2011MNRAS.418..170E

The X-ray source 1E 161348-5055 lies at the centre of the 2-kyr-old supernova remnant RCW 103. Owing to its 24-ks modulation, orders-of-magnitude flux variability over a few months/years and lack of an obvious optical counterpart, 1E 161348-5055 defies assignment to any known class of X-ray sources. Starting from 2006 April, Swift observed 1E 161348-5055 with its X-Ray Telescope for ∼ 2 ks approximately once per month. During the five years covered, the source has remained in a quiescent state, with an average observed flux of ∼ 1.7 {x} 10^–12 erg/cm2/s (1–10 keV), ∼ 20 times lower than the historical maximum attained in its 1999–2000 outburst. The long time-span of the Swift data allows us to obtain an accurate measure of the period of 1E 161348-5055 [P= 24 030.42(2) s] and to derive the first upper limit on its period derivative (|{dot}P| < 1.6 x 10^–9 s/s at 3σ).