The gravitational wave and short gamma-ray burst GW170817/SHB170817A, not your everyday binary neutron star merger

TL;DR

This paper discusses the unique GW170817/SHB170817A event, confirming gravitational wave predictions from neutron star mergers and providing strong evidence for the cannonball model of gamma-ray bursts over the standard fireball model.

Contribution

It presents observational evidence favoring the cannonball model for gamma-ray bursts, contrasting with the traditional fireball model, based on multi-wavelength data from a unique neutron star merger event.

Findings

Radio observations detected a cannonball with >17σ significance.

The cannonball traveled at an apparent superluminal velocity of ~4c.

Electromagnetic observations challenge the standard fireball model.

Abstract

This event, so far unique, beautifully confirmed the standard views on the gravitational waves produced by a merger of two neutron stars, but its electromagnetic multi-wavelenth observations disagreed with the numerous initial versions of the "standard fireball model(s)" of gamma ray bursts. Contrariwise, they provided strong evidence in favour of the "cannonball" model. Most uncontroversially, a cannonball was observed at radio wavelengths, with an overwhelming statistical significance ($>\! 17\,\sigma$), and travelling in the plane of the sky, as expected, at an apparent superluminal velocity $V_{app}\sim 4\, c$.