The unpolarized macronova associated with the gravitational wave event GW170817

Understand

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.