The Proper Motion, Age, and Initial Spin Period of PSR J0538+2817 in S147

We present results of timing observations of the 143-ms pulsar J0538+2817 that provide a proper motion measurement which clearly associates the pulsar with the supernova remnant S147. We measure a proper motion of 67₋₂₂⁺⁴⁸ mas yr⁻¹, implying a transverse velocity of v= 385⁺²⁶⁰₋₁₃₀ km s⁻¹. We derive an age of the pulsar and S147 of only $30pm4$ kyr which is a factor of 20 times less than the pulsar's characteristic age of tauc = 620 kyr. This age implies an initial spin period of P₀=139 ms, close to the present pulse period and a factor of several larger than what is usually inferred for birth periods. Implications for recent X-ray detections of this pulsar are discussed.