Implications of the Narrow Period Distribution of Anomalous X-ray Pulsars and Soft Gamma-Ray Repeaters

Abstract

The spin periods of the ten observed Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters lie in the very narrow range 6-12 s. We use a point likelihood technique to assess the constraints this clustering imposes on the birth period and on the final period of such systems. We consider a general law for their spin evolution described by a constant braking index. We find that, for positive values of the braking index, the observed clustering requires an upper cut-off period that is very close to the maximum observed period of about 12 s. We also show that the constraint on the birth period depends very strongly on the assumed value of the braking index n, ranging from a few milliseconds for n>2 to a few seconds for n<2. We discuss the possible ways of tightening these constraints based on similarities with the population of radio pulsars and with future observations of such sources with current X-ray observatories.

Submitted to ApJ Letters

References in corpus (3)

• An Optical Counterpart to the Anomalous X-ray Pulsar 4U 0142+61
• Surface Emission Properties of Strongly Magnetic Neutron Stars
• Constraints on Thermal Emission Models of Anomalous X-ray Pulsars

Cited by in corpus (12)

• The strongest cosmic magnets: Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars
• 1E 1547.0-5408: a radio-emitting magnetar with a rotation period of 2 seconds
• A highly resistive layer within the crust of X-ray pulsars limits their spin periods
• Anomalous X-ray pulsars: Persistent States with Fallback Disks
• On the evolution of anomalous X-ray pulsars and soft gamma ray repeaters with fallback disks
• Can Thin Disks Produce Anomalous X-Ray Pulsars?
• Electrodynamics of Magnetars III: Pair Creation Processes in an Ultrastrong Magnetic Field and Particle Heating in a Dynamic Magnetosphere
• The Anomalous X-Ray Pulsar 4U 0142+61: A Neutron Star with a Gaseous Fallback Disk
• Magnetic Field Decay and Period Evolution of Anomalous X-Ray Pulsars in the Context of Quark Stars
• Spinning-Down of Moving Magnetars in the Propeller Regime
• Subsonic propellers in a strong wind as anomalous X-ray pulsars
• Thin Disk Models of Anomalous X-ray Pulsars