Troja, E.E.Trojavan Eerten, H.H.van EertenRyan, G.G.RyanRicci, R.R.RicciBurgess, J. M.J. M.BurgessWieringa, M. H.M. H.WieringaPIRO, LUIGILUIGIPIROCenko, S. B.S. B.CenkoSakamoto, T.T.Sakamoto2021-04-132021-04-1320190035-8711http://hdl.handle.net/20.500.12386/30744We present the results of our year-long afterglow monitoring of GW 170817, the first binary neutron star merger detected by Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo. New observations with the Australian Telescope Compact Array and the Chandra X-ray Telescope were used to constrain its late-time behaviour. The broad-band emission, from radio to X-rays, is well-described by a simple power-law spectrum with index β ∼ 0.585 at all epochs. After an initial shallow rise ∝t<SUP>0.9</SUP>, the afterglow displayed a smooth turnover, reaching a peak X-ray luminosity of L<SUB>X</SUB> ≈ 5 × 10<SUP>39</SUP> erg s<SUP>-1</SUP> at 160 d, and has now entered a phase of rapid decline, approximately ∝t<SUP>-2</SUP>. The latest temporal trend challenges most models of choked jet/cocoon systems, and is instead consistent with the emergence of a relativistic structured jet seen at an angle of ≈22° from its axis. Within such model, the properties of the explosion (such as its blast wave energy E<SUB>K</SUB> ≈ 2 × 10<SUP>50</SUP> erg, jet width θ<SUB>c</SUB> ≈ 4°, and ambient density n ≈ 3 × 10<SUP>-3</SUP> cm<SUP>-3</SUP>) fit well within the range of properties of cosmological short gamma-ray bursts.STAMPAenArticle10.1093/mnras/stz22482-s2.0-85074485383000489298100031https://academic.oup.com/mnras/article/489/2/1919/55495292019MNRAS.489.1919TFIS/05 - ASTRONOMIA E ASTROFISICA