The Macronova in GRB 050709 and the GRB-macronova connection

• Published in: Nature communications Vol. 7; no. 1; p. 12898
• Main Authors: Jin, Zhi-Ping, Hotokezaka, Kenta, Li, Xiang, Tanaka, Masaomi, D’Avanzo, Paolo, Fan, Yi-Zhong, Covino, Stefano, Wei, Da-Ming, Piran, Tsvi
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 23.09.2016; Nature Publishing Group; Nature Portfolio
• Subjects: 639/33/34/864; 639/33/34/867; Gravitational waves; Humanities and Social Sciences; Light; multidisciplinary; Observatories; Science; Science (multidisciplinary); Space telescopes; China; Japan
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms12898

GRB 050709 was the first short Gamma-ray Burst (sGRB) with an identified optical counterpart. Here we report a reanalysis of the publicly available data of this event and the discovery of a Li-Paczynski macronova/kilonova that dominates the optical/infrared signal at t >2.5 days. Such a signal would arise from 0.05 r-process material launched by a compact binary merger. The implied mass ejection supports the suggestion that compact binary mergers are significant and possibly main sites of heavy r-process nucleosynthesis. Furthermore, we have reanalysed all afterglow data from nearby short and hybrid GRBs (shGRBs). A statistical study of shGRB/macronova connection reveals that macronova may have taken place in all these GRBs, although the fraction as low as 0.18 cannot be ruled out. The identification of two of the three macronova candidates in the I -band implies a more promising detection prospect for ground-based surveys. A macronova is a clear signature that a short gamma-ray burst has been emitted by a compact-binary merger, but evidence of these events is so far scarce. Here, the authors report signs of a macronova in the optical afterglow of GRB050709, and find similar evidence in other three short bursts.