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

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 ($>\! 17\,σ$), and travelling in the plane of the sky, as expected, at an apparent superluminal velocity $V_{app}\sim 4\, c$.