Swift J1818.0-1607 is a new radio-loud magnetar discovered by the Swift Burst Alert Telescope on 2020 March 12. It has a magnetic field B~2.5e14 G, spin-down luminosity of 7.2e35 ergs/s, and characteristic age of ~470yr. Here we report on the Chandra observations of Swift J1818.0-1607, which allowed for a high-resolution imaging and spectroscopic study of the magnetar and its environment. The 1-10 keV spectrum of the magnetar is best described by a single blackbody model with a temperature of 1.2pm0.1 keV and an unabsorbed flux of 1.9e-11 ergs/cm^2/s. This implies an X-ray luminosity of ~9.6e34 ergs/s and an efficiency of ~0.13 at a distance of 6.5 kpc. The Chandra image also shows faint diffuse emission out to >10 from the magnetar, with its spectrum adequately described by a powerlaw with a photon index of 2.0pm0.5 and a luminosity of ~8.1e33 ergs/s. The extended emission is likely dominated by a dust scattering halo and future observations of the source in quiescence will reveal any underlying compact wind nebula. We conclude that Swift J1818.0-1607 is a transient source showing properties between high-B pulsars and magnetars, and could be powered at least partly by its high spin-down similar to the rotation-powered pulsars.
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