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Title: A line-binned treatment of opacities for the spectra and light curves from neutron star mergers

Abstract

ABSTRACT The electromagnetic observations of GW170817 were able to dramatically increase our understanding of neutron star mergers beyond what we learned from gravitational waves alone. These observations provided insight on all aspects of the merger from the nature of the gamma-ray burst to the characteristics of the ejected material. The ejecta of neutron star mergers are expected to produce such electromagnetic transients, called kilonovae or macronovae. Characteristics of the ejecta include large velocity gradients, relative to supernovae, and the presence of heavy r-process elements, which pose significant challenges to the accurate calculation of radiative opacities and radiation transport. For example, these opacities include a dense forest of bound–bound features arising from near-neutral lanthanide and actinide elements. Here we investigate the use of fine-structure, line-binned opacities that preserve the integral of the opacity over frequency. Advantages of this area-preserving approach over the traditional expansion–opacity formalism include the ability to pre-calculate opacity tables that are independent of the type of hydrodynamic expansion and thus eliminate the computational expense of calculating opacities within radiation-transport simulations. Tabular opacities are generated for all 14 lanthanides as well as a representative actinide element, uranium. We demonstrate that spectral simulations produced with the line-binned opacities agree wellmore » with results produced with the more accurate continuous Monte Carlo Sobolev approach, as well as with the commonly used expansion–opacity formalism. The agreement between the line-binned and expansion–opacity results is explained as arising from the similarity in their opacities in the limit of low optical depth, where radiation transport is important in the ejecta. Additional investigations illustrate the convergence of opacity with respect to the number of included lines, and elucidate sensitivities to different atomic physics approximations, such as fully and semirelativistic approaches.« less

Authors:
ORCiD logo [1];  [2];  [1];  [1]; ORCiD logo [1]
  1. Los Alamos National Laboratory, Los Alamos, NM 87545, USA
  2. Los Alamos National Laboratory, Los Alamos, NM 87545, USA, Physics Department, University of Arizona, Tucson, AZ 85721, USA, Physics and Astronomy Department, University of New Mexico, Albuquerque, NM 87131, USA
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1605037
Grant/Contract Number:  
[89233218CNA000001]
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: 493 Journal Issue: 3]; Journal ID: ISSN 0035-8711
Publisher:
Oxford University Press
Country of Publication:
United Kingdom
Language:
English

Citation Formats

Fontes, C. J., Fryer, C. L., Hungerford, A. L., Wollaeger, R. T., and Korobkin, O. A line-binned treatment of opacities for the spectra and light curves from neutron star mergers. United Kingdom: N. p., 2020. Web. doi:10.1093/mnras/staa485.
Fontes, C. J., Fryer, C. L., Hungerford, A. L., Wollaeger, R. T., & Korobkin, O. A line-binned treatment of opacities for the spectra and light curves from neutron star mergers. United Kingdom. doi:10.1093/mnras/staa485.
Fontes, C. J., Fryer, C. L., Hungerford, A. L., Wollaeger, R. T., and Korobkin, O. Wed . "A line-binned treatment of opacities for the spectra and light curves from neutron star mergers". United Kingdom. doi:10.1093/mnras/staa485.
@article{osti_1605037,
title = {A line-binned treatment of opacities for the spectra and light curves from neutron star mergers},
author = {Fontes, C. J. and Fryer, C. L. and Hungerford, A. L. and Wollaeger, R. T. and Korobkin, O.},
abstractNote = {ABSTRACT The electromagnetic observations of GW170817 were able to dramatically increase our understanding of neutron star mergers beyond what we learned from gravitational waves alone. These observations provided insight on all aspects of the merger from the nature of the gamma-ray burst to the characteristics of the ejected material. The ejecta of neutron star mergers are expected to produce such electromagnetic transients, called kilonovae or macronovae. Characteristics of the ejecta include large velocity gradients, relative to supernovae, and the presence of heavy r-process elements, which pose significant challenges to the accurate calculation of radiative opacities and radiation transport. For example, these opacities include a dense forest of bound–bound features arising from near-neutral lanthanide and actinide elements. Here we investigate the use of fine-structure, line-binned opacities that preserve the integral of the opacity over frequency. Advantages of this area-preserving approach over the traditional expansion–opacity formalism include the ability to pre-calculate opacity tables that are independent of the type of hydrodynamic expansion and thus eliminate the computational expense of calculating opacities within radiation-transport simulations. Tabular opacities are generated for all 14 lanthanides as well as a representative actinide element, uranium. We demonstrate that spectral simulations produced with the line-binned opacities agree well with results produced with the more accurate continuous Monte Carlo Sobolev approach, as well as with the commonly used expansion–opacity formalism. The agreement between the line-binned and expansion–opacity results is explained as arising from the similarity in their opacities in the limit of low optical depth, where radiation transport is important in the ejecta. Additional investigations illustrate the convergence of opacity with respect to the number of included lines, and elucidate sensitivities to different atomic physics approximations, such as fully and semirelativistic approaches.},
doi = {10.1093/mnras/staa485},
journal = {Monthly Notices of the Royal Astronomical Society},
number = [3],
volume = [493],
place = {United Kingdom},
year = {2020},
month = {2}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1093/mnras/staa485

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