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The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2

The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2
The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2

We report the detection of weak pulsations from the archetypal ultraluminous X-ray source (ULX) NGC 1313 X-2. Acceleration searches reveal sinusoidal pulsations in segments of two out of six new deep observations of this object, with a period of ∼1.5 s and a pulsed fraction of ∼ 5\ \rm per\ cent. We use Monte Carlo simulations to demonstrate that the individual detections are unlikely to originate in false Poisson noise detections given their very close frequencies; their strong similarity to other pulsations detected from ULXs also argues they are real. The presence of a large bubble nebula surrounding NGC 1313 X-2 implies an age of order 1 Myr for the accreting phase of the ULX, which implies that the neutron star's (NS) magnetic field has not been suppressed over time by accreted material, nor has the NS collapsed into a black hole, despite an average energy output into the nebula two orders of magnitude above Eddington. This argues that most of the accreted material has been expelled over the lifetime of the ULX, favouring physical models including strong winds and/or jets for NS ULXs.

accretion, accretion discs, X-rays: binaries
1745-3925
L35-L40
Sathyaprakash, R.
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Roberts, T. P.
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Walton, D. J.
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Fuerst, F.
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Bachetti, M.
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Pinto, C.
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Alston, W. N.
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Earnshaw, H. P.
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Fabian, A. C.
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Middleton, M.J.
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Soria, R.
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Sathyaprakash, R.
f0109fb1-9103-423d-87bd-9331f62a6989
Roberts, T. P.
4a31f81a-507d-45ea-ada9-ee3aa21ebb7d
Walton, D. J.
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Fuerst, F.
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Bachetti, M.
fb499a38-fcff-4761-b0ad-8f03fd25dd5d
Pinto, C.
b63ebc6f-8e4f-4e59-a553-f26f60d076f6
Alston, W. N.
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Earnshaw, H. P.
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Fabian, A. C.
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Middleton, M.J.
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Soria, R.
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Sathyaprakash, R., Roberts, T. P., Walton, D. J., Fuerst, F., Bachetti, M., Pinto, C., Alston, W. N., Earnshaw, H. P., Fabian, A. C., Middleton, M.J. and Soria, R. (2019) The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2. Monthly Notices of the Royal Astronomical Society: Letters, 488 (1), L35-L40. (doi:10.1093/mnrasl/slz086).

Record type: Article

Abstract

We report the detection of weak pulsations from the archetypal ultraluminous X-ray source (ULX) NGC 1313 X-2. Acceleration searches reveal sinusoidal pulsations in segments of two out of six new deep observations of this object, with a period of ∼1.5 s and a pulsed fraction of ∼ 5\ \rm per\ cent. We use Monte Carlo simulations to demonstrate that the individual detections are unlikely to originate in false Poisson noise detections given their very close frequencies; their strong similarity to other pulsations detected from ULXs also argues they are real. The presence of a large bubble nebula surrounding NGC 1313 X-2 implies an age of order 1 Myr for the accreting phase of the ULX, which implies that the neutron star's (NS) magnetic field has not been suppressed over time by accreted material, nor has the NS collapsed into a black hole, despite an average energy output into the nebula two orders of magnitude above Eddington. This argues that most of the accreted material has been expelled over the lifetime of the ULX, favouring physical models including strong winds and/or jets for NS ULXs.

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The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2 - Accepted Manuscript
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Accepted/In Press date: 22 May 2019
Published date: 1 July 2019
Additional Information: arXiv is AM
Keywords: accretion, accretion discs, X-rays: binaries

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Local EPrints ID: 433076
URI: http://eprints.soton.ac.uk/id/eprint/433076
ISSN: 1745-3925
PURE UUID: 9f07d7a3-0aac-44b6-a76e-f0c0ae7fc27e

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Date deposited: 07 Aug 2019 16:30
Last modified: 09 Oct 2020 16:37

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Contributors

Author: R. Sathyaprakash
Author: T. P. Roberts
Author: D. J. Walton
Author: F. Fuerst
Author: M. Bachetti
Author: C. Pinto
Author: W. N. Alston
Author: H. P. Earnshaw
Author: A. C. Fabian
Author: M.J. Middleton
Author: R. Soria

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