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Hunt for Pulsating Ultraluminous X-ray Sources

Song, X. and Walton, D. J. and Lansbury, G. B. and Evans, P. A. and Fabian, A. C. and Earnshaw, H. and Roberts, T. P. (2020) Hunt for Pulsating Ultraluminous X-ray Sources. Monthly Notices of the Royal Astronomical Society, 491 (1). pp. 1260-1277. ISSN 0035-8711.

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Motivated by the recent discoveries that six ultraluminous X-ray sources (ULXs) are powered by highly super-Eddington X-ray pulsars, we searched for additional pulsating ULX (PULX) candidates by identifying sources that exhibit long-term flux variability of at least an order of magnitude (a common feature seen in the six known PULXs, which may potentially be related to transitions to the propeller regime). Expanding on previous studies, we used the available fluxes from XMM–Newton, Swift, and Chandra, along with carefully computed upper limits in cases of a non-detection, to construct long-term light curves for a sample of 296 ULXs selected from the XMM–Newton archive. Among these 296, we find 25 sources showing flux variability larger than a factor of 10, of which 17 show some evidence for (or are at least consistent with) exhibiting bimodal flux distributions, as would be expected for sources undergoing propeller transitions. These sources are excellent candidates for continued monitoring programs to further test for this behaviour. There are three sources in our final sample with fluxes similar to NGC 5907 ULX1, currently the faintest known PULX, which would also be good targets for deeper observations with current facilities to search for pulsations. For the rest of the PULX candidates identified here, the next generation of X-ray telescopes (such as Athena) may be required to determine their nature owing to their lower peak fluxes.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Song, X.0000-0003-4924-0550
Walton, D. J.0000-0001-5819-3552
Lansbury, G. B.0000-0002-5328-9827
Evans, P. A.0000-0002-8465-3353
Fabian, A. C.0000-0002-9378-4072
Earnshaw, H.0000-0001-5857-5622
Roberts, T. P.0000-0001-8252-6337
Additional Information:© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2019 October 24. Received 2019 October 20; in original form 2019 September 2. Published: 31 October 2019. XS thanks the further support of the IoA Summer School Programme. DJW acknowledges financial support from STFC in the form of an Ernest Rutherford Fellowship. PAE acknowledges UKSA support. This research has made use of data obtained from the Chandra Source Catalog, provided by the Chandra X-ray Center (CXC) as part of the Chandra Data Archive.
Funding AgencyGrant Number
University of CambridgeUNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
United Kingdom Space Agency (UKSA)UNSPECIFIED
Subject Keywords:stars: neutron – X-rays: binaries
Issue or Number:1
Record Number:CaltechAUTHORS:20200220-144523449
Persistent URL:
Official Citation:X Song, D J Walton, G B Lansbury, P A Evans, A C Fabian, H Earnshaw, T P Roberts, The hunt for pulsating ultraluminous X-ray sources, Monthly Notices of the Royal Astronomical Society, Volume 491, Issue 1, January 2020, Pages 1260–1277,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101433
Deposited By: Tony Diaz
Deposited On:20 Feb 2020 22:54
Last Modified:20 Feb 2020 22:54

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