Borghese, A.A.BorgheseRea, N.N.ReaTurolla, R.R.TurollaRIGOSELLI, MICHELAMICHELARIGOSELLIAlford, J. A. J.J. A. J.AlfordGotthelf, E. V.E. V.GotthelfBURGAY, MARTAMARTABURGAYPOSSENTI, ANDREAANDREAPOSSENTIZane, S.S.ZaneCoti Zelati, F.F.Coti ZelatiPerna, R.R.PernaEsposito, P.P.EspositoMereghetti, S.S.MereghettiViganò, D.D.ViganòTIENGO, ANDREAANDREATIENGOGötz, D.D.GötzIbrahim, A.A.IbrahimISRAEL, Gian LucaGian LucaISRAELPons, J.J.PonsSathyaprakash, R.R.Sathyaprakash2022-06-012022-06-0120210035-8711http://hdl.handle.net/20.500.12386/32171After 15 yr, in late 2018, the magnetar XTE J1810-197 underwent a second recorded X-ray outburst event and reactivated as a radio pulsar. We initiated an X-ray monitoring campaign to follow the timing and spectral evolution of the magnetar as its flux decays using Swift, XMM-Newton, NuSTAR, and NICER observations. During the year-long campaign, the magnetar reproduced similar behaviour to that found for the first outburst, with a factor of 2 change in its spin-down rate from ~7.2 × 10<SUP>-12</SUP> to ~1.5 × 10<SUP>-11</SUP> s s<SUP>-1</SUP> after two months. Unique to this outburst, we confirm the peculiar energy-dependent phase shift of the pulse profile. Following the initial outburst, the spectrum of XTE J1810-197 is well modelled by multiple blackbody components corresponding to a pair of non-concentric, hot thermal caps surrounded by a cooler one, superposed to the colder star surface. We model the energy-dependent pulse profile to constrain the viewing and surface emission geometry and find that the overall geometry of XTE J1810-197 has likely evolved relative to that found for the 2003 event.STAMPAen10.1093/mnras/stab1236https://academic.oup.com/mnras/article/504/4/5244/6261201?login=false2021MNRAS.504.5244BFIS/05 - ASTRONOMIA E ASTROFISICA