A very young radio-loud magnetar

arXiv:2004.04083v2
The 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 (${N}_{{\rm{H}}}$ = (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 ${\dot{E}}_{\mathrm{rot}}\sim 1.4\times {10}^{36}$ erg s−1, and characteristic age of 240 yr, the shortest currently known. Archival observations led to an upper limit on the quiescent luminosity
We acknowledge the support of the PHAROS COST Action (CA16214). NR, AB, DV, CD, MR, AGG and VG are supported by the ERC Consolidator Grant “MAGNESIA” (nr.817661) and acknowledge funding from grants SGR2017-1383 and PGC2018-095512-BI00. AB and FCZ are also supported by a Juan de la Cierva fellowship. GLI, SM, AT, and RT acknowledge financial support from the Italian MIUR through PRIN grant 2017LJ39LM. AP, AR, MB and LS acknowledge funding from the grant “iPeska” (INAF PRIN-SKA/CTA; PI Possenti). LS acknowledges funding from ASI-INAF agreements 2017-14-H.O and I/037/12/0.