Ejector and propeller spin - down : How might a superluminous supernova millisecond magnetar become the 6 . 67 hr pulsar in RCW 103

The X-ray source 1E 161348−5055 in the supernova remnant RCW 103 recently exhibited X-ray activity typical of magnetars, i.e. neutron stars with magnetic fields & 1014 − 1015 G. However, 1E 161348−5055 has an observed period of 6.67 hr, in contrast to magnetars which have a spin period of seconds. Here we describe a simple model which can explain the spin evolution of 1E 161348−5055, as well as other magnetars, from an initial period of milliseconds that would be required for dynamo generation of magnetar-strength magnetic fields. We propose that the key difference between 1E 161348−5055 and other magnetars is the persistence of a remnant disk of small total mass. This disk caused 1E 161348−5055 to undergo ejector and propeller phases in its life, during which strong torques caused a rapid increase of its spin period. By matching its observed spin period and ≈ 1 − 3 kyr age, we find that 1E 161348−5055 has the (slightly) highest magnetic field of all known magnetars, with B ∼ 5 × 1015 G, and that its disk had a mass of ∼ 1024 g, comparable to that of the asteroid Ceres.