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

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.; Soria, R.

doi:10.1093/mnrasl/slz086

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

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.; Soria, R.

Authors

R. Sathyaprakash

Professor Tim Roberts t.p.roberts@durham.ac.uk
Professor

D.J. Walton

F. Fuerst

M. Bachetti

C. Pinto

W.N. Alston

H.P. Earnshaw

A.C. Fabian

M.J. Middleton

R. Soria

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 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.

Citation

Sathyaprakash, R., Roberts, T., Walton, D., Fuerst, F., Bachetti, M., Pinto, C., …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, 488(1), L35-L40. https://doi.org/10.1093/mnrasl/slz086

Journal Article Type	Article
Acceptance Date	May 30, 2019
Online Publication Date	Jul 2, 2019
Publication Date	Sep 30, 2019
Deposit Date	Jun 4, 2019
Publicly Available Date	Jun 11, 2019
Journal	Monthly Notices of the Royal Astronomical Society
Print ISSN	0035-8711
Electronic ISSN	1365-2966
Publisher	Royal Astronomical Society
Peer Reviewed	Peer Reviewed
Volume	488
Issue	1
Pages	L35-L40
DOI	https://doi.org/10.1093/mnrasl/slz086
Related Public URLs	https://arxiv.org/pdf/1906.00640.pdf

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Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.