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Neutron star atmosphere composition: the quiescent, low-mass X-ray binary in the globular cluster M28

Neutron star atmosphere composition: the quiescent, low-mass X-ray binary in the globular cluster M28
Neutron star atmosphere composition: the quiescent, low-mass X-ray binary in the globular cluster M28
Using deep Chandra observations of the globular cluster M28, we study the quiescent X-ray emission of a neutron star in a low-mass X-ray binary in order to constrain the chemical composition of the neutron star atmosphere and the equation of state of dense matter. We fit the spectrum with different neutron star atmosphere models composed of hydrogen, helium or carbon. The parameter values obtained with the carbon model are unphysical and such a model can be ruled out. Hydrogen and helium models give realistic parameter values for a neutron star, and the derived mass and radius are clearly distinct depending on the composition of the atmosphere. The hydrogen model gives masses/radii consistent with the canonical values of 1.4 M_Sun and 10 km, and would allow for the presence of exotic matter inside neutron stars. On the other hand, the helium model provides solutions with higher masses/radii, consistent with the stiffest equations of state. Measurements of neutron star masses/radii by spectral fitting should consider the possibility of heavier element atmospheres, which produce larger masses/radii for the same data, unless the composition of the accretor is known independently.
1365-2966
1556-1561
Servillat, Mathieu
78700dd4-70a4-4a50-afd5-199db816f58a
Heinke, Craig O.
d7382ed2-cb85-4e15-b2d9-296fc8b6221d
Ho, Wynn C. G.
d78d4c52-8f92-4846-876f-e04a8f803a45
Grindlay, Jonathan E.
fd33d733-8c24-43e8-8c97-2432b24949f7
Hong, JaeSub
81fb462e-abdd-475d-ab4a-2eb38122047a
van den Berg, Maureen
e55501cd-64ab-449f-a619-acd8cae10781
Bogdanov, Slavko
39f20582-4d71-4b1a-ae2a-b266367341ef
Servillat, Mathieu
78700dd4-70a4-4a50-afd5-199db816f58a
Heinke, Craig O.
d7382ed2-cb85-4e15-b2d9-296fc8b6221d
Ho, Wynn C. G.
d78d4c52-8f92-4846-876f-e04a8f803a45
Grindlay, Jonathan E.
fd33d733-8c24-43e8-8c97-2432b24949f7
Hong, JaeSub
81fb462e-abdd-475d-ab4a-2eb38122047a
van den Berg, Maureen
e55501cd-64ab-449f-a619-acd8cae10781
Bogdanov, Slavko
39f20582-4d71-4b1a-ae2a-b266367341ef

Servillat, Mathieu, Heinke, Craig O., Ho, Wynn C. G., Grindlay, Jonathan E., Hong, JaeSub, van den Berg, Maureen and Bogdanov, Slavko (2012) Neutron star atmosphere composition: the quiescent, low-mass X-ray binary in the globular cluster M28. Monthly Notices of the Royal Astronomical Society, 423 (2), 1556-1561. (doi:10.1111/j.1365-2966.2012.20976.x).

Record type: Article

Abstract

Using deep Chandra observations of the globular cluster M28, we study the quiescent X-ray emission of a neutron star in a low-mass X-ray binary in order to constrain the chemical composition of the neutron star atmosphere and the equation of state of dense matter. We fit the spectrum with different neutron star atmosphere models composed of hydrogen, helium or carbon. The parameter values obtained with the carbon model are unphysical and such a model can be ruled out. Hydrogen and helium models give realistic parameter values for a neutron star, and the derived mass and radius are clearly distinct depending on the composition of the atmosphere. The hydrogen model gives masses/radii consistent with the canonical values of 1.4 M_Sun and 10 km, and would allow for the presence of exotic matter inside neutron stars. On the other hand, the helium model provides solutions with higher masses/radii, consistent with the stiffest equations of state. Measurements of neutron star masses/radii by spectral fitting should consider the possibility of heavier element atmospheres, which produce larger masses/radii for the same data, unless the composition of the accretor is known independently.

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Published date: 22 March 2012
Organisations: Applied Mathematics

Identifiers

Local EPrints ID: 336374
URI: http://eprints.soton.ac.uk/id/eprint/336374
ISSN: 1365-2966
PURE UUID: 7c1fec8b-a9ba-4d7f-b730-03a2ff5e7150
ORCID for Wynn C. G. Ho: ORCID iD orcid.org/0000-0002-6089-6836

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Date deposited: 22 Mar 2012 16:15
Last modified: 14 Mar 2024 10:42

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Contributors

Author: Mathieu Servillat
Author: Craig O. Heinke
Author: Wynn C. G. Ho ORCID iD
Author: Jonathan E. Grindlay
Author: JaeSub Hong
Author: Maureen van den Berg
Author: Slavko Bogdanov

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