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The unpolarized macronova associated with the gravitational wave event GW170817

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journal contribution
posted on 27.11.2017, 14:31 by S. Covino, K. Wiersema, Y. Z. Fan, K. Toma, A. B. Higgins, A. Melandri, P. D'Avanzo, C. G. Mundell, E. Palazzi, N. R. Tanvir, M. G. Bernardini, M. Branchesi, E. Brocato, S. Campana, S. D. S. Alighieri, D. Götz, J. P. U. Fynbo, W. Gao, A. Gomboc, B. Gompertz, J. Greiner, J. Hjorth, Z. P. Jin, L. Kaper, S. Klose, S. Kobayashi, D. Kopac, C. Kouveliotou, A. J. Levan, J. Mao, D. Malesani, E. Pian, A. Rossi, R. Salvaterra, R. L. C. Starling, I. Steele, G. Tagliaferri, E. Troja, A. J. V. D. Horst, R. A. M. J. Wijers
The merger of two dense stellar remnants including at least one neutron star (NS) is predicted to produce gravitational waves (GWs) and short duration gamma ray bursts (GRBs). In the process, neutron-rich material is ejected from the system and heavy elements are synthesized by r-process nucleosynthesis. The radioactive decay of these heavy elements produces additional transient radiation termed "kilonova" or "macronova". We report the detection of linear optical polarization P = (0.50 +/- 0.07)% at 1.46 days after detection of the GWs from GW170817, a double neutron star merger associated with an optical macronova counterpart and a short GRB. The optical emission from a macronova is expected to be characterized by a blue, rapidly decaying, component and a red, more slowly evolving, component due to material rich of heavy elements, the lanthanides. The polarization measurement was made when the macronova was still in its blue phase, during which there is an important contribution from a lanthanide-free outflow. The low degree of polarization is consistent with intrinsically unpolarized emission scattered by Galactic dust, suggesting a symmetric geometry of the emitting region and low inclination of the merger system. Stringent upper limits to the polarization degree from 2.45 - 9.48 days post-burst are consistent with the lanthanides-rich macronova interpretation.


This study was based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under European Southern Observatory programme 099.D-0116. We thank the European Southern Observatory—Paranal staff for carrying out excellent observations under difficult conditions during a hectic period. We also acknowledge partial funding from Agenzia Spaziale Italiana-Istituto Nazionale di Astrofisica grant I/004/11/3. K.W., A.B.H., R.L.C.S. and N.R.T. acknowledge funding from the Science and Technology Facilities Council. J.H. was supported by a VILLUM FONDEN Investigator grant (project number 16599). Y.Z.F. was supported by the National Natural Science Foundation of China under grant 11525313. C.G.M. acknowledges support from the UK Science and Technology Facilities Council. K.T. was supported by Japan Society for the Promotion of Science grant 15H05437 and a Japan Science and Technology Consortia grant. J.M. acknowledges the National Natural Science Foundation of China 11673062 and the Major Program of the Chinese Academy of Sciences(KJZD-EW-M06).



Nature Astronomy 2017, 1, pp. 791–794

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


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Nature Astronomy 2017


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