Superburst oscillations: ocean and crustal modes excited by carbon-triggered type I X-ray bursts
Superburst oscillations: ocean and crustal modes excited by carbon-triggered type I X-ray bursts
Accreting neutron stars (NS) can exhibit high frequency modulations in their light curves during thermonuclear X-ray bursts, known as burst oscillations. The frequencies can be offset from the spin frequency of the NS by several Hz, and can drift by 1-3 Hz. One possible explanation is a mode in the bursting ocean, the frequency of which would decrease (in the rotating frame) as the burst cools, hence explaining the drifts. Most burst oscillations have been observed during the H/He-triggered bursts; however there has been one observation of oscillations during a superburst; hours long Type I X-ray bursts caused by unstable carbon burning deeper in the ocean. This paper calculates the frequency evolution of an oceanic r mode during a superburst. The rotating frame frequency varies during the burst from 4-14 Hz and is sensitive to the background parameters, in particular the temperature of the ocean and ignition depth. This calculation is compared to the superburst oscillations observed on 4U-1636-536. The predicted mode frequencies (~10 Hz) would require a spin frequency of ~592 Hz to match observations; 6 Hz higher than the spin inferred from an oceanic r-mode model for the H/He-triggered burst oscillations. This model also overpredicts the frequency drift during the superburst by 90 per cent.
Stars: Neutron, Stars: Oscillations, X-rays: Binaries, X-rays: Bursts
4391-4402
Chambers, F.R.N.
35d0dfb2-0e31-45a5-93a8-0417937b522d
Watts, A.L.
8c906b14-9fb9-4f04-9cb3-2aabd6561162
Cavecchi, Y.
939cba7d-c099-4d5a-a962-1fee916ea176
Garcia, F.
22f7c9f7-815d-449e-ac82-f5fcb8c107c7
Keek, L.
9dcd2383-8c45-4f7c-9d3f-fae8c29385f7
11 July 2018
Chambers, F.R.N.
35d0dfb2-0e31-45a5-93a8-0417937b522d
Watts, A.L.
8c906b14-9fb9-4f04-9cb3-2aabd6561162
Cavecchi, Y.
939cba7d-c099-4d5a-a962-1fee916ea176
Garcia, F.
22f7c9f7-815d-449e-ac82-f5fcb8c107c7
Keek, L.
9dcd2383-8c45-4f7c-9d3f-fae8c29385f7
Chambers, F.R.N., Watts, A.L., Cavecchi, Y., Garcia, F. and Keek, L.
(2018)
Superburst oscillations: ocean and crustal modes excited by carbon-triggered type I X-ray bursts.
Monthly Notices of the Royal Astronomical Society, 477 (4), .
(doi:10.1093/mnras/sty895).
Abstract
Accreting neutron stars (NS) can exhibit high frequency modulations in their light curves during thermonuclear X-ray bursts, known as burst oscillations. The frequencies can be offset from the spin frequency of the NS by several Hz, and can drift by 1-3 Hz. One possible explanation is a mode in the bursting ocean, the frequency of which would decrease (in the rotating frame) as the burst cools, hence explaining the drifts. Most burst oscillations have been observed during the H/He-triggered bursts; however there has been one observation of oscillations during a superburst; hours long Type I X-ray bursts caused by unstable carbon burning deeper in the ocean. This paper calculates the frequency evolution of an oceanic r mode during a superburst. The rotating frame frequency varies during the burst from 4-14 Hz and is sensitive to the background parameters, in particular the temperature of the ocean and ignition depth. This calculation is compared to the superburst oscillations observed on 4U-1636-536. The predicted mode frequencies (~10 Hz) would require a spin frequency of ~592 Hz to match observations; 6 Hz higher than the spin inferred from an oceanic r-mode model for the H/He-triggered burst oscillations. This model also overpredicts the frequency drift during the superburst by 90 per cent.
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Superburst
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sty895
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Accepted/In Press date: 4 April 2018
e-pub ahead of print date: 10 April 2018
Published date: 11 July 2018
Additional Information:
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Keywords:
Stars: Neutron, Stars: Oscillations, X-rays: Binaries, X-rays: Bursts
Identifiers
Local EPrints ID: 422408
URI: http://eprints.soton.ac.uk/id/eprint/422408
ISSN: 1365-2966
PURE UUID: 234dae2b-d87c-4d61-a754-081ffa7a6845
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Date deposited: 23 Jul 2018 16:30
Last modified: 15 Mar 2024 20:20
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Author:
F.R.N. Chambers
Author:
A.L. Watts
Author:
Y. Cavecchi
Author:
F. Garcia
Author:
L. Keek
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