Anomalous X-ray pulsars and soft gamma-ray repeaters – the connection with supernova remnants

Abstract

Many of the properties of anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are still a matter of much debate, as is the connection (if any) between these two groups of sources. In cases where we can identify the supernova remnant (SNR) associated with an AXP or SGR, the extra information thus obtained can provide important constraints as to the nature of these exotic objects. In this paper, I explain the criteria by which an association between a SNR and an AXP/SGR should be judged, review the set of associations which result, and discuss the implications provided by these associations for the ages, environments and evolutionary pathways of the AXPs and SGRs. There are several convincing associations between AXPs and SNRs, demonstrating that AXPs are young neutron stars with moderate space velocities. The lack of associations between SGRs and SNRs implies that the SGRs either represent an older population of neutron stars than do the AXPs, or originate from more massive progenitors.