2020ApJ...904L..19B

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 ∼ 2.5 x 10¹⁴ G, spin-down luminosity {dot}E ∼ 7.2 x 10³⁵ erg s^–1, and characteristic age τ_c ∼ 470 yr. 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 1.2 ± 0.1 keV and an unabsorbed flux of 1.9_–0.3^+0.4 x 10^–11 erg cm^–2 s^–1. This implies an X-ray luminosity of 9.6_–1.5^+2.0x10³⁴ d_6.5² erg s^–1 and efficiency of L_X/{dot}E ∼ 0.13 d_6.5² 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 power law with a photon index of 2.0 ± 0.5 and a luminosity of ∼8.1 x 10³³ d_6.5² erg s^–1. 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 rotation-powered pulsars.