A Neutron Star Binary Merger Model for GW170817/GRB170817a/SSS17a

TL;DR

This paper models GW170817 as a neutron star merger producing multi-wavelength emissions, exploring whether the observed signals are from a low-luminosity or off-axis short gamma-ray burst, and emphasizes the need for detailed follow-up observations.

Contribution

It presents a comprehensive model linking gravitational wave and electromagnetic observations of GW170817, analyzing the nature of the relativistic ejecta and emission mechanisms.

Findings

Consistent with a low-luminosity short gamma-ray burst or an off-axis powerful sGRB.

Multi-wavelength data probe different merger components and ejecta.

Follow-up observations are crucial for constraining ejecta properties.

Abstract

The merging neutron star gravitational wave event GW170817 has been observed throughout the entire electromagnetic spectrum from radio waves to $\gamma$-rays. The resulting energetics, variability, and light curves are shown to be consistent with GW170817 originating from the merger of two neutron stars, in all likelihood followed by the prompt gravitational collapse of the massive remnant. The available $\gamma$-ray, X-ray and radio data provide a clear probe for the nature of the relativistic ejecta and the non-thermal processes occurring within, while the ultraviolet, optical and infrared emission are shown to probe material torn during the merger and subsequently heated by the decay of freshly synthesized $r$-process material. The simplest hypothesis that the non-thermal emission is due to a low-luminosity short $\gamma$-ray burst (sGRB) seems to agree with the present data. While low luminosity sGRBs might be common, we show here that the collective prompt and multi-wavelength observations are also consistent with a typical, powerful sGRB seen off-axis. Detailed follow-up observations are thus essential before we can place stringent constraints on the nature of the relativistic ejecta in GW170817.