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Title: Dynamics, nucleosynthesis, and kilonova signature of black hole—neutron star merger ejecta

Abstract

We investigate the ejecta from black hole—neutron star mergers by modeling the formation and interaction of mass ejected in a tidal tail and a disk wind. The outflows are neutron-rich, giving rise to optical/infrared emission powered by the radioactive decay of r-process elements (a kilonova). Here we perform an end-to-end study of this phenomenon, where we start from the output of a fully-relativistic merger simulation, calculate the post-merger hydrodynamical evolution of the ejecta and disk winds including neutrino physics, determine the final nucleosynthetic yields using post-processing nuclear reaction network calculations, and compute the kilonova emission with a radiative transfer code. We study the effects of the tail-to-disk mass ratio by scaling the tail density. A larger initial tail mass results in fallback matter becoming mixed into the disk and ejected in the subsequent disk wind. Relative to the case of a disk without dynamical ejecta, the combined outflow has lower mean electron fraction, faster speed, larger total mass, and larger absolute mass free of high-opacity Lanthanides or Actinides. In most cases, the nucleosynthetic yield is dominated by the heavy r-process contribution from the unbound part of the dynamical ejecta. A Solar-like abundance distribution can however be obtained when the total mass of the dynamical ejecta is comparable to the mass of the disk outflows. The kilonova has a characteristic duration of 1 week and a luminosity of ~$$ 10^{41}$$ erg $${\rm s}^{-1}$$ , with orientation effects leading to variations of a factor ~2 in brightness. At early times ($<$ 1 d) the emission includes an optical component from the (hot) Lanthanide-rich material, but the spectrum evolves quickly to the infrared thereafter.

Authors:
 [1];  [2];  [3];  [4];  [5];  [6]
  1. Univ. of Alberta, Edmonton, AB (Canada). Department of Physics; Univ. of California, Berkeley, CA (United States). Dept. of Physics; Univ. of California, Berkeley, CA (United States). Dept. of Astronomy and Theoretical Astrophysics Center
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Nuclear Science Division; NASA Einstein Fellow
  3. Univ. of California, Berkeley, CA (United States). Dept. of Physics; Univ. of California, Berkeley, CA (United States). Dept. of Astronomy and Theoretical Astrophysics Center; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Nuclear Science Division
  4. California Inst. of Technology (CalTech), Pasadena, CA (United States). TAPRI, Walter Burke Institute for Theoretical Physics
  5. Univ. of California, Berkeley, CA (United States). Dept. of Physics
  6. Michigan State Univ., East Lansing, MI (United States). National Superconducting Cyclotron Lab. and Dept. of Physics and Astronomy
Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory-National Energy Research Scientific Computing Center
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE); USDOE Office of Science (SC)
OSTI Identifier:
1523373
DOE Contract Number:  
AC02-05CH11231
Resource Type:
Journal Article
Journal Name:
Classical and Quantum Gravity
Additional Journal Information:
Journal Volume: 34; Journal Issue: 15; Journal ID: ISSN 0264-9381
Publisher:
IOP Publishing
Country of Publication:
United States
Language:
English

Citation Formats

Fernández, Rodrigo, Foucart, Francois, Kasen, Daniel, Lippuner, Jonas, Desai, Dhruv, and Roberts, Luke F. Dynamics, nucleosynthesis, and kilonova signature of black hole—neutron star merger ejecta. United States: N. p., 2017. Web. doi:10.1088/1361-6382/aa7a77.
Fernández, Rodrigo, Foucart, Francois, Kasen, Daniel, Lippuner, Jonas, Desai, Dhruv, & Roberts, Luke F. Dynamics, nucleosynthesis, and kilonova signature of black hole—neutron star merger ejecta. United States. doi:10.1088/1361-6382/aa7a77.
Fernández, Rodrigo, Foucart, Francois, Kasen, Daniel, Lippuner, Jonas, Desai, Dhruv, and Roberts, Luke F. Wed . "Dynamics, nucleosynthesis, and kilonova signature of black hole—neutron star merger ejecta". United States. doi:10.1088/1361-6382/aa7a77.
@article{osti_1523373,
title = {Dynamics, nucleosynthesis, and kilonova signature of black hole—neutron star merger ejecta},
author = {Fernández, Rodrigo and Foucart, Francois and Kasen, Daniel and Lippuner, Jonas and Desai, Dhruv and Roberts, Luke F.},
abstractNote = {We investigate the ejecta from black hole—neutron star mergers by modeling the formation and interaction of mass ejected in a tidal tail and a disk wind. The outflows are neutron-rich, giving rise to optical/infrared emission powered by the radioactive decay of r-process elements (a kilonova). Here we perform an end-to-end study of this phenomenon, where we start from the output of a fully-relativistic merger simulation, calculate the post-merger hydrodynamical evolution of the ejecta and disk winds including neutrino physics, determine the final nucleosynthetic yields using post-processing nuclear reaction network calculations, and compute the kilonova emission with a radiative transfer code. We study the effects of the tail-to-disk mass ratio by scaling the tail density. A larger initial tail mass results in fallback matter becoming mixed into the disk and ejected in the subsequent disk wind. Relative to the case of a disk without dynamical ejecta, the combined outflow has lower mean electron fraction, faster speed, larger total mass, and larger absolute mass free of high-opacity Lanthanides or Actinides. In most cases, the nucleosynthetic yield is dominated by the heavy r-process contribution from the unbound part of the dynamical ejecta. A Solar-like abundance distribution can however be obtained when the total mass of the dynamical ejecta is comparable to the mass of the disk outflows. The kilonova has a characteristic duration of 1 week and a luminosity of ~$ 10^{41}$ erg ${\rm s}^{-1}$ , with orientation effects leading to variations of a factor ~2 in brightness. At early times ($<$ 1 d) the emission includes an optical component from the (hot) Lanthanide-rich material, but the spectrum evolves quickly to the infrared thereafter.},
doi = {10.1088/1361-6382/aa7a77},
journal = {Classical and Quantum Gravity},
issn = {0264-9381},
number = 15,
volume = 34,
place = {United States},
year = {2017},
month = {7}
}

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