The Macronova in GRB 050709 and the GRB-macronova connection

Abstract

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.

Neutron Star–Black Hole Coalescence Rate Inferred from Macronova Observations

“…A macronova model light curve generated from numerical simulation for the ejecta from an NS−BH coalescence, with a velocity ∼ 0.2c and mass M ej ∼ 0.1M ⊙ , can reasonably reproduce the "excess" displayed in hGRB 060614 [30]. The same model works also for the macronova signal displaying in sGRB 050709 with a M ej ∼ 0.05 M ⊙ [31]. To reproduce the macronova signal in sGRB 130603B within the BNS coalescence scenario, an unusual large M ej ∼ 0.03 − 0.08 M ⊙ is needed [32].…”

“…Jet breaks had been reliably measured in GRB 060614 and GRB 130603B and θ j ≈ 0.1 rad were inferred [16,34]. For GRB 050709 the recent analysis suggests that an early jet break appeared at t ≤ 1.4 days [31], implying a θ j ≤ 0.1 rad.…”

“…To reproduce the macronova signal in sGRB 130603B within the BNS coalescence scenario, an unusual large M ej ∼ 0.03 − 0.08 M ⊙ is needed [32]. Instead, such a signal can be naturally reproduced within the NS−BH coalescence scenario for a M ej ∼ 0.05 M ⊙ [26,31,33]. Encouragingly, all three GRB/macronova events have very small offsets from their hosts, as suggested by Troja et al [15] for NS−BH coalescence events.…”

Neutron-Star Implosions as Heavy-Element Sources

“…Sensitivity similar to aLIGO is expected in the upcoming Advanced Virgo [82] (aVirgo) and KAGRA [83] experiments. A recent analysis of kilonovae [84] also exhibits tension with observations and highlights the need for an extremely efficient ejection of r-process material in the COM scenario.…”

Maximizing the Detection Probability of Kilonovae Associated With Gravitational Wave Observations

“…However, more recent calculations including the opacity of the r − process elements (Barnes & Kasen 2013;Tanaka et al 2014;Grossman et al 2014) indicate that this timescale is likely to be days to weeks. Currently, there are three detections associated with the short-duration gamma-ray bursts GRB 130603B (Tanvir et al 2013;Berger et al 2013) and GRB 060614 (Yang et al 2015;Jin et al 2015) and GRB 050709 (Jin et al 2016).…”