The unpolarized macronova associated with the gravitational wave event GW170817

Oct 16, 2017
4 pages
Published in:
  • Nature Astron. 1 (2017) 11, 791-794,
  • Nature Astron. 1 (2017) 11, 805 (erratum)
  • Published: Oct 30, 2017
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Abstract: (Springer)
The merger of two dense stellar remnants including at least one neutron star is predicted to produce gravitational waves (GWs) and short-duration gamma ray bursts 1,^{,}2 . In the process, neutron-rich material is ejected from the system and heavy elements are synthesized by r-process nucleosynthesis 1,^{,}3 . The radioactive decay of these heavy elements produces additional transient radiation termed kilonova or macronova 4^{–}10 . We report the detection of linear optical polarization, P = (0.50 ± 0.07)%, 1.46 days after detection of the GWs from GW 170817—a double neutron star merger associated with an optical macronova counterpart and a short gamma ray burst 11^{–}14 . 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 in heavy elements—the lanthanides 15 . The polarization measurement was made when the macronova was still in its blue phase, during which there was 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.
Note:
  • 18 pages, 1 figure, 2 tables, Nature Astronomy, in press
  • gamma ray: burst
  • polarization: optical
  • upper limit
  • gravitational radiation
  • neutron star
  • nucleosynthesis
  • radioactivity
  • decay
  • geometry
  • galaxy
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