The outflow structure of GW170817 from late time broadband observations

TL;DR

This study analyzes late-time broadband observations of GW170817, comparing various jet and cocoon models, and identifies promising models that fit the data, suggesting future observations can distinguish between them.

Contribution

It provides the first detailed comparison between cocoon and jet models using extensive broadband data of GW170817, ruling out several models and proposing discriminating future observations.

Findings

Homogeneous and power-law jets are ruled out by data.

Gaussian jet and cocoon with energy injection fit current data.

Future observations can distinguish models by post-peak decay slopes.

Abstract

We present our broadband study of GW170817 from radio to hard X-rays, including NuSTAR and Chandra observations up to 165 days after the merger, and a multi-messenger analysis including LIGO constraints. The data are compared with predictions from a wide range of models, providing the first detailed comparison between non-trivial cocoon and jet models. Homogeneous and power-law shaped jets, as well as simple cocoon models are ruled out by the data, while both a Gaussian shaped jet and a cocoon with energy injection can describe the current dataset for a reasonable range of physical parameters, consistent with the typical values derived from short GRB afterglows. We propose that these models can be unambiguously discriminated by future observations measuring the post-peak behaviour, with slope -1.0 for the cocoon and -2.5 for the jet model.