Coti Zelati, F.F.Coti ZelatiRea, N.N.ReaTurolla, R.R.TurollaPons, J. A.J. A.PonsPAPITTO, ALESSANDROALESSANDROPAPITTOEsposito, P.P.EspositoISRAEL, Gian LucaGian LucaISRAELCAMPANA, SergioSergioCAMPANAZane, S.S.ZaneTiengo, A.A.TiengoMIGNANI, RobertoRobertoMIGNANIMEREGHETTI, SandroSandroMEREGHETTIBaganoff, F. K.F. K.BaganoffHaggard, D.D.HaggardPONTI, GABRIELEGABRIELEPONTITorres, D. F.D. F.TorresBorghese, A.A.BorgheseElfritz, J.J.Elfritz2021-02-092021-02-0920170035-8711http://hdl.handle.net/20.500.12386/30265We report on 3.5 yr of Chandra monitoring of the Galactic Centre magnetar SGR J1745-2900 since its outburst onset in 2013 April. The magnetar spin-down has shown at least two episodes of period derivative increases so far, and it has slowed down regularly in the past year or so. We observed a slightly increasing trend in the time evolution of the pulsed fraction, up to ∼55 per cent in the most recent observations. SGR J1745-2900 has not reached the quiescent level yet, and so far the overall outburst evolution can be interpreted in terms of a cooling hot region on the star surface. We discuss possible scenarios, showing in particular how the presence of a shrinking hotspot in this source is hardly reconcilable with internal crustal cooling and favours the untwisting bundle model for this outburst. Moreover, we also show how the emission from a single uniform hotspot is incompatible with the observed pulsed fraction evolution for any pair of viewing angles, suggesting an anisotropic emission pattern.STAMPAenArticle10.1093/mnras/stx17002-s2.0-85038870711000409022700034https://academic.oup.com/mnras/article/471/2/1819/39308662017MNRAS.471.1819CFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation