Swift and NuSTAR observations of GW170817: detection of a blue kilonova

P. A. Evans; S. B. Cenko; J. A. Kennea; S. W. K. Emery; N. P. M. Kuin; O. Korobkin; R. T. Wollaeger; C. L. Fryer; K. K. Madsen; F. A. Harrison; Y. Xu; E. Nakar; K. Hotokezaka; A. Lien; S. Campana; S. R. Oates; E. Troja; A. A. Breeveld; F. E. Marshall; S. D. Barthelmy; A. P. Beardmore; D. N. Burrows; G. Cusumano; A. D'Ai; P. D'Avanzo; V. D'Elia; M. de Pasquale; W. P. Even; C. J. Fontes; K. Forster; J. Garcia; P. Giommi; B. Grefenstette; C. Gronwall; D. H. Hartmann; M. Heida; A. L. Hungerford; M. M. Kasliwal; H. A. Krimm; A. J. Levan; D. Malesani; A. Melandri; H. Miyasaka; J. A. Nousek; P. T. O'Brien; J. P. Osborne; C. Pagani; K. L. Page; D. M. Palmer; M. Perri; S. Pike; J. L. Racusin; S. Rosswog; M. H. Siegel; T. Sakamoto; B. Sbarufatti; G. Tagliaferri; N. R. Tanvir; A. Tohuvavohu

doi:10.1126/science.aap9580

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arXiv · 1710.05437

Swift and NuSTAR observations of GW170817: detection of a blue kilonova

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Abstract

With the first direct detection of merging black holes in 2015, the era of gravitational wave (GW) astrophysics began. A complete picture of compact object mergers, however, requires the detection of an electromagnetic (EM) counterpart. We report ultraviolet (UV) and X-ray observations by Swift and the Nuclear Spectroscopic Telescope ARray (NuSTAR) of the EM counterpart of the binary neutron star merger GW170817. The bright, rapidly fading ultraviolet emission indicates a high mass ($\approx0.03$ solar masses) wind-driven outflow with moderate electron fraction ($Y_{e}\approx0.27$). Combined with the X-ray limits, we favor an observer viewing angle of $\approx 30^{\circ}$ away from the orbital rotation axis, which avoids both obscuration from the heaviest elements in the orbital plane and a direct view of any ultra-relativistic, highly collimated ejecta (a gamma-ray burst afterglow).

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P. A. Evans, S. B. Cenko, J. A. Kennea, S. W. K. Emery, N. P. M. Kuin, O. Korobkin, R. T. Wollaeger, C. L. Fryer, K. K. Madsen, F. A. Harrison, Y. Xu, E. Nakar, K. Hotokezaka, A. Lien, S. Campana, S. R. Oates, E. Troja, A. A. Breeveld, F. E. Marshall, S. D. Barthelmy, A. P. Beardmore, D. N. Burrows, G. Cusumano, A. D'Ai, P. D'Avanzo, V. D'Elia, M. de Pasquale, W. P. Even, C. J. Fontes, K. Forster, J. Garcia, P. Giommi, B. Grefenstette, C. Gronwall, D. H. Hartmann, M. Heida, A. L. Hungerford, M. M. Kasliwal, H. A. Krimm, A. J. Levan, D. Malesani, A. Melandri, H. Miyasaka, J. A. Nousek, P. T. O'Brien, J. P. Osborne, C. Pagani, K. L. Page, D. M. Palmer, M. Perri, S. Pike, J. L. Racusin, S. Rosswog, M. H. Siegel, T. Sakamoto, B. Sbarufatti, G. Tagliaferri, N. R. Tanvir, A. Tohuvavohu. 2017-10-16. Swift and NuSTAR observations of GW170817: detection of a blue kilonova. https://doi.org/10.1126/science.aap9580

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