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.

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