The Macronova in GRB 050709 and the GRB/macronova connection

TL;DR

This paper re-analyzes data from GRB 050709, discovering a macronova/kilonova signal indicating significant r-process material ejection, supporting the role of compact binary mergers in heavy element synthesis and suggesting a common occurrence in short GRBs.

Contribution

It provides the first re-analysis confirming a macronova in GRB 050709 and explores the widespread presence of macronovae in short GRBs through statistical analysis.

Findings

Detection of a macronova/kilonova in GRB 050709.

Evidence supporting compact binary mergers as main r-process sites.

Potential for ground-based detection of macronovae in short GRBs.

Abstract

GRB 050709 was the first short Gamma-ray Burst (sGRB) with an identified optical afterglow. In this work we report a re-analysis of the publicly available data of this event and the discovery of a Li-Paczynski macronova/kilonova that dominates the optical/IR signal at t $>$ 2.5 days. Such a signal would arise from ~0.05 M$_\odot$ 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. We have re-analyzed all afterglow data from nearby short and hybrid GRBs. A statistical study of sGRB/macronova connection reveals that macronova may have taken place in all these GRBs though 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.