Searching for propeller-phase ULXs in the XMM–Newton Serendipitous Source Catalogue
Abstract
We search for transient sources in a sample of ultraluminous X-ray sources (ULXs) from the 3XMM-DR4 release of the XMM–Newton Serendipitous Source Catalogue in order to find candidate neutron star ULXs alternating between an accreting state and the propeller regime, in which the luminosity drops dramatically. By examining their fluxes and flux upper limits, we identify five ULXs that demonstrate long-term variability of over an order of magnitude. Using Chandra and Swift data to further characterize their light curves, we find that two of these sources are detected only once and could be X-ray binaries in outburst that only briefly reach ULX luminosities. Two others are consistent with being super-Eddington accreting sources with high levels of inter-observation variability. One source, M51 ULX-4, demonstrates apparent bimodal flux behaviour that could indicate the propeller regime. It has a hard X-ray spectrum, but no significant pulsations in its timing data, although with an upper limit of 10 per cent of the signal pulsed at ∼1.5 Hz a pulsating ULX cannot be excluded, particularly if the pulsations are transient. By simulating XMM–Newton observations of a population of pulsating ULXs, we predict that there could be approximately 200 other bimodal ULXs that have not been observed sufficiently well by XMM–Newton to be identified as transient.
Additional Information
© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2018 February 20. Received 2018 February 20; in original form 2017 December 7. Published: 23 February 2018. We thank the anonymous referee for helpful comments that improved this paper. We gratefully acknowledge support from the Science and Technology Facilities Council (HPE through grant ST/K501979/1, SR through ST/N50404X/1, TPR through ST/P000541/1). HPE acknowledges support under NASA contract NNG08FD60C. This research made use of data obtained from the 3XMM XMM–Newton Serendipitous Source Catalogue, based on archival observations with XMM–Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. We also acknowledge the use of public data obtained from the Chandra Data Archive and the Swift Data Archive.Attached Files
Published - sty501.pdf
Accepted Version - 1802.07753.pdf
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Additional details
- Eprint ID
- 86431
- Resolver ID
- CaltechAUTHORS:20180516-154831076
- ST/K501979/1
- Science and Technology Facilities Council (STFC)
- ST/N50404X/1
- Science and Technology Facilities Council (STFC)
- ST/P000541/1
- Science and Technology Facilities Council (STFC)
- NNG08FD60C
- NASA
- Created
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2018-05-18Created from EPrint's datestamp field
- Updated
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2021-11-15Created from EPrint's last_modified field