Gazing at the ultraslow magnetar in RCW 103 with NuSTAR and Swift

© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. We report on a newNuSTAR observation and on the ongoing Swift X-Ray Telescope monitoring campaign of the peculiar source 1E 161348-5055, located at the centre of the supernova remnant RCW 103, which is recovering from its last outburst in 2016 June. The X-ray spectrum at the epoch of the NuSTAR observation can be described by either two absorbed blackbodies (kTBB1 ~ 0.5 keV, kTBB2 ~ 1.2 keV) or an absorbed blackbody plus a power law (kTBB1 ~ 0.6 keV, Γ ~ 3.9). The observed flux was ~9 × 10-12 erg s-1 cm-2, ~3 times lower than what observed at the outburst onset, but about one order of magnitude higher than the historical quiescent level. A periodic modulation was detected at the known 6.67 h periodicity. The spectral decomposition and evolution along the outburst decay are consistent with 1E 161348-5055 being a magnetar, the slowest ever detected.