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Diamagnetic screening of the magnetic field in accreting neutron stars – II. The effect of polar cap widening

Konar, Sushan and Choudhuri, AR (2004) Diamagnetic screening of the magnetic field in accreting neutron stars – II. The effect of polar cap widening. In: Monthly Notices of the Royal Astronomical Society, 348 (2). pp. 661-668.

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Recently, we have proposed a model for the screening of the magnetic field of an accreting neutron star by the accreted material flowing from the polar regions towards the equator and sinking there underneath the surface. In this earlier model, it was assumed that the flow pattern remained stationary over time. However, as the surface magnetic field weakens, the accretion takes place over a wider region around the pole, making the flow more radial and isotropic. In the present work, we extend this two-dimensional model to include the time dependence of the flow of the accreted material. The final radial flow is found to be less efficient in screening the magnetic field compared with the initial tangential flow. After an initial phase of rapid decay, the magnetic field slowly reaches an asymptotic value when the accretion becomes nearly isotropic and radial. Assuming the initial extent of the polar cap to be similar to5degrees-10degrees, a simple geometric argument suggests that the magnetic field should decay by 3-4 orders of magnitude before stabilizing to an asymptotic value, consistent with the magnetic fields observed in millisecond pulsars.

Item Type: Journal Article
Publication: Monthly Notices of the Royal Astronomical Society
Publisher: Blackwell Publishing
Additional Information: Copyright of this article belongs to Blackwell Publishing.
Keywords: Binaries: general – stars:magnetic fields – stars:neutron – pulsars:General.
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 18 Dec 2008 11:11
Last Modified: 19 Sep 2010 04:53
URI: http://eprints.iisc.ac.in/id/eprint/16821

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