ing that GW170817 produced a successful jet ( Duffell et al . 2018 ) . Using these new data we can also derive robust constraints on the smoothness parameter ( s ) and therefore the sharpness of the light curve peak , something which has not been possible with previously - reported data . Together with the sharpness of the peak , the steep decline indicates that the jet is extremely narrow and that most of the outflow energy of GW170817 resides in the jet . Through simple analytical arguments we are able to place a constraint on the geometry , θ v 8θ j ( θ v 6θ j with semi - analytical modeling ; θ v is the viewing angle and θ j is the jet half - opening angle ) , and implies θ j 5 o if we further use the viewing angle constraint provided by the LIGO - Virgo Collaboration . Using Γ 4 close to the peak of the light curve ( estimated from the observed superluminal motion in GW170817 ) gives θ j 3 o and θ v 15 o .