The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta
We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational-wave (GW) source, the binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 and 9.5 days post-merger, using the Southern Astrophysical Research and Magellan telescopes; the...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Journal Article |
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Institute of Physics Publishing
2017
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| Online Access: | http://hdl.handle.net/20.500.11937/73441 |
| _version_ | 1848763014346440704 |
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| author | Nicholl, M. Berger, E. Kasen, D. Metzger, B. Elias, J. Briceño, C. Alexander, K. Blanchard, P. Chornock, R. Cowperthwaite, P. Eftekhari, T. Fong, W. Margutti, R. Villar, V. Williams, P. Brown, W. Annis, J. Bahramian, Arash Brout, D. Brown, D. Chen, H. Clemens, J. Dennihy, E. Dunlap, B. Holz, D. Marchesini, E. Massaro, F. Moskowitz, N. Pelisoli, I. Rest, A. Ricci, F. Sako, M. Soares-Santos, M. Strader, J. |
| author_facet | Nicholl, M. Berger, E. Kasen, D. Metzger, B. Elias, J. Briceño, C. Alexander, K. Blanchard, P. Chornock, R. Cowperthwaite, P. Eftekhari, T. Fong, W. Margutti, R. Villar, V. Williams, P. Brown, W. Annis, J. Bahramian, Arash Brout, D. Brown, D. Chen, H. Clemens, J. Dennihy, E. Dunlap, B. Holz, D. Marchesini, E. Massaro, F. Moskowitz, N. Pelisoli, I. Rest, A. Ricci, F. Sako, M. Soares-Santos, M. Strader, J. |
| author_sort | Nicholl, M. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational-wave (GW) source, the binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 and 9.5 days post-merger, using the Southern Astrophysical Research and Magellan telescopes; the UV spectrum was obtained with the Hubble Space Telescope at 5.5 days. Our data reveal a rapidly fading blue component (T ≈ 5500 K at 1.5 days) that quickly reddens; spectra later than >~4.5 days peak beyond the optical regime. The spectra are mostly featureless, although we identify a possible weak emission line at ~7900 Å at >~4.5 days. The colors, rapid evolution, and featureless spectrum are consistent with a "blue" kilonova from polar ejecta comprised mainly of light r-process nuclei with atomic mass number A<~4.5. This indicates a sightline within θobs <~ 45°
of the orbital axis. Comparison to models suggests ~0.03 M ⊙ of blue ejecta, with a velocity of ~0.3c. The required lanthanide fraction is ~ 10-4, but this drops to <10-5. in the outermost ejecta. The large velocities point to a dynamical origin, rather than a disk wind, for this blue component, suggesting that both binary constituents are neutron stars (as opposed to a binary consisting of a neutron star and a black hole). For dynamical ejecta, the high mass favors a small neutron star radius of <~12 km. This mass also supports the idea that neutron star mergers are a major contributor to r-process nucleosynthesis. |
| first_indexed | 2025-11-14T10:56:43Z |
| format | Journal Article |
| id | curtin-20.500.11937-73441 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T10:56:43Z |
| publishDate | 2017 |
| publisher | Institute of Physics Publishing |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-734412019-05-09T03:34:08Z The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta Nicholl, M. Berger, E. Kasen, D. Metzger, B. Elias, J. Briceño, C. Alexander, K. Blanchard, P. Chornock, R. Cowperthwaite, P. Eftekhari, T. Fong, W. Margutti, R. Villar, V. Williams, P. Brown, W. Annis, J. Bahramian, Arash Brout, D. Brown, D. Chen, H. Clemens, J. Dennihy, E. Dunlap, B. Holz, D. Marchesini, E. Massaro, F. Moskowitz, N. Pelisoli, I. Rest, A. Ricci, F. Sako, M. Soares-Santos, M. Strader, J. We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational-wave (GW) source, the binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 and 9.5 days post-merger, using the Southern Astrophysical Research and Magellan telescopes; the UV spectrum was obtained with the Hubble Space Telescope at 5.5 days. Our data reveal a rapidly fading blue component (T ≈ 5500 K at 1.5 days) that quickly reddens; spectra later than >~4.5 days peak beyond the optical regime. The spectra are mostly featureless, although we identify a possible weak emission line at ~7900 Å at >~4.5 days. The colors, rapid evolution, and featureless spectrum are consistent with a "blue" kilonova from polar ejecta comprised mainly of light r-process nuclei with atomic mass number A<~4.5. This indicates a sightline within θobs <~ 45° of the orbital axis. Comparison to models suggests ~0.03 M ⊙ of blue ejecta, with a velocity of ~0.3c. The required lanthanide fraction is ~ 10-4, but this drops to <10-5. in the outermost ejecta. The large velocities point to a dynamical origin, rather than a disk wind, for this blue component, suggesting that both binary constituents are neutron stars (as opposed to a binary consisting of a neutron star and a black hole). For dynamical ejecta, the high mass favors a small neutron star radius of <~12 km. This mass also supports the idea that neutron star mergers are a major contributor to r-process nucleosynthesis. 2017 Journal Article http://hdl.handle.net/20.500.11937/73441 10.3847/2041-8213/aa9029 Institute of Physics Publishing restricted |
| spellingShingle | Nicholl, M. Berger, E. Kasen, D. Metzger, B. Elias, J. Briceño, C. Alexander, K. Blanchard, P. Chornock, R. Cowperthwaite, P. Eftekhari, T. Fong, W. Margutti, R. Villar, V. Williams, P. Brown, W. Annis, J. Bahramian, Arash Brout, D. Brown, D. Chen, H. Clemens, J. Dennihy, E. Dunlap, B. Holz, D. Marchesini, E. Massaro, F. Moskowitz, N. Pelisoli, I. Rest, A. Ricci, F. Sako, M. Soares-Santos, M. Strader, J. The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta |
| title | The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta |
| title_full | The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta |
| title_fullStr | The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta |
| title_full_unstemmed | The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta |
| title_short | The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta |
| title_sort | electromagnetic counterpart of the binary neutron star merger ligo/virgo gw170817. iii. optical and uv spectra of a blue kilonova from fast polar ejecta |
| url | http://hdl.handle.net/20.500.11937/73441 |