Defining Millisecond Pulsars

Millisecond pulsars (MSP) are an important subclass of rotation powered pulsars (RPP), traditionally defined as those with $P_s<20-30$~ms and $B_s\lesssim {10}^{10}$~G. We re-examine this definition by applying Gaussian mixture model (GMM) analysis to identify distinct clusters within the RPP population and find that the MSPs appear to be better demarcated by the condition ${\mathbf{P}}_{\mathbf{s}}\lesssim \mathbf{16}$~ms.