Troja, E.E.TrojaPIRO, LUIGILUIGIPIRORyan, G.G.Ryanvan Eerten, H.H.van EertenRICCI, ROBERTOROBERTORICCIWieringa, M. H.M. H.WieringaLOTTI, SimoneSimoneLOTTISakamoto, T.T.SakamotoCenko, S. B.S. B.Cenko2021-04-292021-04-2920181745-3925http://hdl.handle.net/20.500.12386/30946We present our broad-band study of GW170817 from radio to hard X-rays, including NuSTAR and Chandra observations up to 165 d after the merger, and a multimessenger 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 data set 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 F<SUB>ν</SUB> ∝ t<SUP>∼-1.0</SUP> for the cocoon and F<SUB>ν</SUB>∝ t<SUP>∼-2.5</SUP> for the jet model.STAMPAenArticle10.1093/mnrasl/sly0612-s2.0-85048519232http://arxiv.org/abs/1801.06516v2https://academic.oup.com/mnrasl/article/478/1/L18/49699812018MNRAS.478L..18TFIS/05 - ASTRONOMIA E ASTROFISICA