Anomalous X-ray pulsars and soft gamma-ray repeaters in supernova remnants

I consider the state of play regarding associations of supernova remnants (SNRs) with anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs). The three AXP/SNR associations are convincing, and are consistent with AXPs being young, low-velocity neutron stars. The three SGR/SNR associations are far more likely to be chance superpositions, and rely on SGRs being high velocity (>1000 km/s) objects. These results imply either that AXPs evolve into SGRs, or that SGRs and AXPs represent different populations of object.