Period clustering of anomalous X-ray pulsars |
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| Authors: | Email author" target="_blank">G?S?Bisnovatyi-KoganEmail author N?R?Ikhsanov |
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| Institution: | 1.Space Research Institute,Russian Academy of Sciences,Moscow,Russia;2.MEPhI National Research Nuclear University,Moscow,Russia;3.Central (Pulkovo) Astronomical Observatory,Russian Academy of Sciences,St. Petersburg,Russia;4.Saint Petersburg State University,Starii Peterhof, St. Petersburg,Russia |
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| Abstract: | The question of why the observed periods of anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) cluster in the range 2–12 s is discussed. The possibility that AXPs and SGRs are the descendants of high-mass X-ray binaries that have disintegrated in core-collapse supernova explosions is investigated. The spin periods of neutron stars in high-mass X-ray binaries evolve towards the equilibrium period, which is a few seconds, on average. After the explosion of its massive companion, the neutron star becomes embedded in a dense gaseous envelope, and accretion from this envelope leads to the formation of a residual magnetically levitating disk. It is shown that the expected mass of the disk in this case is 10?7–10?8 M⊙, which is sufficient to support accretion at the rate 1014–1015 g/s over a few thousand years. During this period, the star manifests itself as an isolated X-ray pulsar with a number of parameters similar to those of AXPs and SGRs. The periods of such pulsars can cluster if the lifetime of the residual disk does not exceed the spin-down timescale of the neutron star. |
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