The unpolarized macronova associated with the gravitational wave event GW170817
Abstract
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.
Cite
@article{arxiv.1710.05849,
title = {The unpolarized macronova associated with the gravitational wave event GW170817},
author = {S. Covino and K. Wiersema and Y. Z. Fan and K. Toma and A. B. Higgins and A. Melandri and P. D'Avanzo and C. G. Mundell and E. Palazzi and N. R. Tanvir and M. G. Bernardini and M. Branchesi and E. Brocato and S. Campana and S. di Serego Alighieri and D. Gotz and J. P. U. Fynbo and W. Gao and A. Gomboc and B. Gompertz and J. Greiner and J. Hjorth and Z. P. Jin and L. Kaper and S. Klose and S. Kobayashi and D. Kopac and C. Kouveliotou and A. J. Levan and J. Mao and D. Malesani and E. Pian and A. Rossi and R. Salvaterra and R. L. C. Starling and I. Steele and G. Tagliaferri and E. Troja and A. J. van der Horst and R. A. M. J. Wijers},
journal= {arXiv preprint arXiv:1710.05849},
year = {2017}
}
Comments
18 pages, 1 figure, 2 tables, Nature Astronomy, in press