Inferring initial spin periods for neutron stars in composite remnants

We propose a method to infer the initial spin periods of pulsars residing in composite supernova remnants. Such a remnant consists of both a plerionic and a shell-type component, corresponding to the pulsar wind nebula driven by the spin-down luminosity of the central pulsar and the blast wave bounding the supernova remnant, respectively. Theoretical investigations including hydrodynamical simulations have shown that, at late times (similar to 1000-10,000 yr), a simple scaling law connects the radius of the supernova shell to the radius of the plerion. The energy content of the plerion and the total mechanical energy of the supernova remnant enter into this scaling law. One can use this scaling law to estimate the initial spin periods of pulsars residing in composite remnants. We discuss potential pitfalls of this method, including the effect of a small remnant age and of strong radiative losses in the plerion.