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Lense-Thirring precession in ULXs as a possible means to constrain the neutron star equation of state

Lense-Thirring precession in ULXs as a possible means to constrain the neutron star equation of state
Lense-Thirring precession in ULXs as a possible means to constrain the neutron star equation of state
The presence of neutron stars in at least three ultraluminous X-ray sources is now firmly established and offers an unambiguous view of super-critical accretion. All three systems show long-time-scale periods (60-80 d) in the X-rays and/or optical, two of which are known to be super-orbital in nature. Should the flow be classically super critical, i.e. the Eddington limit is reached locally in the disc (implying surface dipole fields that are sub-magnetar in strength), then the large scale-height flow can precess through the Lense-Thirring effect which could provide an explanation for the observed super-orbital periods. By connecting the details of the Lense-Thirring effect with the observed pulsar spin period, we are able to infer the moment of inertia and therefore equation of state of the neutron star without relying on the inclination of or distance to the system. We apply our technique to the case of NGC 7793 P13 and demonstrate that stronger magnetic fields imply stiffer equations of state. We discuss the caveats and uncertainties, many of which can be addressed through forthcoming radiative magnetohydrodynamic (RMHD) simulations and their connection to observation.
0035-8711
154-166
Middleton, M.J.
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Fragile, P.C.
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Bachetti, M.
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Brightman, M.
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Jiang, Y-F
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Ho, W.C.G.
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Roberts, T.P.
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Ingram, A.R.
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Dauser, T.
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Pinto, C.
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Walton, D.J.
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Fuerst, F.
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Fabian, A.C.
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Gehrels, N.
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Middleton, M.J.
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Fragile, P.C.
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Bachetti, M.
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Brightman, M.
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Jiang, Y-F
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Ho, W.C.G.
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Roberts, T.P.
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Ingram, A.R.
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Dauser, T.
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Pinto, C.
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Walton, D.J.
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Fuerst, F.
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Fabian, A.C.
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Gehrels, N.
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Middleton, M.J., Fragile, P.C., Bachetti, M., Brightman, M., Jiang, Y-F, Ho, W.C.G., Roberts, T.P., Ingram, A.R., Dauser, T., Pinto, C., Walton, D.J., Fuerst, F., Fabian, A.C. and Gehrels, N. (2018) Lense-Thirring precession in ULXs as a possible means to constrain the neutron star equation of state Monthly Notices of the Royal Astronomical Society, 475, (1), pp. 154-166. (doi:10.1093/mnras/stx2986).

Record type: Article

Abstract

The presence of neutron stars in at least three ultraluminous X-ray sources is now firmly established and offers an unambiguous view of super-critical accretion. All three systems show long-time-scale periods (60-80 d) in the X-rays and/or optical, two of which are known to be super-orbital in nature. Should the flow be classically super critical, i.e. the Eddington limit is reached locally in the disc (implying surface dipole fields that are sub-magnetar in strength), then the large scale-height flow can precess through the Lense-Thirring effect which could provide an explanation for the observed super-orbital periods. By connecting the details of the Lense-Thirring effect with the observed pulsar spin period, we are able to infer the moment of inertia and therefore equation of state of the neutron star without relying on the inclination of or distance to the system. We apply our technique to the case of NGC 7793 P13 and demonstrate that stronger magnetic fields imply stiffer equations of state. We discuss the caveats and uncertainties, many of which can be addressed through forthcoming radiative magnetohydrodynamic (RMHD) simulations and their connection to observation.

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Accepted/In Press date: 17 November 2017
e-pub ahead of print date: 23 November 2017
Published date: 1 March 2018

Identifiers

Local EPrints ID: 417343
URI: https://eprints.soton.ac.uk/id/eprint/417343
ISSN: 0035-8711
PURE UUID: 909bd692-e1df-445d-a416-4ad7bc4ee7f5
ORCID for W.C.G. Ho: ORCID iD orcid.org/0000-0002-6089-6836

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Date deposited: 30 Jan 2018 17:30
Last modified: 19 Feb 2018 17:31

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Contributors

Author: M.J. Middleton
Author: P.C. Fragile
Author: M. Bachetti
Author: M. Brightman
Author: Y-F Jiang
Author: W.C.G. Ho ORCID iD
Author: T.P. Roberts
Author: A.R. Ingram
Author: T. Dauser
Author: C. Pinto
Author: D.J. Walton
Author: F. Fuerst
Author: A.C. Fabian
Author: N. Gehrels

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