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Magnetic field strength of a neutron-star-powered ultraluminous X-ray source

Magnetic field strength of a neutron-star-powered ultraluminous X-ray source
Magnetic field strength of a neutron-star-powered ultraluminous X-ray source

Ultraluminous X-ray sources (ULXs) are bright X-ray sources in nearby galaxies not associated with the central supermassive black hole. Their luminosities imply they are powered by either an extreme accretion rate onto a compact stellar remnant, or an intermediate mass (~100-105 M ) black hole 1 . Recently detected coherent pulsations coming from three bright ULXs 2-5 demonstrate that some of these sources are powered by accretion onto a neutron star, implying accretion rates significantly in excess of the Eddington limit, a high degree of geometric beaming, or both. The physical challenges associated with the high implied accretion rates can be mitigated if the neutron star surface field is very high (1014 G) 6, since this suppresses the electron scattering cross-section, reducing the radiation pressure that chokes off accretion for high luminosities. Surface magnetic field strengths can be determined through cyclotron resonance scattering features 7,8 produced by the transition of charged particles between quantized Landau levels. Here, we present the detection at a significance of 3.8σ of an absorption line at 4.5 keV in the Chandra spectrum of a ULX in M51. This feature is likely to be a cyclotron resonance scattering feature produced by the strong magnetic field of a neutron star. Assuming scattering off electrons, the magnetic field strength is implied to be ~1011 G, while protons would imply a magnetic field of B ~ 1015 G.

2397-3366
312-316
Brightman, M.
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Harrison, F.A.
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Fürst, F.
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Middleton, M.J.
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Walton, D.J.
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Stern, D.
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Fabian, A.C.
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Heida, M.
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Barret, D.
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Bachetti, M.
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Brightman, M.
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Harrison, F.A.
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Fürst, F.
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Middleton, M.J.
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Walton, D.J.
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Stern, D.
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Fabian, A.C.
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Heida, M.
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Barret, D.
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Bachetti, M.
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Brightman, M., Harrison, F.A., Fürst, F., Middleton, M.J., Walton, D.J., Stern, D., Fabian, A.C., Heida, M., Barret, D. and Bachetti, M. (2018) Magnetic field strength of a neutron-star-powered ultraluminous X-ray source. Nature Astronomy, 2 (4), 312-316. (doi:10.1038/s41550-018-0391-6).

Record type: Article

Abstract

Ultraluminous X-ray sources (ULXs) are bright X-ray sources in nearby galaxies not associated with the central supermassive black hole. Their luminosities imply they are powered by either an extreme accretion rate onto a compact stellar remnant, or an intermediate mass (~100-105 M ) black hole 1 . Recently detected coherent pulsations coming from three bright ULXs 2-5 demonstrate that some of these sources are powered by accretion onto a neutron star, implying accretion rates significantly in excess of the Eddington limit, a high degree of geometric beaming, or both. The physical challenges associated with the high implied accretion rates can be mitigated if the neutron star surface field is very high (1014 G) 6, since this suppresses the electron scattering cross-section, reducing the radiation pressure that chokes off accretion for high luminosities. Surface magnetic field strengths can be determined through cyclotron resonance scattering features 7,8 produced by the transition of charged particles between quantized Landau levels. Here, we present the detection at a significance of 3.8σ of an absorption line at 4.5 keV in the Chandra spectrum of a ULX in M51. This feature is likely to be a cyclotron resonance scattering feature produced by the strong magnetic field of a neutron star. Assuming scattering off electrons, the magnetic field strength is implied to be ~1011 G, while protons would imply a magnetic field of B ~ 1015 G.

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Magnetic field strength of a neutron-star-powered ultraluminous X-ray source - Accepted Manuscript
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Accepted/In Press date: 16 January 2018
e-pub ahead of print date: 26 February 2018
Published date: 1 April 2018

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Local EPrints ID: 420377
URI: http://eprints.soton.ac.uk/id/eprint/420377
ISSN: 2397-3366
PURE UUID: a69dedb2-bbd1-49ba-bc51-4fe9a0b2ff07

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Date deposited: 04 May 2018 16:30
Last modified: 17 Dec 2019 05:28

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Contributors

Author: M. Brightman
Author: F.A. Harrison
Author: F. Fürst
Author: M.J. Middleton
Author: D.J. Walton
Author: D. Stern
Author: A.C. Fabian
Author: M. Heida
Author: D. Barret
Author: M. Bachetti

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