MG14 - Talk detail |
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Participant |
Ikhsanov, Nazar | |||||||
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Institution |
Saint-Petersburg State University - Universitetskii pr. 28 - Saint Petersburg - - Russia | |||||||
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AC2 |
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Oral abstract |
Title |
Magnetic-levitation accretion by neutron stars | |||||
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Abstract |
Quasi-spherical and Keplerian disk accretion scenarios encounter major difficulties explaining the origin and observed spin evolution of long-period X-ray pulsars. We show that these difficulties reflect an oversimplification of the scenarios in which the magnetic field of the accretion flow is neglected. We find that the accretion picture onto a neutron star which captures material from a magnetized wind differs from those previously suggested. It can be explained in terms of a dense non-Keplerian magnetic disk in which the material is confined by its intrinsic magnetic field. This scenario (a so called Magnetic-Levitation Accretion, MLA) is actively investigated for the case of a black hole for more than 40 years but has been applied to the case of a neutron star only recently. We find that a neutron star accreting material from the magnetically-levitating disk (MAGLEV-disk) brakes harder and the radius of its magnetosphere is significantly smaller than that evaluated in the traditional non-magnetic accretion flow scenarios. We show that the mass-transfer towards the neutron star in MLA scenario is governed by anomalous diffusion and the expected appearance of the MLA pulsar are in a good agreement with observations. |
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Session |
WD2 |
Accepted |
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Oral abstract |
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Why periods of AXPs/SGRs are clustered around 2-12 second? | |||||
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Abstract |
We explore a possibility for AXPs and SGRs to be descendants of high-mass X-ray binaries which have been disintegrated in the second supernova explosion. The spin period of neutron stars in high-mass X-ray binaries evolves towards the equilibrium period, averaging around a few seconds. After the explosion of its massive companion, the neutron star turns out to be embedded into a dense gaseous envelope, the accretion from which leads to the formation of a residual magnetically-levitating disk. We show that the expected mass of the disk, 10^-7 - 10^-8 M_sun, is sufficient to maintain the process of accretion at the rate 10^14 - 10^15 g/s over a time span of a few thousand years. During this period the star manifests itself as an isolated X-ray pulsar with a number of parameters resembling those of AXPs and SGRs. Period clustering of such pulsars can be provided if the lifetime of the residual disk does not exceed the spin-down timescale of the neutron star. References: 1. Bisnovatyi-Kogan and Ikhsanov, Astronomy Reports, 58, 217 (2014) [arXiv:1401.2634v2] 2. Bisnovatyi-Kogan and Ikhsanov, Astronomy Reports, 59, in press (2015) [arXiv:1407.6733v3] |
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Pdf file |
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