PIRO, LUIGILUIGIPIROTroja, E.E.TrojaZhang, B.B.ZhangRyan, G.G.Ryanvan Eerten, H.H.van EertenRicci, R.R.RicciWieringa, M. H.M. H.WieringaTiengo, A.A.TiengoButler, N. R.N. R.ButlerCenko, S. B.S. B.CenkoFox, O. D.O. D.FoxKhandrika, H. G.H. G.KhandrikaNovara, G.G.NovaraROSSI, AndreaAndreaROSSISakamoto, T.T.Sakamoto2021-04-132021-04-1320190035-8711http://hdl.handle.net/20.500.12386/30745Multimessenger observations of GW170817 have not conclusively established whether the merger remnant is a black hole (BH) or a neutron star (NS). We show that a long-lived magnetized NS with a poloidal field B ≈ 10<SUP>12</SUP> G is fully consistent with the electromagnetic dataset, when spin-down losses are dominated by gravitational wave (GW) emission. The required ellipticity ∊ ≳ 10<SUP>-5</SUP> can result from a toroidal magnetic field component much stronger than the poloidal component, a configuration expected from an NS newly formed from a merger. Abrupt magnetic dissipation of the toroidal component can lead to the appearance of X-ray flares, analogous to the one observed in gamma-ray burst (GRB) afterglows. In the X-ray afterglow of GW170817, we identify a low-significance (≳3σ) temporal feature at 155 d, consistent with a sudden reactivation of the central NS. Energy injection from the NS spin-down into the relativistic shock is negligible, and the underlying continuum is fully accounted for by a structured jet seen off-axis. Whereas radio and optical observations probe the interaction of this jet with the surrounding medium, observations at X-ray wavelengths, performed with adequate sampling, open a privileged window on to the merger remnant.STAMPAenArticle10.1093/mnras/sty30472-s2.0-85060219618000462258200036https://academic.oup.com/mnras/article/483/2/1912/51844832019MNRAS.483.1912PFIS/05 - ASTRONOMIA E ASTROFISICA