GRB 111005A at Z = 0.0133 and the Prospect of Establishing Long-short GRB/GW Association

TL;DR

This paper investigates the nature of the long-short gamma-ray burst GRB 111005A, suggesting it originated from a neutron star merger with low ejecta mass, and discusses how joint gravitational wave and gamma-ray observations can confirm such origins.

Contribution

It proposes a neutron star merger model for GRB 111005A, emphasizing the importance of joint GW and gamma-ray observations to identify long-short GRB origins.

Findings

GRB 111005A likely resulted from a neutron star merger with low ejecta mass.

Non-detection of optical/infrared emission constrains ejecta mass to ≤ 0.01 M_sun.

Joint GW and gamma-ray observations can test the neutron star merger origin of lsGRBs.

Abstract

GRB 111005A, one long duration gamma-ray burst (GRB) occurred within a metal-rich environment that lacks massive stars with $M_{\rm ZAMS}\geq 15M_\odot$, is not coincident with supernova emission down to stringent limit and thus should be classified as a "long-short" GRB (lsGRB; also known as SN-less long GRB or hybrid GRB), like GRB 060505 and GRB 060614. In this work we show that in the neutron star merger model, the non-detection of the optical/infrared emission of GRB 111005A requires a sub-relativistic neutron-rich ejecta with the mass of $\leq 0.01~M_\odot$, (significantly) less massive than that of GRB 130603B, GRB 060614 and GRB 050709. The lsGRBs are found to have a high rate density and the neutron star merger origin model can be unambiguously tested by the joint observations of the second generation gravitational wave (GW) detectors and the full-sky gamma-ray monitors such as Fermi-GBM and the proposing GECAM. If no lsGRB/GW association is observed in 2020s, alternative scenarios have to be systematically investigated. With the detailed environmental information achievable for the very-nearby events, a novel kind of merger or explosion origin may be identified.