SIMBAD references

Macronovae (or kilonovae) are the optical and NIR counterparts of binary neutron star mergers. While the macronova in GW170817 was detected about 10 h after the GW detection, future observations can possibly detect them within the first hour after the merger. Early-time macronovae are potentially powered by some mechanisms such as the beta-decay heating of the surviving free neutrons. In this paper, we propose that polarimetric observation can be a useful tool to study the early macronova emissions. If free nucleons remain in the outermost layer of the ejecta, the electron scattering produces a larger polarization than that by the r-process element-rich ejecta. The degree of polarization can show a large value of ∼ 1-3 per cent for the first 0.3-1 h for free nucleon mass of 10^–5[?\text?]–10^–4 M_☉. Quick polarimetric observations enable us to study not only the aspherical morphology of the ejecta but also the amount of the free nucleons in the ejecta, which is helpful to discriminate the emission mechanisms of the early macronovae.