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A systematic study of soft X-ray pulse profiles of magnetars in quiescence

A systematic study of soft X-ray pulse profiles of magnetars in quiescence
A systematic study of soft X-ray pulse profiles of magnetars in quiescence
Magnetars are neutron stars with extremely high surface magnetic fields. They show diverse X-ray pulse profiles in the quiescent state. We perform a systematic Fourier analysis of their soft X-ray pulse profiles. We find that most magnetars have a single-peaked profile and hence have low amplitudes of the second Fourier harmonic (A2). On the other hand, the pulsed fraction (PF) spreads over a wide range. We compared the results with theoretical profiles assuming various surface hotspot asymmetries, viewing geometries, and beaming functions. We found that a single value of the intensity ratio r between two antipodal hotspots is unable to reproduce the observed distribution of A2 and PF for all magnetars. The inferred r is probably anticorrelated with the thermal luminosity, implying that high-luminosity magnetars tend to have two symmetric hotspots. Our results are consistent with theoretical predictions, for which the existence of an evolving toroidal magnetic field breaks the symmetry of the surface temperature.
0035-8711
4274-4286
Hu, Chin-Ping
38ee07da-9735-4ef2-9662-35d9f0dc747b
Ng, C.-Y.
a7854a32-33ee-44c3-b58d-6654da468894
Ho, Wynn C.G.
d78d4c52-8f92-4846-876f-e04a8f803a45
Hu, Chin-Ping
38ee07da-9735-4ef2-9662-35d9f0dc747b
Ng, C.-Y.
a7854a32-33ee-44c3-b58d-6654da468894
Ho, Wynn C.G.
d78d4c52-8f92-4846-876f-e04a8f803a45

Hu, Chin-Ping, Ng, C.-Y. and Ho, Wynn C.G. (2019) A systematic study of soft X-ray pulse profiles of magnetars in quiescence. Monthly Notices of the Royal Astronomical Society, 485 (3), 4274-4286. (doi:10.1093/mnras/stz513).

Record type: Article

Abstract

Magnetars are neutron stars with extremely high surface magnetic fields. They show diverse X-ray pulse profiles in the quiescent state. We perform a systematic Fourier analysis of their soft X-ray pulse profiles. We find that most magnetars have a single-peaked profile and hence have low amplitudes of the second Fourier harmonic (A2). On the other hand, the pulsed fraction (PF) spreads over a wide range. We compared the results with theoretical profiles assuming various surface hotspot asymmetries, viewing geometries, and beaming functions. We found that a single value of the intensity ratio r between two antipodal hotspots is unable to reproduce the observed distribution of A2 and PF for all magnetars. The inferred r is probably anticorrelated with the thermal luminosity, implying that high-luminosity magnetars tend to have two symmetric hotspots. Our results are consistent with theoretical predictions, for which the existence of an evolving toroidal magnetic field breaks the symmetry of the surface temperature.

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1903.01091 - Accepted Manuscript
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Accepted/In Press date: 18 February 2019
Published date: 27 March 2019

Identifiers

Local EPrints ID: 429209
URI: https://eprints.soton.ac.uk/id/eprint/429209
ISSN: 0035-8711
PURE UUID: d2ec6901-0020-4765-9743-ba00de250ed8
ORCID for Wynn C.G. Ho: ORCID iD orcid.org/0000-0002-6089-6836

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Date deposited: 22 Mar 2019 17:30
Last modified: 19 Apr 2019 04:01

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