GHIRLANDA, GiancarloGiancarloGHIRLANDASalafia, Om SharanOm SharanSalafiaParagi, Z.Z.ParagiGiroletti, M.M.GirolettiYang, J.J.YangMarcote, B.B.MarcoteBlanchard, J.J.BlanchardAgudo, I.I.AgudoAn, T.T.AnBERNARDINI, Maria GraziaMaria GraziaBERNARDINIBeswick, R.R.BeswickBranchesi, M.M.BranchesiCAMPANA, SergioSergioCAMPANACasadio, C.C.CasadioChassande-Mottin, E.E.Chassande-MottinColpi, M.M.ColpiCOVINO, StefanoStefanoCOVINOD'AVANZO, PaoloPaoloD'AVANZOD'Elia, V.V.D'EliaFrey, S.S.FreyGawronski, M.M.GawronskiGHISELLINI, GabrieleGabrieleGHISELLINIGurvits, L. I.L. I.GurvitsJonker, P. G.P. G.Jonkervan Langevelde, H. J.H. J.van LangeveldeMELANDRI, AndreaAndreaMELANDRIMoldon, J.J.MoldonNava, L.L.NavaPerego, A.A.PeregoPerez-Torres, M. A.M. A.Perez-TorresReynolds, C.C.ReynoldsSALVATERRA, RubenRubenSALVATERRATAGLIAFERRI, GianpieroGianpieroTAGLIAFERRIVENTURI, TizianaTizianaVENTURIVergani, S. D.S. D.VerganiZhang, M.M.Zhang2020-12-232020-12-2320190036-8075http://hdl.handle.net/20.500.12386/29141The binary neutron star merger event GW170817 was detected through both electromagnetic radiation and gravitational waves. Its afterglow emission may have been produced by either a narrow relativistic jet or an isotropic outflow. High-spatial-resolution measurements of the source size and displacement can discriminate between these scenarios. We present very-long-baseline interferometry observations, performed 207.4 days after the merger by using a global network of 32 radio telescopes. The apparent source size is constrained to be smaller than 2.5 milli-arc seconds at the 90% confidence level. This excludes the isotropic outflow scenario, which would have produced a larger apparent size, indicating that GW170817 produced a structured relativistic jet. Our rate calculations show that at least 10% of neutron star mergers produce such a jet.STAMPAenArticle10.1126/science.aau88152-s2.0-85062385835000460194200043https://science.sciencemag.org/content/363/6430/968https://arxiv.org/abs/1808.004692019Sci...363..968GFIS/05 - ASTRONOMIA E ASTROFISICA