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A kilonova as the electromagnetic counterpart to a gravitational-wave source

A kilonova as the electromagnetic counterpart to a gravitational-wave source
A kilonova as the electromagnetic counterpart to a gravitational-wave source
Gravitational waves were discovered with the detection of binary black-hole mergers1 and they should also be detectable from lower-mass neutron-star mergers. These are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal. This signal is luminous at optical and infrared wavelengths and is called a kilonova2,3,4,5. The gravitational-wave source GW170817 arose from a binary neutron-star merger in the nearby Universe with a relatively well confined sky position and distance estimate6. Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC 4993, which is spatially coincident with GW170817 and with a weak, short γ-ray burst7,8. The transient has physical parameters that broadly match the theoretical predictions of blue kilonovae from neutron-star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 ± 0.01 solar masses, with an opacity of less than 0.5 square centimetres per gram, at a velocity of 0.2 ± 0.1 times light speed. The power source is constrained to have a power-law slope of −1.2 ± 0.3, consistent with radioactive powering from r-process nuclides. (The r-process is a series of neutron capture reactions that synthesise many of the elements heavier than iron.) We identify line features in the spectra that are consistent with light r-process elements (atomic masses of 90–140). As it fades, the transient rapidly becomes red, and a higher-opacity, lanthanide-rich ejecta component may contribute to the emission. This indicates that neutron-star mergers produce gravitational waves and radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements.
0028-0836
75-79
Smartt, S.J.
b940cb45-a56d-407d-882d-d8f95c63749c
Chen, T.-W.
55ae0c1b-67c7-4dba-b058-5bf8c7a77c10
Jerkstrand, A.
8d69b4b6-5293-4344-be3e-bb0f32e51f27
Sullivan, Mark
2f31f9fa-8e79-4b35-98e2-0cb38f503850
et al.
Smartt, S.J.
b940cb45-a56d-407d-882d-d8f95c63749c
Chen, T.-W.
55ae0c1b-67c7-4dba-b058-5bf8c7a77c10
Jerkstrand, A.
8d69b4b6-5293-4344-be3e-bb0f32e51f27
Sullivan, Mark
2f31f9fa-8e79-4b35-98e2-0cb38f503850

Smartt, S.J., Chen, T.-W., Jerkstrand, A. and Sullivan, Mark , et al. (2017) A kilonova as the electromagnetic counterpart to a gravitational-wave source. Nature, 551, 75-79. (doi:10.1038/nature24303).

Record type: Article

Abstract

Gravitational waves were discovered with the detection of binary black-hole mergers1 and they should also be detectable from lower-mass neutron-star mergers. These are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal. This signal is luminous at optical and infrared wavelengths and is called a kilonova2,3,4,5. The gravitational-wave source GW170817 arose from a binary neutron-star merger in the nearby Universe with a relatively well confined sky position and distance estimate6. Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC 4993, which is spatially coincident with GW170817 and with a weak, short γ-ray burst7,8. The transient has physical parameters that broadly match the theoretical predictions of blue kilonovae from neutron-star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 ± 0.01 solar masses, with an opacity of less than 0.5 square centimetres per gram, at a velocity of 0.2 ± 0.1 times light speed. The power source is constrained to have a power-law slope of −1.2 ± 0.3, consistent with radioactive powering from r-process nuclides. (The r-process is a series of neutron capture reactions that synthesise many of the elements heavier than iron.) We identify line features in the spectra that are consistent with light r-process elements (atomic masses of 90–140). As it fades, the transient rapidly becomes red, and a higher-opacity, lanthanide-rich ejecta component may contribute to the emission. This indicates that neutron-star mergers produce gravitational waves and radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements.

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Accepted/In Press date: 26 September 2017
e-pub ahead of print date: 16 October 2017

Identifiers

Local EPrints ID: 416290
URI: https://eprints.soton.ac.uk/id/eprint/416290
ISSN: 0028-0836
PURE UUID: d05a6325-bb0b-411a-ba04-d07f9f938759
ORCID for Mark Sullivan: ORCID iD orcid.org/0000-0001-9053-4820

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Date deposited: 11 Dec 2017 17:30
Last modified: 17 Jul 2019 17:48

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