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

Fernández, Rodrigo and Foucart, Francois and Kasen, Daniel and Lippuner, Jonas and Desai, Dhruv and Roberts, Luke F. (2017) Dynamics, nucleosynthesis, and kilonova signature of black hole—neutron star merger ejecta. Classical and Quantum Gravity, 34 (15). Art. No. 154001. ISSN 0264-9381.

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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 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lippuner, Jonas0000-0002-5936-3485
Roberts, Luke F.0000-0001-7364-7946
Additional Information:© 2017 IOP Publishing Ltd. Received 9 December 2016, revised 2 June 2017; Accepted for publication 20 June 2017; Published 4 July 2017. We thank Kenta Hotokezaka, Masaomi Tanaka, Kunihito Ioka, and Shinya Wanajo for useful discussions. We also thank the anonymous referee for helpful comments that improved the presentation of this paper. RF acknowledges support from the University of California Office of the President, from NSF grant AST-1206097, and from the Faculty of Science at the University of Alberta. Support for this work was provided by NASA through Einstein Postdoctoral Fellowship grant numbered PF4-150122 (FF) awarded by the Chandra x-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. DK is supported in part by a Department of Energy Office of Nuclear Physics Early Career Award, and by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Divisions of Nuclear Physics, of the US Department of Energy under Contract No. DE-AC02-05CH11231. 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 Edison (repositories m1186 and m2058). This research also used the Savio computational cluster resource provided by the Berkeley Research Computing program at the University of California, Berkeley (supported by the UC Berkeley Chancellor, Vice Chancellor of Research, and Office of the CIO). We also thank the hospitality of the Yukawa Institute for Theoretical Physics through the workshop Nuclear Physics, Compact Stars, and Compact Star Mergers 2016, during which part of this work was carried out.
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
University of CaliforniaUNSPECIFIED
University of AlbertaUNSPECIFIED
NASA Einstein FellowshipPF4-150122
Department of Energy (DOE)DE-AC02-05CH11231
Subject Keywords:accretion, accretion disks, dense matter, gravitational waves, hydrodynamics, neutrinos, nuclear reactions, nucleosynthesis, abundances
Record Number:CaltechAUTHORS:20170727-083604924
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Official Citation:Rodrigo Fernández et al 2017 Class. Quantum Grav. 34 154001
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79477
Deposited By: Tony Diaz
Deposited On:27 Jul 2017 15:51
Last Modified:27 Jul 2017 15:51

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