and third r-process peaks are significantly underproduced compared to the solar pattern, requiring additional contributions from the dynamical ejecta. The nucleosynthesis signature from a spinning black holemore » (BH) can only overlap with that from an HMNS of moderate lifetime (≲60 ms). Finally, we show that angular momentum transport not only contributes with a late-time outflow component, but that it also enhances the neutrino-driven component by moving material to shallower regions of the gravitational potential, in addition to providing additional heating.« less

Authors:
 [1];  [2];  [3];  [4];  [5];  [4];  [6]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  2. Univ. of Alberta, Edmonton, AB (Canada); Univ. of California, Berkeley, CA (United States)
  3. Michigan State Univ., East Lansing, MI (United States)
  4. Columbia Univ., New York, NY (United States). Columbia Astrophysics Lab.
  5. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  6. California Inst. of Technology (CalTech), Pasadena, CA (United States); Kyoto Univ. (Japan)
Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Sponsoring Org.:
USDOE
OSTI Identifier:
1526485
Resource Type:
Accepted Manuscript
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Volume: 472; Journal Issue: 1; Journal ID: ISSN 0035-8711
Publisher:
Royal Astronomical Society
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS

Citation Formats

Lippuner, Jonas, Fernández, Rodrigo, Roberts, Luke F., Foucart, Francois, Kasen, Daniel, Metzger, Brian D., and Ott, Christian D. Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers. United States: N. p., 2017. Web. doi:10.1093/mnras/stx1987.
Lippuner, Jonas, Fernández, Rodrigo, Roberts, Luke F., Foucart, Francois, Kasen, Daniel, Metzger, Brian D., & Ott, Christian D. Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers. United States. doi:10.1093/mnras/stx1987.
Lippuner, Jonas, Fernández, Rodrigo, Roberts, Luke F., Foucart, Francois, Kasen, Daniel, Metzger, Brian D., and Ott, Christian D. Wed . "Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers". United States. doi:10.1093/mnras/stx1987. https://www.osti.gov/servlets/purl/1526485.
@article{osti_1526485,
title = {Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers},
author = {Lippuner, Jonas and Fernández, Rodrigo and Roberts, Luke F. and Foucart, Francois and Kasen, Daniel and Metzger, Brian D. and Ott, Christian D.},
abstractNote = {We investigate the nucleosynthesis of heavy elements in the winds ejected by accretion discs formed in neutron star mergers. We compute the element formation in disc outflows from hypermassive neutron star (HMNS) remnants of variable lifetime, including the effect of angular momentum transport in the disc evolution. We employ long-term axisymmetric hydrodynamic disc simulations to model the ejecta, and compute r-process nucleosynthesis with tracer particles using a nuclear reaction network containing ~8000 species. We find that the previously known strong correlation between HMNS lifetime, ejected mass and average electron fraction in the outflow is directly related to the amount of neutrino irradiation on the disc, which dominates mass ejection at early times in the form of a neutrino-driven wind. Production of lanthanides and actinides saturates at short HMNS lifetimes (≲10 ms), with additional ejecta contributing to a blue optical kilonova component for longer-lived HMNSs. We find good agreement between the abundances from the disc outflow alone and the solar r-process distribution only for short HMNS lifetimes (≲10 ms). For longer lifetimes, the rare-earth and third r-process peaks are significantly underproduced compared to the solar pattern, requiring additional contributions from the dynamical ejecta. The nucleosynthesis signature from a spinning black hole (BH) can only overlap with that from an HMNS of moderate lifetime (≲60 ms). Finally, we show that angular momentum transport not only contributes with a late-time outflow component, but that it also enhances the neutrino-driven component by moving material to shallower regions of the gravitational potential, in addition to providing additional heating.},
doi = {10.1093/mnras/stx1987},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 1,
volume = 472,
place = {United States},
year = {2017},
month = {8}
}

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