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Lanthanides or Dust in Kilonovae: Lessons Learned from GW170817

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journal contribution
posted on 09.04.2018, 08:48 by Christa Gall, Jens Hjorth, Stephan Rosswog, Nial R. Tanvir, Andrew J. Levan
The unprecedented optical and near-infrared lightcurves of the first electromagnetic counterpart to a gravitational-wave source, GW170817, a binary neutron star merger, exhibited a strong evolution from blue to near-infrared (a so-called "kilonova" or "macronova"). The emerging near-infrared component is widely attributed to the formation of r-process elements that provide the opacity to shift the blue light into the near-infrared. An alternative scenario is that the light from the blue component gets extinguished by dust formed by the kilonova and subsequently is re-emitted at near-infrared wavelengths. We test here this hypothesis using the lightcurves of AT 2017gfo, the kilonova accompanying GW170817. We find that of the order of of carbon is required to reproduce the optical/near-infrared lightcurves as the kilonova fades. This putative dust cools from ∼2000 K at ∼4 days after the event to ∼1500 K over the course of the following week, thus requiring dust with a high condensation temperature, such as carbon. We contrast this with the nucleosynthetic yields predicted by a range of kilonova wind models. These suggest that at most of carbon is formed. Moreover, the decay in the inferred dust temperature is slower than that expected in kilonova models. We therefore conclude that in current models of the blue component of the kilonova, the near-infrared component in the kilonova accompanying GW170817 is unlikely to be due to dust.

Funding

C.G. acknowledges support from the Carlsberg Foundation. J.H. is supported by a VILLUM FONDEN Investigator grant (project number 16599). S.R. has been supported by the Swedish Research Council (VR) under grant number 2016-03657_3, by the Swedish National Space Board under grant number Dnr. 107/16, and by the research environment grant "Gravitational Radiation and Electromagnetic Astrophysical Transients (GREAT)" funded by the Swedish Research council (VR) under Dnr. 2016-06012. A.J.L. is supported by STFC and the ERC (grant #725246).

History

Citation

Astrophysical Journal Letters, 2017, 849 (2)

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

VoR (Version of Record)

Published in

Astrophysical Journal Letters

Publisher

American Astronomical Society, IOP Publishing

issn

2041-8205

eissn

2041-8213

Acceptance date

14/10/2017

Copyright date

2017

Available date

10/04/2018

Publisher version

http://iopscience.iop.org/article/10.3847/2041-8213/aa93f9/meta

Language

en