Deep searches for X-ray pulsations from Scorpius X-1 and Cygnus X-2 in support of continuous gravitational wave searches

Galaudage, S., Wette, K., Galloway, D. K. and Messenger, C. (2022) Deep searches for X-ray pulsations from Scorpius X-1 and Cygnus X-2 in support of continuous gravitational wave searches. Monthly Notices of the Royal Astronomical Society, 509(2), pp. 1745-1754. (doi: 10.1093/mnras/stab3095)

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Abstract

Neutron stars in low mass X-ray binaries are hypothesised to emit continuous gravitational waves that may be detectable by ground-based observatories. The torque balance model predicts that a higher accretion rate produces larger-amplitude gravitational waves, hence low mass X-ray binaries with high X-ray flux are promising targets for gravitational wave searches. The detection of X-ray pulsations would identify the spin frequency of these neutron stars, and thereby improve the sensitivity of continuous gravitational-wave searches by reducing the volume of the search parameter space. We perform a semi-coherent search for pulsations in the two low mass X-ray binaries Scorpius X-1 and Cygnus X-2 using X-ray data from the Rossi X-ray Timing Explorer Proportional Counter Array. We find no clear evidence for pulsations, and obtain upper limits (at 90 per cent confidence) on the fractional pulse amplitude, with the most stringent being 0.034 per cent for Scorpius X-1 and 0.23 per cent for Cygnus X-2. These upper limits improve upon those in previous work by factors of ∼8.2 and ∼1.6 respectively.

Item Type:Articles
Additional Information:This research was conducted by the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav), through project number CE170100004. The authors also gratefully acknowledge the Science and Technology Facilities Council of the United Kingdom. CM is supported by the Science and Technology Research Council (grant No. ST/L000946/1). This research has made use of data and software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. The searches for X-ray pulsations were performed on the OzSTAR national facility at Swinburne University of Technology. OzSTAR is funded by Swinburne University of Technology and the National Collaborative Research Infrastructure Strategy (NCRIS).
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Messenger, Dr Christopher
Authors: Galaudage, S., Wette, K., Galloway, D. K., and Messenger, C.
College/School:College of Science and Engineering > School of Physics and Astronomy
Research Centre:College of Science and Engineering > School of Physics and Astronomy > Institute for Gravitational Research
Journal Name:Monthly Notices of the Royal Astronomical Society
Publisher:Oxford University Press (OUP)
ISSN:1365-2966
ISSN (Online):1365-2966
Published Online:27 October 2021
Copyright Holders:Copyright © 2021 The Authors
First Published:Monthly Notices of the Royal Astronomical Society 509(2):1745–1754
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
169451Investigations in Gravitational RadiationSheila RowanScience and Technology Facilities Council (STFC)ST/L000946/1P&S - Physics & Astronomy