Inferring Initial Spin Periods for Neutron Stars in Composite Remnants

We propose a method to infer the initial spin period of pulsars residing incomposite supernova remnants. Such a remnant consists of both a plerionic and ashell type component, corresponding respectively to the pulsar wind nebuladriven by the spindown luminosity of the central pulsar, and the blastwavebounding the supernova remnant. Theoretical investigations includinghydrodynamical simulations have shown that at late times (~ 1,000 - 10,000years), a simple scaling law connects the radius of the supernova shell to theradius of the plerion. The energy content of the plerion and the totalmechanical energy of the supernova remnant enter into this scaling law. One canuse this scaling law to estimate the initial spin period of pulsars residing incomposite remnants. We discuss potential pitfalls of this method, including theeffect of a small remnant age and of strong radiative losses in the plerion.Comment: 4 pages, 2 figures, accepted by ApJ