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

Abstract

We report on a new NuSTAR 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 (kT_BB_1 ∼ 0.5 keV, kT_BB_2 ∼ 1.2 keV) or an absorbed blackbody plus a power law (kT_BB_1 ∼ 0.6 keV, Γ ∼ 3.9). The observed flux was ∼9 × 10<SUP>-12</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP>, ∼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.