Esposito, P.P.EspositoRea, N.N.ReaBorghese, A.A.BorgheseZelati, F. CotiF. CotiZelatiViganò, D.D.ViganòISRAEL, Gian LucaGian LucaISRAELTiengo, A.A.TiengoRIDOLFI, ALESSANDROALESSANDRORIDOLFIPOSSENTI, ANDREAANDREAPOSSENTIBURGAY, MARTAMARTABURGAYGötz, D.D.GötzPintore, FabioFabioPintoreSTELLA, LuigiLuigiSTELLADehman, C.C.DehmanRonchi, M.M.RonchiCAMPANA, SergioSergioCAMPANAGarcia-Garcia, A.A.Garcia-GarciaGraber, V.V.GraberMEREGHETTI, SandroSandroMEREGHETTIPerna, R.R.PernaCastillo, G. A. RodríguezG. A. RodríguezCastilloTurolla, R.R.TurollaZane, S.S.Zane2021-01-192021-01-1920202041-8205http://hdl.handle.net/20.500.12386/29845The magnetar Swift J1818.0-1607 was discovered in 2020 March when Swift detected a 9 ms hard X-ray burst and a long-lived outburst. Prompt X-ray observations revealed a spin period of 1.36 s, soon confirmed by the discovery of radio pulsations. We report here on the analysis of the Swift burst and follow-up X-ray and radio observations. The burst average luminosity was Lburst ∼ 2 × 1039 erg s-1 (at 4.8 kpc). Simultaneous observations with XMM-Newton and NuSTAR three days after the burst provided a source spectrum well fit by an absorbed blackbody ( NH = (1.13 ± 0.03) × 1023 cm-2 and kT = 1.16 ± 0.03 keV) plus a power law (Γ = 0.0 ± 1.3) in the 1-20 keV band, with a luminosity of ∼8 × 1034 erg s-1, dominated by the blackbody emission. From our timing analysis, we derive a dipolar magnetic field B ∼ 7 × 1014 G, spin-down luminosity E˙rot∼1.4×1036 erg s-1, and characteristic age of 240 yr, the shortest currently known. Archival observations led to an upper limit on the quiescent luminosity <5.5 × 1033 erg s-1, lower than the value expected from magnetar cooling models at the source characteristic age. A 1 hr radio observation with the Sardinia Radio Telescope taken about 1 week after the X-ray burst detected a number of strong and short radio pulses at 1.5 GHz, in addition to regular pulsed emission; they were emitted at an average rate 0.9 min-1 and accounted for ∼50% of the total pulsed radio fluence. We conclude that Swift J1818.0-1607 is a peculiar magnetar belonging to the small, diverse group of young neutron stars with properties straddling those of rotationally and magnetically powered pulsars. Future observations will make a better estimation of the age possible by measuring the spin-down rate in quiescence.STAMPAenArticle10.3847/2041-8213/ab97422-s2.0-85087006107000543268200001https://iopscience.iop.org/article/10.3847/2041-8213/ab97422020ApJ...896L..30EFIS/05 - ASTRONOMIA E ASTROFISICA