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Super-Eddington accretion on to a magnetized neutron star
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. University of Turku, Finland.
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. University of Turku, Finland.
2017 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 470, no 3, p. 2799-2813Article in journal (Refereed) Published
Abstract [en]

Most of ultraluminous X-ray sources are thought to be objects accreting above their Eddington limits. In the recently identified class of ultraluminous X-ray pulsars, accretor is a neutron star and thus has a fairly small mass with a small Eddington limit. The accretion disc structure around such an object affects important observables such as equilibrium period, period derivative and the size of the magnetosphere. We propose a model of a nearly standard accretion disc interacting with the magnetosphere only in a thin layer near the inner disc rim. Our calculations show that the size of the magnetosphere may be represented as the classical Alfven radius times a dimensionless factor. which depends only on the disc thickness. In the case of radiation-pressure-dominated disc, the size of the magnetosphere does not depend on the mass accretion rate. In general, increasing the disc thickness leads to a larger magnetosphere size in units of the Alfven radius. For large enough mass accretion rates and magnetic moments, it is important to take into account not only the pressure of the magnetic field and the radiation pressure inside the disc, but also the pressure of the radiation produced close to the surface of the neutron star in accretion column. The magnetospheric size may increase by up to factor of 2 as a result of the effects related to the disc thickness and the irradiation from the central source. Accounting for these effects reduces the estimate of the neutron star magnetic moment by a factor of several orders.

Place, publisher, year, edition, pages
Oxford University Press, 2017. Vol. 470, no 3, p. 2799-2813
Keyword [en]
accretion, accretion discs, hydrodynamics, magnetic fields, stars: neutron, X-rays: binaries
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-212593DOI: 10.1093/mnras/stx1372ISI: 000406844800020Scopus ID: 2-s2.0-85023746330OAI: oai:DiVA.org:kth-212593DiVA, id: diva2:1136069
Note

QC 20170825

Available from: 2017-08-25 Created: 2017-08-25 Last updated: 2017-08-25Bibliographically approved

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